Cellulose ether, is widely used in mortar. As a kind of etherified cellulose, cellulose ether has affinity for water, and this polymer compound has excellent water absorption and water retention ability, which can well solve the bleeding of mortar, short operation time, stickiness, etc. Insufficient knot strength and many other problems.
With the continuous development of world’s construction industry and the continuous deepening of building materials research, the commercialization of mortar has become an irresistible trend. Due to the many advantages that traditional mortar does not have, the use of commercial mortar has become more common in large and medium-sized cities in my country. However, commercial mortar still has many technical problems.
High fluidity mortar, such as reinforcement mortar, cement-based grouting materials, etc., due to the large amount of water reducing agent used, will cause serious bleeding phenomenon and affect the comprehensive performance of mortar; It is very sensitive, and it is prone to serious decrease in workability due to water loss in a short period of time after mixing, which means that the operation time is extremely short; in addition, for bonded mortar, if the mortar has insufficient water retention ability, a large amount of Moisture will be absorbed by the matrix, resulting in partial water shortage of the bonding mortar, and therefore insufficient hydration, resulting in a decrease in strength and a decrease in cohesive force.
In addition, admixtures as partial substitutes for cement, such as fly ash, granulated blast furnace slag powder (mineral powder), silica fume, etc., are now more and more important. As industrial by-products and wastes, if the admixture cannot be fully utilized, its accumulation will occupy and destroy a large amount of land, and will cause serious environmental pollution. If admixtures are used reasonably, they can improve certain properties of concrete and mortar, and solve the engineering problems of concrete and mortar in certain applications. Therefore, the wide application of admixtures is beneficial to the environment and industry benefits.
Many studies have been done at home and abroad on the effect of cellulose ether and admixtures on mortar, but there is still a lack of discussion on the effect of the combined use of the two.
In this paper, the important admixtures in mortar, cellulose ether and admixture are used in the mortar, and the comprehensive influence law of the two components in the mortar on the fluidity and strength of the mortar is summarized through experiments. By changing the type and amount of cellulose ether and admixtures in the test, the influence on the fluidity and strength of the mortar was observed (in this paper, the test gelling system mainly adopts a binary system). Compared with HPMC, CMC is not suitable for thickening and water retention treatment of cement-based cementitious materials. HPMC can significantly reduce the fluidity of slurry and increase the loss over time at low dosage (below 0.2%). Reduce the strength of the mortar body and reduce the compression-to-fold ratio. Comprehensive fluidity and strength requirements, HPMC content in O. 1% is more appropriate. In terms of admixtures, fly ash has a certain effect on increasing the fluidity of the slurry, and the influence of slag powder is not obvious. Although silica fume can effectively reduce bleeding, the fluidity can be seriously lost when the dosage is 3%. . After comprehensive consideration, it is concluded that when fly ash is used in structural or reinforced mortar with requirements of fast hardening and early strength, the dosage should not be too high, the maximum dosage is about 10%, and when it is used for bonding mortar, it is added to 20%. ‰ can also basically meet the requirements; considering factors such as the poor volume stability of mineral powder and silica fume, it should be controlled below 10% and 3% respectively. The effects of admixtures and cellulose ethers were not significantly correlated and had independent effects.
In addition, referring to Feret’s strength theory and the activity coefficient of admixtures, this paper proposes a new prediction method for the compressive strength of cement-based materials. By discussing the activity coefficient of mineral admixtures and Feret’s strength theory from the volume point of view and ignoring the interaction between different admixtures, this method concludes that admixtures, water consumption and aggregate composition have many influences on concrete. The influence law of (mortar) strength has good guiding significance.
Through the above work, this paper draws some theoretical and practical conclusions with certain reference value.
Keywords: cellulose ether, mortar fluidity, workability, mineral admixture, strength prediction
Chapter 1 Introduction
1.1 commodity mortar
1.1.1 Introduction of commercial mortar
In my country’s building materials industry, concrete has achieved a high degree of commercialization, and the commercialization of mortar is also getting higher and higher, especially for various special mortars, manufacturers with higher technical capabilities are required to ensure the various mortars. The performance indicators are qualified. Commercial mortar is divided into two categories: ready-mixed mortar and dry-mixed mortar. Ready-mixed mortar means that the mortar is transported to the construction site after being mixed with water by the supplier in advance according to the project requirements, while dry-mixed mortar is made by the mortar manufacturer by dry-mixing and packaging cementitious materials, aggregates and additives according to a certain ratio. Add a certain amount of water to the construction site and mix it before use.
Traditional mortar has many weaknesses in use and performance. For example, the stacking of raw materials and on-site mixing cannot meet the requirements of civilized construction and environmental protection. In addition, due to on-site construction conditions and other reasons, it is easy to make the quality of mortar difficult to guarantee, and it is impossible to obtain high performance. mortar. Compared with traditional mortar, commercial mortar has some obvious advantages. First of all, its quality is easy to control and guarantee, its performance is superior, its types are refined, and it is better targeted to engineering requirements. European dry-mixed mortar has been developed in the 1950s, and my country is also vigorously advocating the application of commercial mortar. Shanghai has already used commercial mortar in 2004. With the continuous development of my country’s urbanization process, at least in the urban market, it will be inevitable that commercial mortar with various advantages will replace traditional mortar.
1.1.2 Problems existing in commercial mortar
Although commercial mortar has many advantages over traditional mortar, there are still many technical difficulties as mortar. High fluidity mortar, such as reinforcement mortar, cement-based grouting materials, etc., have extremely high requirements on strength and work performance, so the use of superplasticizers is large, which will cause serious bleeding and affect the mortar. Comprehensive performance; and for some plastic mortars, because they are very sensitive to the loss of water, it is easy to have a serious decrease in workability due to the loss of water in a short time after mixing, and the operation time is extremely short: In addition, for In terms of bonding mortar, the bonding matrix is often relatively dry. During the construction process, due to the insufficient ability of the mortar to retain water, a large amount of water will be absorbed by the matrix, resulting in local water shortage of the bonding mortar and insufficient hydration. The phenomenon that the strength decreases and the adhesive force decreases.
In response to the above questions, an important additive, cellulose ether, is widely used in mortar. As a kind of etherified cellulose, cellulose ether has affinity for water, and this polymer compound has excellent water absorption and water retention ability, which can well solve the bleeding of mortar, short operation time, stickiness, etc. Insufficient knot strength and many other problems.
In addition, admixtures as partial substitutes for cement, such as fly ash, granulated blast furnace slag powder (mineral powder), silica fume, etc., are now more and more important. We know that most of the admixtures are by-products of industries such as electric power, smelting steel, smelting ferrosilicon and industrial silicon. If they cannot be fully utilized, the accumulation of admixtures will occupy and destroy a large amount of land and cause serious damage. environmental pollution. On the other hand, if admixtures are used reasonably, some properties of concrete and mortar can be improved, and some engineering problems in the application of concrete and mortar can be well solved. Therefore, the wide application of admixtures is beneficial to the environment and industry. are beneficial.
1.2 Cellulose ethers
Cellulose ether (cellulose ether) is a polymer compound with ether structure produced by etherification of cellulose. Each glucosyl ring in cellulose macromolecules contains three hydroxyl groups, a primary hydroxyl group on the sixth carbon atom, a secondary hydroxyl group on the second and third carbon atoms, and the hydrogen in the hydroxyl group is replaced by a hydrocarbon group to generate cellulose ether derivatives. thing. Cellulose is a polyhydroxy polymer compound that neither dissolves nor melts, but cellulose can be dissolved in water, dilute alkali solution and organic solvent after etherification, and has a certain thermoplasticity.
Cellulose ether takes natural cellulose as raw material and is prepared by chemical modification. It is classified into two categories: ionic and non-ionic in ionized form. It is widely used in chemical, petroleum, construction, medicine, ceramics and other industries. .
1.2.1 Classification of cellulose ethers for construction
Cellulose ether for construction is a general term for a series of products produced by the reaction of alkali cellulose and etherifying agent under certain conditions. Different kinds of cellulose ethers can be obtained by replacing alkali cellulose with different etherifying agents.
1. According to the ionization properties of the substituents, cellulose ethers can be divided into two categories: ionic (such as carboxymethyl cellulose) and non-ionic (such as methyl cellulose).
2. According to the types of substituents, cellulose ethers can be divided into single ethers (such as methyl cellulose) and mixed ethers (such as hydroxypropyl methyl cellulose).
3. According to different solubility, it is divided into water-soluble (such as hydroxyethyl cellulose) and organic solvent solubility (such as ethyl cellulose), etc. The main application type in dry-mixed mortar is water-soluble cellulose, while water-soluble cellulose It is divided into instant type and delayed dissolution type after surface treatment.
1.2.2 Explanation of the mechanism of action of cellulose ether in mortar
Cellulose ether is a key admixture to improve the water retention properties of dry-mixed mortar, and it is also one of the key admixtures to determine the cost of dry-mixed mortar materials.
1. After the cellulose ether in the mortar is dissolved in water, the unique surface activity ensures that the cementitious material is effectively and uniformly dispersed in the slurry system, and cellulose ether, as a protective colloid, can “encapsulate” solid particles, Thus, a lubricating film is formed on the outer surface, and the lubricating film can make the mortar body have good thixotropy. That is to say, the volume is relatively stable in the standing state, and there will be no adverse phenomena such as bleeding or stratification of light and heavy substances, which makes the mortar system more stable; while in the agitated construction state, the cellulose ether will play a role in reducing the shearing of the slurry. The effect of variable resistance makes the mortar have good fluidity and smoothness during construction during the mixing process.
2. Due to the characteristics of its own molecular structure, the cellulose ether solution can keep water and not easily lost after being mixed into the mortar, and will be gradually released in a long period of time, which prolongs the operation time of the mortar and gives the mortar good water retention and operability.
1.2.3 Several important construction grade cellulose ethers
1. Methyl Cellulose (MC)
After the refined cotton is treated with alkali, methyl chloride is used as the etherifying agent to make cellulose ether through a series of reactions. The general substitution degree is 1. Melting 2.0, the degree of substitution is different and the solubility is also different. Belongs to non-ionic cellulose ether.
2. Hydroxyethyl Cellulose (HEC)
It is prepared by reacting with ethylene oxide as an etherifying agent in the presence of acetone after the refined cotton is treated with alkali. The degree of substitution is generally 1.5 to 2.0. It has strong hydrophilicity and is easy to absorb moisture.
3. Hydroxypropyl methylcellulose (HPMC)
Hydroxypropyl methylcellulose is a cellulose variety whose output and consumption are rapidly increasing in recent years. It is a non-ionic cellulose mixed ether made from refined cotton after alkali treatment, using propylene oxide and methyl chloride as etherifying agents, and through a series of reactions. The degree of substitution is generally 1.2 to 2.0. Its properties vary according to the ratio of methoxyl content and hydroxypropyl content.
4. Carboxymethylcellulose (CMC)
Ionic cellulose ether is prepared from natural fibers (cotton, etc.) after alkali treatment, using sodium monochloroacetate as an etherifying agent, and through a series of reaction treatments. The degree of substitution is generally 0.4–d. 4. Its performance is greatly affected by the degree of substitution.
Among them, the third and fourth types are the two types of cellulose used in this experiment.
1.2.4 Development Status of Cellulose Ether Industry
After years of development, the cellulose ether market in developed countries has become very mature, and the market in developing countries is still in the growth stage, which will become the main driving force for the growth of global cellulose ether consumption in the future. At present, the total global production capacity of cellulose ether exceeds 1 million tons, with Europe accounting for 35% of the total global consumption, followed by Asia and North America. Carboxymethyl cellulose ether (CMC) is the main consumer species, accounting for 56% of the total, followed by methyl cellulose ether (MC/HPMC) and hydroxyethyl cellulose ether (HEC), accounting for 56% of the total. 25% and 12%. The foreign cellulose ether industry is highly competitive. After many integrations, the output is mainly concentrated in several large companies, such as Dow Chemical Company and Hercules Company in the United States, Akzo Nobel in the Netherlands, Noviant in Finland and DAICEL in Japan, etc. .
my country is the world’s largest producer and consumer of cellulose ether, with an average annual growth rate of more than 20%. According to preliminary statistics, there are about 50 cellulose ether production enterprises in China. The designed production capacity of the cellulose ether industry has exceeded 400,000 tons, and there are about 20 enterprises with a capacity of more than 10,000 tons, mainly located in Shandong, Hebei, Chongqing and Jiangsu. , Zhejiang, Shanghai and other places. In 2011, China’s CMC production capacity was about 300,000 tons. With the increasing demand for high-quality cellulose ethers in the pharmaceutical, food, daily chemical and other industries in recent years, the domestic demand for other cellulose ether products other than CMC is increasing. Larger, the capacity of MC/HPMC is about 120,000 tons, and the capacity of HEC is about 20,000 tons. PAC is still in the stage of promotion and application in China. With the development of large offshore oil fields and the development of building materials, food, chemical and other industries, the amount and field of PAC are increasing and expanding year by year, with a production capacity of more than 10,000 tons.
1.3 Research on the application of cellulose ether to mortar
Regarding the engineering application research of cellulose ether in the construction industry, domestic and foreign scholars have conducted a large number of experimental research and mechanism analysis.
1.3.1 Brief introduction of foreign research on the application of cellulose ether to mortar
Laetitia Patural, Philippe Marchal and others in France pointed out that cellulose ether has a significant effect on the water retention of mortar, and the structural parameter is the key, and the molecular weight is the key to control the water retention and consistency. With the increase of molecular weight, the yield stress decreases, the consistency increases, and the water retention performance increases; on the contrary, the molar substitution degree (related to the content of hydroxyethyl or hydroxypropyl) has little effect on the water retention of dry-mixed mortar. However, cellulose ethers with low molar degrees of substitution have improved water retention.
An important conclusion about the water retention mechanism is that the rheological properties of the mortar are critical. It can be seen from the test results that for dry-mixed mortar with a fixed water-cement ratio and admixture content, the water retention performance generally has the same regularity as its consistency. However, for some cellulose ethers, the trend is not obvious; in addition, for starch ethers, there is an opposite pattern. The viscosity of the fresh mix is not the only parameter for determining water retention.
Laetitia Patural, Patrice Potion, et al., with the help of pulsed field gradient and MRI techniques, found that the moisture migration at the interface of mortar and unsaturated substrate is affected by the addition of a small amount of CE. The loss of water is due to capillary action rather than water diffusion. Moisture migration by capillary action is governed by substrate micropore pressure, which in turn is determined by micropore size and Laplace theory interfacial tension, as well as fluid viscosity. This indicates that the rheological properties of CE aqueous solution are the key to water retention performance. However, this hypothesis contradicts some consensus (other tackifiers like high molecular polyethylene oxide and starch ethers are not as effective as CE).
Jean. Yves Petit, Erie Wirquin et al. used cellulose ether through experiments, and its 2% solution viscosity was from 5000 to 44500mpa. S ranging from MC and HEMC. Find:
1. For a fixed amount of CE, the type of CE has a great influence on the viscosity of the adhesive mortar for tiles. This is due to the competition between CE and dispersible polymer powder for the adsorption of cement particles.
2. The competitive adsorption of CE and rubber powder has a significant effect on the setting time and spalling when the construction time is 20-30min.
3. The bond strength is affected by the pairing of CE and rubber powder. When the CE film cannot prevent the evaporation of moisture at the interface of the tile and the mortar, the adhesion under high temperature curing decreases.
4. The coordination and interaction of CE and dispersible polymer powder should be taken into consideration when designing the proportion of adhesive mortar for tiles.
Germany’s LSchmitzC. J. Dr. H(a)cker mentioned in the article that HPMC and HEMC in cellulose ether have a very critical role in water retention in dry-mixed mortar. In addition to ensuring the enhanced water retention index of cellulose ether, it is recommended to use modified Cellulose ethers are used to improve and improve the working properties of mortar and the properties of dry and hardened mortar.
1.3.2 Brief introduction of domestic research on the application of cellulose ether to mortar
Xin Quanchang from Xi’an University of Architecture and Technology studied the influence of various polymers on some properties of bonding mortar, and found that the composite use of dispersible polymer powder and hydroxyethyl methyl cellulose ether can not only improve the performance of bonding mortar, but also can Part of the cost is reduced; the test results show that when the content of redispersible latex powder is controlled at 0.5%, and the content of hydroxyethyl methyl cellulose ether is controlled at 0.2%, the prepared mortar is resistant to bending. and bonding strength are more prominent, and have good flexibility and plasticity.
Professor Ma Baoguo from Wuhan University of Technology pointed out that cellulose ether has obvious retardation effect, and can affect the structural form of hydration products and the pore structure of cement slurry; cellulose ether is mainly adsorbed on the surface of cement particles to form a certain barrier effect. It hinders the nucleation and growth of hydration products; on the other hand, cellulose ether hinders the migration and diffusion of ions due to its obvious viscosity increasing effect, thereby delaying the hydration of cement to a certain extent; cellulose ether has alkali stability.
Jian Shouwei from Wuhan University of Technology concluded that the role of CE in mortar is mainly reflected in three aspects: excellent water retention capacity, influence on mortar consistency and thixotropy, and adjustment of rheology. CE not only gives mortar good working performance, but also To reduce the early hydration heat release of cement and delay the hydration kinetic process of cement, of course, based on the different use cases of mortar, there are also differences in its performance evaluation methods.
CE modified mortar is applied in the form of thin-layer mortar in daily dry-mix mortar (such as brick binder, putty, thin-layer plastering mortar, etc.). This unique structure is usually accompanied by the rapid water loss of the mortar. At present, the main research focuses on the face tile adhesive, and there is less research on other types of thin-layer CE modified mortar.
Su Lei from Wuhan University of Technology obtained through the experimental analysis of the water retention rate, water loss and setting time of the mortar modified with cellulose ether. The amount of water decreases gradually, and the coagulation time is prolonged; when the amount of water reaches O. After 6%, the change of water retention rate and water loss is no longer obvious, and the setting time is nearly doubled; and the experimental study of its compressive strength shows that when the content of cellulose ether is lower than 0.8%, the content of cellulose ether is less than 0.8%. The increase will significantly reduce the compressive strength; and in terms of the bonding performance with the cement mortar board, O. Below 7% of the content, the increase of the content of cellulose ether can effectively improve the bonding strength.
Lai Jianqing of Xiamen Hongye Engineering Construction Technology Co., Ltd. analyzed and concluded that the optimal dosage of cellulose ether when considering the water retention rate and consistency index is 0 through a series of tests on the water retention rate, strength and bond strength of EPS thermal insulation mortar. 2%; cellulose ether has a strong air-entraining effect, which will cause a decrease in strength, especially a decrease in tensile bond strength, so it is recommended to use it together with redispersible polymer powder.
Yuan Wei and Qin Min of Xinjiang Building Materials Research Institute conducted the test and application research of cellulose ether in foamed concrete. The test results show that HPMC improves the water retention performance of fresh foam concrete and reduces the water loss rate of hardened foam concrete; HPMC can reduce the slump loss of fresh foam concrete and reduce the sensitivity of the mixture to temperature. ; HPMC will significantly reduce the compressive strength of foam concrete. Under natural curing conditions, a certain amount of HPMC can improve the strength of the specimen to a certain extent.
Li Yuhai of Wacker Polymer Materials Co., Ltd. pointed out that the type and amount of latex powder, the type of cellulose ether and the curing environment have a significant impact on the impact resistance of plastering mortar. The effect of cellulose ethers on impact strength is also negligible compared to polymer content and curing conditions.
Yin Qingli of AkzoNobel Specialty Chemicals (Shanghai) Co., Ltd. used Bermocoll PADl, a specially modified polystyrene board bonding cellulose ether, for the experiment, which is especially suitable for the bonding mortar of EPS external wall insulation system. Bermocoll PADl can improve the bonding strength between mortar and polystyrene board in addition to all the functions of cellulose ether. Even in the case of low dosage, it can not only improve the water retention and workability of the fresh mortar, but also can significantly improve the original bonding strength and water-resistant bonding strength between the mortar and the polystyrene board due to the unique anchoring technology. . However, it cannot improve the impact resistance of mortar and the bonding performance with polystyrene board. To improve these properties, redispersible latex powder should be used.
Wang Peiming from Tongji University analyzed the development history of commercial mortar and pointed out that cellulose ether and latex powder have a non-negligible impact on the performance indicators such as water retention, flexural and compressive strength, and elastic modulus of dry powder commercial mortar.
Zhang Lin and others of Shantou Special Economic Zone Longhu Technology Co., Ltd. have concluded that, in the bonding mortar of the expanded polystyrene board thin plastering external wall external thermal insulation system (ie Eqos system), it is recommended that the optimum amount of rubber powder be 2.5% is the limit; low viscosity, highly modified cellulose ether is of great help to the improvement of the auxiliary tensile bond strength of hardened mortar.
Zhao Liqun of Shanghai Institute of Building Research (Group) Co., Ltd. pointed out in the article that cellulose ether can significantly improve the water retention of mortar, and also significantly reduce the bulk density and compressive strength of mortar, and prolong the setting time of mortar. Under the same dosage conditions, cellulose ether with high viscosity is beneficial to the improvement of water retention rate of mortar, but the compressive strength decreases more greatly and the setting time is longer. Thickening powder and cellulose ether eliminate plastic shrinkage cracking of mortar by improving the water retention of mortar.
Fuzhou University Huang Lipin et al studied the doping of hydroxyethyl methyl cellulose ether and ethylene. Physical properties and cross-sectional morphology of modified cement mortar of vinyl acetate copolymer latex powder. It is found that cellulose ether has excellent water retention, water absorption resistance and outstanding air-entraining effect, while the water-reducing properties of latex powder and the improvement of the mechanical properties of mortar are particularly prominent. Modification effect; and there is a suitable dosage range between polymers.
Through a series of experiments, Chen Qian and others from Hubei Baoye Construction Industrialization Co., Ltd. proved that extending the stirring time and increasing the stirring speed can give full play to the role of cellulose ether in the ready-mixed mortar, improve the workability of the mortar, and improve the stirring time. Too short or too slow speed will make the mortar difficult to construct; choosing the right cellulose ether can also improve the workability of ready-mixed mortar.
Li Sihan from Shenyang Jianzhu University and others found that mineral admixtures can reduce the dry shrinkage deformation of mortar and improve its mechanical properties; the ratio of lime to sand has an effect on the mechanical properties and shrinkage rate of mortar; redispersible polymer powder can improve the mortar. Crack resistance, improve adhesion, flexural strength, cohesion, impact resistance and wear resistance, improve water retention and workability; cellulose ether has air-entraining effect, which can improve the water retention of mortar; wood fiber can improve mortar Improve the ease of use, operability, and anti-slip performance, and speed up construction. By adding various admixtures for modification, and through a reasonable ratio, crack-resistant mortar for external wall thermal insulation system with excellent performance can be prepared.
Yang Lei of Henan University of Technology mixed HEMC into the mortar and found that it has the dual functions of water retention and thickening, which prevents the air-entrained concrete from quickly absorbing the water in the plastering mortar, and ensures that the cement in the mortar is fully hydrated, making the mortar The combination with aerated concrete is denser and the bond strength is higher; it can greatly reduce the delamination of plastering mortar for aerated concrete. When HEMC was added to the mortar, the flexural strength of the mortar decreased slightly, while the compressive strength decreased greatly, and the fold-compression ratio curve showed an upward trend, indicating that the addition of HEMC could improve the toughness of the mortar.
Li Yanling and others from Henan University of Technology found that the mechanical properties of the bonded mortar were improved compared with ordinary mortar, especially the bond strength of the mortar, when the compound admixture was added (the content of cellulose ether was 0.15%). It is 2.33 times that of ordinary mortar.
Ma Baoguo from Wuhan University of Technology and others studied the effects of different dosages of styrene-acrylic emulsion, dispersible polymer powder, and hydroxypropyl methylcellulose ether on the water consumption, bond strength and toughness of thin plastering mortar. , found that when the content of styrene-acrylic emulsion was 4% to 6%, the bond strength of mortar reached the best value, and the compression-folding ratio was the smallest; the content of cellulose ether increased to O. At 4%, the bond strength of mortar reaches saturation, and the compression-folding ratio is the smallest; when the content of rubber powder is 3%, the bonding strength of mortar is the best, and the compression-folding ratio decreases with the addition of rubber powder. trend.
Li Qiao and others of Shantou Special Economic Zone Longhu Technology Co., Ltd. pointed out in the article that the functions of cellulose ether in cement mortar are water retention, thickening, air entrainment, retardation and improvement of tensile bond strength, etc. These functions correspond to When examining and selecting MC, the indicators of MC that need to be considered include viscosity, degree of etherification substitution, degree of modification, product stability, effective substance content, particle size and other aspects. When choosing MC in different mortar products, the performance requirements for MC itself should be put forward according to the construction and use requirements of specific mortar products, and the appropriate MC varieties should be selected in combination with the composition and basic index parameters of MC.
Qiu Yongxia of Beijing Wanbo Huijia Science and Trade Co., Ltd. found that with the increase of the viscosity of cellulose ether, the water retention rate of the mortar increased; the finer the particles of cellulose ether, the better the water retention; The higher the water retention rate of cellulose ether; the water retention of cellulose ether decreases with the increase of mortar temperature.
Zhang Bin of Tongji University and others pointed out in the article that the working characteristics of modified mortar are closely related to the viscosity development of cellulose ethers, not that the cellulose ethers with high nominal viscosity have obvious influence on the working characteristics, because they are also affected by the particle size. , dissolution rate and other factors.
Zhou Xiao and others from the Institute of Cultural Relics Protection Science and Technology, China Cultural Heritage Research Institute studied the contribution of two additives, polymer rubber powder and cellulose ether, to the bond strength in NHL (hydraulic lime) mortar system, and found that the simple Due to the excessive shrinkage of hydraulic lime, it cannot produce sufficient tensile strength with the stone interface. An appropriate amount of polymer rubber powder and cellulose ether can effectively improve the bonding strength of NHL mortar and meet the requirements of cultural relic reinforcement and protection materials; in order to prevent It has an impact on the water permeability and breathability of NHL mortar itself and the compatibility with masonry cultural relics. At the same time, considering the initial bonding performance of NHL mortar, the ideal addition amount of polymer rubber powder is below 0.5% to 1%, and the addition of cellulose ether The amount is controlled at about 0.2%.
Duan Pengxuan and others from the Beijing Institute of Building Materials Science made two self-made rheological testers on the basis of establishing the rheological model of fresh mortar, and conducted rheological analysis of ordinary masonry mortar, plastering mortar and plastering gypsum products. The denaturation was measured, and it was found that hydroxyethyl cellulose ether and hydroxypropyl methyl cellulose ether have better initial viscosity value and viscosity reduction performance with time and speed increase, which can enrich the binder for better bonding type, thixotropy and slip resistance.
Li Yanling of Henan University of Technology and others found that the addition of cellulose ether in the mortar can greatly improve the water retention performance of the mortar, thereby ensuring the progress of cement hydration. Although the addition of cellulose ether reduces the flexural strength and compressive strength of the mortar, it still increases the flexural-compression ratio and the bond strength of the mortar to a certain extent.
1.4 Research on the application of admixtures to mortar at home and abroad
In today’s construction industry, the production and consumption of concrete and mortar is huge, and the demand for cement is also increasing. The production of cement is a high energy consumption and high pollution industry. Saving cement is of great significance to control costs and protect the environment. As a partial substitute for cement, mineral admixture can not only optimize the performance of mortar and concrete, but also save a lot of cement under the condition of reasonable utilization.
In the building materials industry, the application of admixtures has been very extensive. Many cement varieties contain more or less a certain amount of admixtures. Among them, the most widely used ordinary Portland cement is added 5% in the production. ~20% admixture. In the production process of various mortar and concrete production enterprises, the application of admixtures is more extensive.
For the application of admixtures in mortar, long-term and extensive research has been carried out at home and abroad.
1.4.1 Brief introduction of foreign research on admixture applied to mortar
P. University of California. J. M. Momeiro Joe IJ K. Wang et al. found that in the hydration process of the gelling material, the gel is not swelled in equal volume, and the mineral admixture can change the composition of the hydrated gel, and found that the swelling of the gel is related to the divalent cations in the gel. The number of copies showed a significant negative correlation.
Kevin J. of the United States. Folliard and Makoto Ohta et al. pointed out that the addition of silica fume and rice husk ash to the mortar can significantly improve the compressive strength, while the addition of fly ash reduces the strength, especially in the early stage.
Philippe Lawrence and Martin Cyr of France found that a variety of mineral admixtures can improve the mortar strength under the appropriate dosage. The difference between different mineral admixtures is not obvious in the early stage of hydration. In the later stage of hydration, the additional strength increase is affected by the activity of the mineral admixture, and the strength increase caused by the inert admixture cannot simply be regarded as filling. effect, but should be attributed to the physical effect of multiphase nucleation.
Bulgaria’s ValIly0 Stoitchkov Stl Petar Abadjiev and others found that the basic components are silica fume and low-calcium fly ash through the physical and mechanical properties of cement mortar and concrete mixed with active pozzolanic admixtures, which can improve the strength of cement stone. Silica fume has a significant effect on the early hydration of cementitious materials, while the fly ash component has an important effect on the later hydration.
1.4.2 Brief introduction of domestic research on the application of admixtures to mortar
Through experimental research, Zhong Shiyun and Xiang Keqin of Tongji University found that the composite modified mortar of a certain fineness of fly ash and polyacrylate emulsion (PAE), when the poly-binder ratio was fixed at 0.08, the compression-folding ratio of the mortar increased with the The fineness and content of fly ash decrease with the increase of fly ash. It is proposed that the addition of fly ash can effectively solve the problem of high cost of improving the flexibility of mortar by simply increasing the content of polymer.
Wang Yinong of Wuhan Iron and Steel Civil Construction Company has studied a high-performance mortar admixture, which can effectively improve the workability of mortar, reduce the degree of delamination, and improve the bonding ability. It is suitable for masonry and plastering of aerated concrete blocks. .
Chen Miaomiao and others from Nanjing University of Technology studied the effect of double mixing fly ash and mineral powder in dry mortar on the working performance and mechanical properties of mortar, and found that the addition of two admixtures not only improved the working performance and mechanical properties of the mixture. The physical and mechanical properties can also effectively reduce the cost. The recommended optimal dosage is to replace 20% of fly ash and mineral powder respectively, the ratio of mortar to sand is 1:3, and the ratio of water to material is 0.16.
Zhuang Zihao from South China University of Technology fixed the water-binder ratio, modified bentonite, cellulose ether and rubber powder, and studied the properties of the mortar strength, water retention and dry shrinkage of three mineral admixtures, and found that the admixture content reached At 50%, the porosity increases significantly and the strength decreases, and the optimal proportion of the three mineral admixtures is 8% limestone powder, 30% slag, and 4% fly ash, which can achieve water retention. rate, the preferred value of intensity.
Li Ying from Qinghai University conducted a series of tests of mortar mixed with mineral admixtures, and concluded and analyzed that mineral admixtures can optimize the secondary particle gradation of powders, and the micro-filling effect and secondary hydration of admixtures can To a certain extent, the compactness of the mortar is increased, thereby increasing its strength.
Zhao Yujing of Shanghai Baosteel New Building Materials Co., Ltd. used the theory of fracture toughness and fracture energy to study the influence of mineral admixtures on the brittleness of concrete. The test shows that the mineral admixture can slightly improve the fracture toughness and fracture energy of mortar; in the case of the same type of admixture, the replacement amount of 40% of the mineral admixture is the most beneficial to the fracture toughness and fracture energy.
Xu Guangsheng of Henan University pointed out that when the specific surface area of the mineral powder is less than E350m2/l [g, the activity is low, the 3d strength is only about 30%, and the 28d strength develops to 0~90%; while at 400m2 melon g, the 3d strength It can be close to 50%, and the 28d strength is above 95%. From the perspective of basic principles of rheology, according to the experimental analysis of mortar fluidity and flow velocity, several conclusions are drawn: fly ash content below 20% can effectively improve mortar fluidity and flow velocity, and mineral powder in When the dosage is below 25%, the fluidity of the mortar can be increased but the flow rate is reduced.
Professor Wang Dongmin of China University of Mining and Technology and Professor Feng Lufeng of Shandong Jianzhu University pointed out in the article that concrete is a three-phase material from the perspective of composite materials, namely cement paste, aggregate, cement paste and aggregate. The interface transition zone ITZ (Interfacial Transition Zone) at the junction. ITZ is a water-rich area, the local water-cement ratio is too large, the porosity after hydration is large, and it will cause the enrichment of calcium hydroxide. This area is most likely to cause initial cracks, and it is most likely to cause stress. Concentration largely determines the intensity. The experimental study shows that the addition of admixtures can effectively improve the endocrine water in the interface transition zone, reduce the thickness of the interface transition zone, and improve the strength.
Zhang Jianxin of Chongqing University and others found that by comprehensive modification of methyl cellulose ether, polypropylene fiber, redispersible polymer powder, and admixtures, a dry-mixed plastering mortar with good performance can be prepared. Dry-mixed crack-resistant plastering mortar has good workability, high bond strength and good crack resistance. The quality of drums and cracks is a common problem.
Ren Chuanyao of Zhejiang University and others studied the effect of hydroxypropyl methylcellulose ether on the properties of fly ash mortar, and analyzed the relationship between wet density and compressive strength. It was found that adding hydroxypropyl methyl cellulose ether into fly ash mortar can significantly improve the water retention performance of mortar, prolong the bonding time of mortar, and reduce the wet density and compressive strength of mortar. There is a good correlation between wet density and 28d compressive strength. Under the condition of known wet density, the 28d compressive strength can be calculated by using the fitting formula.
Professor Pang Lufeng and Chang Qingshan of Shandong Jianzhu University used the uniform design method to study the influence of the three admixtures of fly ash, mineral powder and silica fume on the strength of concrete, and put forward a prediction formula with certain practical value through regression analysis. , and its practicability was verified.
1.5 Purpose and significance of this study
As an important water-retaining thickener, cellulose ether is widely used in food processing, mortar and concrete production and other industries. As an important admixture in various mortars, a variety of cellulose ethers can significantly reduce the bleeding of high fluidity mortar, enhance the thixotropy and construction smoothness of the mortar, and improve the water retention performance and bond strength of the mortar.
The application of mineral admixtures is increasingly widespread, which not only solves the problem of processing a large number of industrial by-products, saves land and protects the environment, but also can turn waste into treasure and create benefits.
There have been many studies on the components of the two mortars at home and abroad, but there are not many experimental studies that combine the two together. The purpose of this paper is to mix several cellulose ethers and mineral admixtures into the cement paste at the same time , high fluidity mortar and plastic mortar (taking the bonding mortar as an example), through the exploration test of fluidity and various mechanical properties, the influence law of the two kinds of mortars when the components are added together is summarized, which will affect the future cellulose ether. And the further application of mineral admixtures provides a certain reference.
In addition, this paper proposes a method for predicting the strength of mortar and concrete based on the FERET strength theory and the activity coefficient of mineral admixtures, which can provide a certain guiding significance for the mix ratio design and strength prediction of mortar and concrete.
1.6 The main research content of this paper
The main research contents of this paper include:
1. By compounding several cellulose ethers and various mineral admixtures, experiments on the fluidity of clean slurry and high-fluidity mortar were carried out, and the influence laws were summarized and the reasons were analyzed.
2. By adding cellulose ethers and various mineral admixtures to high fluidity mortar and bonding mortar, explore their effects on compressive strength, flexural strength, compression-folding ratio and bonding mortar of high fluidity mortar and plastic mortar The law of influence on the tensile bond strength.
3. Combined with the FERET strength theory and the activity coefficient of mineral admixtures, a strength prediction method for multi-component cementitious material mortar and concrete is proposed.
Chapter 2 Analysis of raw materials and their components for testing
2.1 Test materials
2.1.1 Cement (C)
The test used the "Shanshui Dongyue" brand PO. 42.5 Cement.
2.1.2 Mineral powder (KF)
The $95 grade granulated blast furnace slag powder from Shandong Jinan Luxin New Building Materials Co., Ltd. was selected.
2.1.3 Fly Ash (FA)
The grade II fly ash produced by Jinan Huangtai Power Plant is selected, the fineness (remaining sieve of 459m square hole sieve) is 13%, and the water demand ratio is 96%.
2.1.4 Silica fume (sF)
Silica fume adopts the silica fume of Shanghai Aika Silica Fume Material Co., Ltd., its density is 2.59/cm3; the specific surface area is 17500m2/kg, and the average particle size is O. 1～0.39m, 28d activity index is 108%, water demand ratio is 120%.
2.1.5 Redispersible latex powder (JF)
The rubber powder adopts Max redispersible latex powder 6070N (bonding type) from Gomez Chemical China Co., Ltd.
2.1.6 Cellulose ether (CE)
CMC adopts coating grade CMC from Zibo Zou Yongning Chemical Co., Ltd., and HPMC adopts two kinds of hydroxypropyl methylcellulose from Gomez Chemical China Co., Ltd.
2.1.7 Other admixtures
Heavy calcium carbonate, wood fiber, water repellent, calcium formate, etc.
2.1,8 quartz sand
The machine-made quartz sand adopts four kinds of fineness: 10-20 mesh, 20-40 H, 40.70 mesh and 70.140 H, the density is 2650 kg/rn3, and the stack combustion is 1620 kg/m3.
2.1.9 Polycarboxylate superplasticizer powder (PC)
The polycarboxylate powder of Suzhou Xingbang Chemical Building Materials Co., Ltd.) is 1J1030, and the water reduction rate is 30%.
2.1.10 Sand (S)
The medium sand of Dawen River in Tai'an is used.
2.1.11 Coarse aggregate (G)
Use Jinan Ganggou to produce 5" ~ 25 crushed stone.
2.2 Test method
2.2.1 Test method for slurry fluidity
Test equipment: NJ. 160 type cement slurry mixer, produced by Wuxi Jianyi Instrument Machinery Co., Ltd.
The test methods and results are calculated according to the test method for the fluidity of cement paste in Appendix A of "GB 50119.2003 Technical Specifications for the Application of Concrete Admixtures" or ((GB/T8077--2000 Test Method for Homogeneousness of Concrete Admixtures).
2.2.2 Test method for fluidity of high fluidity mortar
Test equipment: JJ. Type 5 cement mortar mixer, produced by Wuxi Jianyi Instrument Machinery Co., Ltd.;
TYE-2000B mortar compression testing machine, produced by Wuxi Jianyi Instrument Machinery Co., Ltd.;
TYE-300B mortar bending test machine, produced by Wuxi Jianyi Instrument Machinery Co., Ltd.
Mortar fluidity detection method is based on "JC. T 986-2005 Cement-based grouting materials" and "GB 50119-2003 Technical Specifications for the Application of Concrete Admixtures" Appendix A, the size of the cone die used, the height is 60mm, the inner diameter of the upper port is 70mm, the inner diameter of the lower port is 100mm, and the outer diameter of the lower port is 120mm, and the total dry weight of the mortar should not be less than 2000g each time.
The test results of the two fluidities should take the average value of the two vertical directions as the final result.
2.2.3 Test method for tensile bond strength of bonded mortar
Main test equipment: WDL. Type 5 electronic universal testing machine, produced by Tianjin Gangyuan Instrument Factory.
The test method for tensile bond strength shall be implemented with reference to Section 10 of (JGJ/T70.2009 Standard for Test Methods for Basic Properties of Building Mortars.
Chapter 3. Effect of cellulose ether on pure paste and mortar of binary cementitious material of various mineral admixtures
Liquidity Impact
This chapter explores several cellulose ethers and mineral blends by testing a large number of multi-level pure cement-based slurries and mortars and binary cementitious system slurries and mortars with various mineral admixtures and their fluidity and loss over time. The influence law of compound use of materials on the fluidity of clean slurry and mortar, and the influence of various factors are summarized and analyzed.
3.1 Outline of the experimental protocol
In view of the influence of cellulose ether on the working performance of pure cement system and various cementitious material systems, we mainly study in two forms:
1. puree. It has the advantages of intuition, simple operation and high accuracy, and is most suitable for the detection of the adaptability of the admixtures such as cellulose ether to the gelling material, and the contrast is obvious.
2. High fluidity mortar. Achieving a high flow state is also for the convenience of measurement and observation. Here, the adjustment of the reference flow state is mainly controlled by high-performance superplasticizers. In order to reduce the test error, we use a polycarboxylate water reducer with wide adaptability to cement, which is sensitive to temperature, and the test temperature needs to be strictly controlled.
3.2 Influence test of cellulose ether on the fluidity of pure cement paste
3.2.1 Test scheme for the effect of cellulose ether on the fluidity of pure cement paste
Aiming at the influence of cellulose ether on the fluidity of the pure slurry, the pure cement slurry of the one-component cementitious material system was first used to observe the influence. The main reference index here adopts the most intuitive fluidity detection.
The following factors are considered to affect mobility:
1. Types of cellulose ethers
2. Cellulose ether content
3. Slurry rest time
Here, we fixed the PC content of the powder at 0.2%. Three groups and four groups of tests were used for three kinds of cellulose ethers (carboxymethylcellulose sodium CMC, hydroxypropyl methylcellulose HPMC). For sodium carboxymethyl cellulose CMC, the dosage of 0%, O. 10%, O. 2%, namely Og, 0.39, 0.69 (the amount of cement in each test is 3009). , for hydroxypropyl methyl cellulose ether, the dosage is 0%, O. 05%, O. 10%, O. 15%, namely 09, 0.159, 0.39, 0.459.
3.2.2 Test results and analysis of the effect of cellulose ether on the fluidity of pure cement paste
(1) The fluidity test results of pure cement paste mixed with CMC
Analysis of test results:
1. Mobility indicator:
Comparing the three groups with the same standing time, in terms of initial fluidity, with the addition of CMC, the initial fluidity decreased slightly; the half-hour fluidity decreased greatly with the dosage, mainly due to the half-hour fluidity of the blank group. It is 20mm larger than the initial (this may be caused by the retardation of PC powder): -IJ, the fluidity decreases slightly at 0.1% dosage, and increases again at 0.2% dosage .
Comparing the three groups with the same dosage, the fluidity of the blank group was the largest in half an hour, and decreased in one hour (this may be due to the fact that after one hour, the cement particles appeared more hydration and adhesion, the inter-particle structure was initially formed, and the slurry appeared more. Condensation); the fluidity of C1 and C2 groups decreased slightly in half an hour, indicating that the water absorption of CMC had a certain impact on the state; while at the content of C2, there was a large increase in one hour, indicating that the content of The effect of the retardation effect of CMC is dominant.
2. Phenomenon description analysis:
It can be seen that with the increase of the content of CMC, the phenomenon of scratching begins to appear, indicating that CMC has a certain effect on increasing the viscosity of the cement paste, and the air-entraining effect of CMC causes the generation of air bubbles.
(2) The fluidity test results of pure cement paste mixed with HPMC (viscosity 100,000)
Analysis of test results:
1. Mobility indicator:
From the line graph of the effect of standing time on fluidity, it can be seen that the fluidity in half an hour is relatively large compared with the initial and one hour, and with the increase of the content of HPMC, the trend is weakened. Overall, the loss of fluidity is not large, indicating that HPMC has obvious water retention to the slurry, and has a certain retarding effect.
It can be seen from the observation that the fluidity is extremely sensitive to the content of HPMC. In the experimental range, the larger the content of HPMC, the smaller the fluidity. It is basically difficult to fill the fluidity cone mold by itself under the same amount of water. It can be seen that after adding HPMC, the fluidity loss caused by time is not large for the pure slurry.
2. Phenomenon description analysis:
The blank group has bleeding phenomenon, and it can be seen from the sharp change of fluidity with the dosage that HPMC has much stronger water retention and thickening effect than CMC, and plays an important role in eliminating bleeding phenomenon. The large air bubbles should not be understood as the effect of air entrainment. In fact, after the viscosity increases, the air mixed in during the stirring process cannot be beaten into small air bubbles because the slurry is too viscous.
(3) The fluidity test results of pure cement paste mixed with HPMC (viscosity of 150,000)
Analysis of test results:
1. Mobility indicator:
From the line graph of the influence of the content of HPMC (150,000) on the fluidity, the influence of the change of the content on the fluidity is more obvious than that of 100,000 HPMC, indicating that the increase of the viscosity of HPMC will reduce the fluidity.
As far as observation is concerned, according to the overall trend of the change of fluidity with time, the half-hour retarding effect of HPMC (150,000) is obvious, while the effect of -4, is worse than that of HPMC (100,000).
2. Phenomenon description analysis:
There was bleeding in the blank group. The reason for scratching the plate was because the water-cement ratio of the bottom slurry became smaller after bleeding, and the slurry was dense and difficult to scrape from the glass plate. The addition of HPMC played an important role in eliminating the bleeding phenomenon. With the increase of the content, a small amount of small bubbles first appeared and then large bubbles appeared. Small bubbles are mainly caused by a certain cause. Similarly, large bubbles should not be understood as the effect of air entrainment. In fact, after the viscosity increases, the air mixed in during the stirring process is too viscous and cannot overflow from the slurry.
3.3 Influence test of cellulose ether on the fluidity of pure slurry of multi-component cementitious materials
This section mainly explores the effect of the compound use of several admixtures and three cellulose ethers (carboxymethyl cellulose sodium CMC, hydroxypropyl methyl cellulose HPMC) on the fluidity of the pulp.
Similarly, three groups and four groups of tests were used for three kinds of cellulose ethers (carboxymethylcellulose sodium CMC, hydroxypropyl methylcellulose HPMC). For sodium carboxymethyl cellulose CMC, the dosage of 0%, 0.10%, and 0.2%, namely 0g, 0.3g, and 0.6g (the cement dosage for each test is 300g). For hydroxypropyl methylcellulose ether, the dosage is 0%, 0.05%, 0.10%, 0.15%, namely 0g, 0.15g, 0.3g, 0.45g. The PC content of the powder is controlled at 0.2%.
The fly ash and slag powder in the mineral admixture are replaced by the same amount of internal mixing method, and the mixing levels are 10%, 20% and 30%, that is, the replacement amount is 30g, 60g and 90g. However, considering the influence of higher activity, shrinkage, and state, the silica fume content is controlled to 3%, 6%, and 9%, that is, 9g, 18g, and 27g.
3.3.1 Test scheme for the effect of cellulose ether on the fluidity of the pure slurry of the binary cementitious material
(1) Test scheme for the fluidity of binary cementitious materials mixed with CMC and various mineral admixtures.
(2) Test plan for the fluidity of binary cementitious materials mixed with HPMC (viscosity 100,000) and various mineral admixtures.
(3) Test scheme for the fluidity of binary cementitious materials mixed with HPMC (viscosity of 150,000) and various mineral admixtures.
3.3.2 Test results and analysis of the effect of cellulose ether on the fluidity of multi-component cementitious materials
(1) The initial fluidity test results of the binary cementitious material pure slurry mixed with CMC and various mineral admixtures.
It can be seen from this that the addition of fly ash can effectively increase the initial fluidity of the slurry, and it tends to expand with the increase of fly ash content. At the same time, when the content of CMC increases, the fluidity decreases slightly, and the maximum decrease is 20mm.
It can be seen that the initial fluidity of the pure slurry can be increased at low dosage of mineral powder, and the improvement of fluidity is no longer obvious when the dosage is above 20%. At the same time, the amount of CMC in O. At 1%, the fluidity is maximum.
It can be seen from this that the content of silica fume generally has a significant negative effect on the initial fluidity of the slurry. At the same time, CMC also slightly reduced the fluidity.
Half-hour fluidity test results of pure binary cementitious material mixed with CMC and various mineral admixtures.
It can be seen that the improvement of the fluidity of fly ash for half an hour is relatively effective at low dosage, but it may also be because it is close to the flow limit of the pure slurry. At the same time, CMC still has a small reduction in fluidity.
In addition, comparing the initial and half-hour fluidity, it can be found that more fly ash is beneficial to control the loss of fluidity over time.
It can be seen from this that the total amount of mineral powder has no obvious negative effect on the fluidity of the pure slurry for half an hour, and the regularity is not strong. At the same time, the effect of CMC content on the fluidity in half an hour is not obvious, but the improvement of 20% mineral powder replacement group is relatively obvious.
It can be seen that the negative effect of the fluidity of the pure slurry with the amount of silica fume for half an hour is more obvious than the initial one, especially the effect in the range of 6% to 9% is more obvious. At the same time, the decrease of CMC content on the fluidity is about 30mm, which is greater than the decrease of CMC content to the initial.
(2) The initial fluidity test results of the binary cementitious material pure slurry mixed with HPMC (viscosity 100,000) and various mineral admixtures
From this, it can be seen that the effect of fly ash on fluidity is relatively obvious, but it is found in the test that fly ash has no obvious improvement effect on bleeding. In addition, the reducing effect of HPMC on the fluidity is very obvious (especially in the range of 0.1% to 0.15% of high dosage, the maximum decrease can reach more than 50mm).
It can be seen that the mineral powder has little effect on the fluidity, and does not significantly improve the bleeding. In addition, the reducing effect of HPMC on fluidity reaches 60mm in the range of 0.1%～0.15% of high dosage.
From this, it can be seen that the reduction of the fluidity of silica fume is more obvious in the large dosage range, and in addition, the silica fume has obvious improvement effect on bleeding in the test. At the same time, HPMC has an obvious effect on the reduction of fluidity (especially in the range of high dosage (0.1% to 0.15%). In terms of the influencing factors of fluidity, silica fume and HPMC play a key role, and other The admixture acts as an auxiliary small adjustment.
It can be seen that, in general, the effect of the three admixtures on the fluidity is similar to the initial value. When the silica fume is at a high content of 9% and the HPMC content is O. In the case of 15%, the phenomenon that the data could not be collected due to the poor state of the slurry was difficult to fill the cone mold, indicating that the viscosity of silica fume and HPMC increased significantly at higher dosages. Compared with CMC, the viscosity increasing effect of HPMC is very obvious.
(3) The initial fluidity test results of the binary cementitious material pure slurry mixed with HPMC (viscosity 100,000) and various mineral admixtures
From this, it can be seen that HPMC (150,000) and HPMC (100,000) have similar effects on the slurry, but HPMC with high viscosity has a slightly larger decrease in fluidity, but it is not obvious, which should be related to the dissolution of HPMC. The speed has a certain relationship. Among the admixtures, the effect of fly ash content on the fluidity of the slurry is basically linear and positive, and 30% of the content can increase the fluidity by 20,-,30mm; The effect is not obvious, and its improvement effect on bleeding is limited; even at a small dosage level of less than 10%, silica fume has a very obvious effect on reducing bleeding, and its specific surface area is nearly two times larger than that of cement. order of magnitude, the effect of its adsorption of water on the mobility is extremely significant.
In a word, in the respective variation range of the dosage, the factors affecting the fluidity of the slurry, the dosage of silica fume and HPMC is the primary factor, whether it is the control of bleeding or the control of flow state, it is more obvious, other The effect of admixtures is secondary and plays an auxiliary adjustment role.
The third part summarizes the influence of HPMC (150,000) and admixtures on the fluidity of pure pulp in half an hour, which is generally similar to the influence law of the initial value. It can be found that the increase of fly ash on the fluidity of pure slurry for half an hour is slightly more obvious than the increase of initial fluidity, the influence of slag powder is still not obvious, and the influence of silica fume content on fluidity is still very obvious. In addition, in terms of the content of HPMC, there are many phenomena that cannot be poured out at high content, indicating that its O. 15% dosage has a significant effect on increasing viscosity and reducing fluidity, and in terms of fluidity for half an hour, compared with the initial value, the slag group's O. The fluidity of 05% HPMC decreased obviously.
In terms of the loss of fluidity over time, the incorporation of silica fume has a relatively large impact on it, mainly because silica fume has a large fineness, high activity, fast reaction, and strong ability to absorb moisture, resulting in a relatively sensitive fluidity to standing time. To.
3.4 Experiment on the effect of cellulose ether on the fluidity of pure cement-based high-fluidity mortar
3.4.1 Test scheme for the effect of cellulose ether on the fluidity of pure cement-based high-fluidity mortar
Use high fluidity mortar to observe its effect on workability. The main reference index here is the initial and half-hour mortar fluidity test.
The following factors are considered to affect mobility:
1 types of cellulose ethers,
2 Dosage of cellulose ether,
3 Mortar standing time
3.4.2 Test results and analysis of the effect of cellulose ether on the fluidity of pure cement-based high-fluidity mortar
(1) Fluidity test results of pure cement mortar mixed with CMC
Summary and analysis of test results:
1. Mobility indicator:
Comparing the three groups with the same standing time, in terms of initial fluidity, with the addition of CMC, the initial fluidity decreased slightly, and when the content reached O. At 15%, there is a relatively obvious decrease; the decreasing range of the fluidity with the increase of the content in half an hour is similar to the initial value.
2. Symptom:
Theoretically speaking, compared with clean slurry, the incorporation of aggregates in mortar makes it easier for air bubbles to be entrained into the slurry, and the blocking effect of aggregates on bleeding voids will also make it easier for air bubbles or bleeding to be retained. In the slurry, therefore, the air bubble content and size of the mortar should be more and larger than that of the neat slurry. On the other hand, it can be seen that with the increase of the content of CMC, the fluidity decreases, indicating that CMC has a certain thickening effect on the mortar, and the half-hour fluidity test shows that the bubbles overflowing on the surface slightly increase. , which is also a manifestation of the rising consistency, and when the consistency reaches a certain level, the bubbles will be difficult to overflow, and no obvious bubbles will be seen on the surface.
(2) The fluidity test results of pure cement mortar mixed with HPMC (100,000)
Analysis of test results:
1. Mobility indicator:
It can be seen from the figure that with the increase of the content of HPMC, the fluidity is greatly reduced. Compared with CMC, HPMC has a stronger thickening effect. The effect and water retention are better. From 0.05% to 0.1%, the range of fluidity changes is more obvious, and from O. After 1%, neither the initial nor half-hour change in fluidity is too large.
2. Phenomenon description analysis:
It can be seen from the table and figure that there are basically no bubbles in the two groups of Mh2 and Mh3, indicating that the viscosity of the two groups is already relatively large, preventing the overflow of bubbles in the slurry.
(3) The fluidity test results of pure cement mortar mixed with HPMC (150,000)
Analysis of test results:
1. Mobility indicator:
Comparing several groups with the same standing time, the general trend is that both the initial and half-hour fluidity decrease with the increase of the content of HPMC, and the decrease is more obvious than that of HPMC with a viscosity of 100,000, indicating that the increase of the viscosity of HPMC makes it increase. The thickening effect is strengthened, but in O. The effect of the dosage below 05% is not obvious, the fluidity has a relatively large change in the range of 0.05% to 0.1%, and the trend is again in the range of 0.1% to 0.15%. Slow down, or even stop changing. Comparing the half-hour fluidity loss values (initial fluidity and half-hour fluidity) of HPMC with two viscosities, it can be found that HPMC with high viscosity can reduce the loss value, indicating that its water retention and setting retardation effect is better than that of low viscosity.
2. Phenomenon description analysis:
In terms of controlling bleeding, the two HPMCs have little difference in effect, both of which can effectively retain water and thicken, eliminate the adverse effects of bleeding, and at the same time allow bubbles to overflow effectively.
3.5 Experiment on the effect of cellulose ether on the fluidity of high fluidity mortar of various cementitious material systems
3.5.1 Test scheme for the effect of cellulose ethers on the fluidity of high-fluidity mortars of various cementitious material systems
High fluidity mortar is still used to observe its influence on fluidity. The main reference indicators are the initial and half-hour mortar fluidity detection.
(1) Test scheme of mortar fluidity with binary cementitious materials mixed with CMC and various mineral admixtures
(2) Test scheme of mortar fluidity with HPMC (viscosity 100,000) and binary cementitious materials of various mineral admixtures
(3) Test scheme of mortar fluidity with HPMC (viscosity 150,000) and binary cementitious materials of various mineral admixtures
3.5.2 The effect of cellulose ether on the fluidity of high-fluid mortar in a binary cementitious material system of various mineral admixtures Test results and analysis
(1) Initial fluidity test results of binary cementitious mortar mixed with CMC and various admixtures
From the test results of initial fluidity, it can be concluded that the addition of fly ash can slightly improve the fluidity of mortar; when the content of mineral powder is 10%, the fluidity of mortar can be slightly improved; and silica fume has a greater impact on fluidity , especially in the range of 6%~9% content variation, resulting in a decrease in fluidity of about 90mm.
In the two groups of fly ash and mineral powder, CMC reduces the fluidity of mortar to a certain extent, while in the silica fume group, O. The increase of CMC content above 1% no longer significantly affects the fluidity of mortar.
Half-hour fluidity test results of binary cementitious mortar mixed with CMC and various admixtures
From the test results of the fluidity in half an hour, it can be concluded that the effect of the content of admixture and CMC is similar to the initial one, but the content of CMC in the mineral powder group changes from O. 1% to O. The 2% change is larger, at 30mm.
In terms of the loss of fluidity over time, fly ash has the effect of reducing the loss, while the mineral powder and silica fume will increase the loss value under high dosage. The 9% dosage of silica fume also causes the test mold to not be filled by itself. , the fluidity cannot be accurately measured.
(2) The initial fluidity test results of binary cementitious mortar mixed with HPMC (viscosity 100,000) and various admixtures
Half-hour fluidity test results of binary cementitious mortar mixed with HPMC (viscosity 100,000) and various admixtures
It can still be concluded through experiments that the addition of fly ash can slightly improve the fluidity of mortar; when the content of mineral powder is 10%, the fluidity of mortar can be slightly improved; The dosage is very sensitive, and the HPMC group with high dosage at 9% has dead spots, and the fluidity basically disappears.
The content of cellulose ether and silica fume are also the most obvious factors affecting the fluidity of mortar. The effect of HPMC is obviously greater than that of CMC. Other admixtures can improve the loss of fluidity over time.
(3) The initial fluidity test results of binary cementitious mortar mixed with HPMC (viscosity of 150,000) and various admixtures
Half-hour fluidity test results of binary cementitious mortar mixed with HPMC (viscosity 150,000) and various admixtures
It can still be concluded through experiments that the addition of fly ash can slightly improve the fluidity of mortar; when the content of mineral powder is 10%, the fluidity of mortar can be slightly improved: silica fume is still very effective in solving the bleeding phenomenon, while the Fluidity is a serious side effect, but is less effective than its effect in clean slurries.
A large number of dead spots appeared under the high content of cellulose ether (especially in the table of half-hour fluidity), indicating that HPMC has a significant effect on reducing the fluidity of mortar, and mineral powder and fly ash can improve the loss of fluidity over time.
3.5 Chapter Summary
1. Comprehensively comparing the fluidity test of pure cement paste mixed with three cellulose ethers, it can be seen that
1. CMC has certain retarding and air-entraining effects, weak water retention, and certain loss over time.
2. The water retention effect of HPMC is obvious, and it has a significant influence on the state, and the fluidity decreases significantly with the increase of the content. It has a certain air-entraining effect, and the thickening is obvious. 15% will cause large bubbles in the slurry, which is bound to be detrimental to the strength. With the increase of HPMC viscosity, the time-dependent loss of slurry fluidity slightly increased, but not obvious.
2. Comprehensively comparing the slurry fluidity test of the binary gelling system of various mineral admixtures mixed with three cellulose ethers, it can be seen that:
1. The influence law of the three cellulose ethers on the fluidity of the slurry of the binary cementitious system of various mineral admixtures has the characteristics similar to the influence law of the fluidity of the pure cement slurry. CMC has little effect on controlling bleeding, and has a weak effect on reducing fluidity; two kinds of HPMC can increase the viscosity of slurry and reduce fluidity significantly, and the one with higher viscosity has a more obvious effect.
2. Among the admixtures, fly ash has a certain degree of improvement on the initial and half-hour fluidity of the pure slurry, and the content of 30% can be increased by about 30mm; the effect of mineral powder on the fluidity of the pure slurry has no obvious regularity; silicon Although the content of ash is low, its unique ultra-fineness, fast reaction, and strong adsorption make it significantly reduce the fluidity of the slurry, especially when 0.15% HPMC is added, there will be cone molds that cannot be filled. The phenomenon.
3. In the control of bleeding, fly ash and mineral powder are not obvious, and silica fume can obviously reduce the amount of bleeding.
4. In terms of the half-hour loss of fluidity, the loss value of fly ash is smaller, and the loss value of the group incorporating silica fume is larger.
5. In the respective variation range of the content, the factors affecting the fluidity of the slurry, the content of HPMC and silica fume are the primary factors, whether it is the control of the bleeding or the control of the flow state, it is relatively obvious. The influence of mineral powder and mineral powder is secondary, and plays an auxiliary adjustment role.
3. Comprehensively comparing the fluidity test of pure cement mortar mixed with three cellulose ethers, it can be seen that
1. After adding the three cellulose ethers, the bleeding phenomenon was effectively eliminated, and the fluidity of the mortar generally decreased. Certain thickening, water retention effect. CMC has certain retarding and air-entraining effects, weak water retention, and certain loss over time.
2. After adding CMC, the loss of mortar fluidity over time increases, which may be because CMC is an ionic cellulose ether, which is easy to form precipitation with Ca2+ in cement.
3. The comparison of the three cellulose ethers shows that CMC has little effect on the fluidity, and the two kinds of HPMC significantly reduce the fluidity of the mortar at the content of 1/1000, and the one with the higher viscosity is slightly more obvious.
4. The three kinds of cellulose ethers have certain air-entraining effect, which will cause the surface bubbles to overflow, but when the content of HPMC reaches more than 0.1%, due to the high viscosity of the slurry, the bubbles remain in the slurry and cannot overflow.
5. The water retention effect of HPMC is obvious, which has a significant impact on the state of the mixture, and the fluidity decreases significantly with the increase of the content, and the thickening is obvious.
4. Comprehensively compare the fluidity test of multiple mineral admixture binary cementitious materials mixed with three cellulose ethers.
As can be seen:
1. The influence law of three cellulose ethers on the fluidity of multi-component cementitious material mortar is similar to the influence law on the fluidity of pure slurry. CMC has little effect on controlling bleeding, and has a weak effect on reducing fluidity; two kinds of HPMC can increase the viscosity of mortar and reduce fluidity significantly, and the one with higher viscosity has a more obvious effect.
2. Among the admixtures, fly ash has a certain degree of improvement on the initial and half-hour fluidity of the clean slurry; the influence of slag powder on the fluidity of the clean slurry has no obvious regularity; although the content of silica fume is low, its The unique ultra-fineness, fast reaction and strong adsorption make it have a great reduction effect on the fluidity of the slurry. However, compared with the test results of pure paste, it is found that the effect of admixtures tends to weaken.
3. In the control of bleeding, fly ash and mineral powder are not obvious, and silica fume can obviously reduce the amount of bleeding.
4. In the respective variation range of the dosage, the factors affecting the fluidity of the mortar, the dosage of HPMC and silica fume are the primary factors, whether it is the control of bleeding or the control of the flow state, it is more obvious, the silica fume 9% When the content of HPMC is 0.15%, it is easy to cause the filling mold to be difficult to fill, and the influence of other admixtures is secondary and plays an auxiliary adjustment role.
5. There will be bubbles on the surface of the mortar with a fluidity of more than 250mm, but the blank group without cellulose ether generally has no bubbles or only a very small amount of bubbles, indicating that cellulose ether has a certain air-entraining effect and makes the slurry viscous. In addition, due to the excessive viscosity of the mortar with poor fluidity, it is difficult for the air bubbles to float up by the self-weight effect of the slurry, but is retained in the mortar, and its influence on the strength cannot be ignored.
Chapter 4 Effects of Cellulose Ethers on Mechanical Properties of Mortar
The previous chapter studied the effect of the combined use of cellulose ether and various mineral admixtures on the fluidity of the clean slurry and high fluidity mortar. This chapter mainly analyzes the combined use of cellulose ether and various admixtures on the high fluidity mortar And the influence of the compressive and flexural strength of the bonding mortar, and the relationship between the tensile bonding strength of the bonding mortar and the cellulose ether and mineral admixtures is also summarized and analyzed.
According to the research on the working performance of cellulose ether to cement-based material of pure paste and mortar in Chapter 3, in the aspect of strength test, the content of cellulose ether is 0.1%.
4.1 Compressive and flexural strength test of high fluidity mortar
The compressive and flexural strengths of mineral admixtures and cellulose ethers in high-fluidity infusion mortar were investigated.
4.1.1 Influence test on compressive and flexural strength of pure cement-based high fluidity mortar
The effect of three kinds of cellulose ethers on the compressive and flexural properties of pure cement-based high-fluid mortar at various ages at a fixed content of 0.1% was conducted here.
Early strength analysis: In terms of flexural strength, CMC has a certain strengthening effect, while HPMC has a certain reducing effect; in terms of compressive strength, the incorporation of cellulose ether has a similar law with the flexural strength; the viscosity of HPMC affects the two strengths. It has little effect: in terms of the pressure-fold ratio, all three cellulose ethers can effectively reduce the pressure-fold ratio and enhance the flexibility of the mortar. Among them, HPMC with a viscosity of 150,000 has the most obvious effect.
(2) Seven-day strength comparison test results
Seven-day strength analysis: In terms of flexural strength and compressive strength, there is a similar law to the three-day strength. Compared with the three-day pressure-folding, there is a slight increase in the pressure-folding strength. However, the comparison of the data of the same age period can see the effect of HPMC on the reduction of the pressure-folding ratio. relatively obvious.
(3) Twenty-eight days strength comparison test results
Twenty-eight-day strength analysis: In terms of flexural strength and compressive strength, there are similar laws to the three-day strength. The flexural strength increases slowly, and the compressive strength still increases to a certain extent. The data comparison of the same age period shows that HPMC has a more obvious effect on improving the compression-folding ratio.
According to the strength test of this section, it is found that the improvement of the brittleness of the mortar is limited by CMC, and sometimes the compression-to-fold ratio is increased, making the mortar more brittle. At the same time, since the water retention effect is more general than that of HPMC, the cellulose ether we consider for the strength test here is HPMC of two viscosities. Although HPMC has a certain effect on reducing the strength (especially for the early strength), it is beneficial to reduce the compression-refraction ratio, which is beneficial to the toughness of the mortar. In addition, combined with the factors affecting the fluidity in Chapter 3, in the study of the compounding of admixtures and CE In the test of the effect, we will use HPMC (100,000) as the matching CE.
4.1.2 Influence test of compressive and flexural strength of mineral admixture high fluidity mortar
According to the test of the fluidity of pure slurry and mortar mixed with admixtures in the previous chapter, it can be seen that the fluidity of silica fume is obviously deteriorated due to the large water demand, although it can theoretically improve the density and strength to a certain extent. , especially the compressive strength, but it is easy to cause the compression-to-fold ratio to be too large, which makes the mortar brittleness feature remarkable, and it is a consensus that silica fume increases the shrinkage of the mortar. At the same time, due to the lack of skeleton shrinkage of coarse aggregate, the shrinkage value of mortar is relatively large relative to concrete. For mortar (especially special mortar such as bonding mortar and plastering mortar), the biggest harm is often shrinkage. For cracks caused by water loss, strength is often not the most critical factor. Therefore, silica fume was discarded as the admixture, and only fly ash and mineral powder were used to explore the effect of its composite effect with cellulose ether on the strength.
4.1.2.1 Compressive and flexural strength test scheme of high fluidity mortar
In this experiment, the proportion of mortar in 4.1.1 was used, and the content of cellulose ether was fixed at 0.1% and compared with the blank group. The dosage level of the admixture test is 0%, 10%, 20% and 30%.
4.1.2.2 Compressive and flexural strength test results and analysis of high fluidity mortar
It can be seen from the compressive strength test value that the 3d compressive strength after adding HPMC is about 5/VIPa lower than that of the blank group. In general, with the increase of the amount of admixture added, the compressive strength shows a decreasing trend. . In terms of admixtures, the strength of the mineral powder group without HPMC is the best, while the strength of the fly ash group is slightly lower than that of the mineral powder group, indicating that the mineral powder is not as active as the cement, and its incorporation will slightly reduce the early strength of the system. The fly ash with poorer activity reduces the strength more obviously. The reason for the analysis should be that the fly ash mainly participates in the secondary hydration of cement, and does not contribute significantly to the early strength of the mortar.
It can be seen from the flexural strength test values that HPMC still has an adverse effect on the flexural strength, but when the content of the admixture is higher, the phenomenon of reducing the flexural strength is no longer obvious. The reason may be the water retention effect of HPMC. The water loss rate on the surface of the mortar test block is slowed down, and the water for hydration is relatively sufficient.
In terms of admixtures, the flexural strength shows a decreasing trend with the increase of the admixture content, and the flexural strength of the mineral powder group is also slightly larger than that of the fly ash group, indicating that the activity of the mineral powder is greater than that of the fly ash.
It can be seen from the calculated value of the compression-reduction ratio that the addition of HPMC will effectively lower the compression ratio and improve the flexibility of the mortar, but it is actually at the expense of a substantial reduction in the compressive strength.
In terms of admixtures, as the amount of admixture increases, the compression-fold ratio tends to increase, indicating that the admixture is not conducive to the flexibility of the mortar. In addition, it can be found that the compression-fold ratio of the mortar without HPMC increases with the addition of the admixture. The increase is slightly larger, that is, HPMC can improve the embrittlement of mortar caused by the addition of admixtures to a certain extent.
It can be seen that for the compressive strength of 7d, the adverse effects of the admixtures are no longer obvious. The compressive strength values are roughly the same at each admixture dosage level, and HPMC still has a relatively obvious disadvantage on the compressive strength. effect.
It can be seen that in terms of flexural strength, the admixture has an adverse effect on the 7d flexural resistance as a whole, and only the group of mineral powders performed better, basically maintained at 11-12MPa.
It can be seen that the admixture has an adverse effect in terms of the indentation ratio. With the increase of the amount of the admixture, the indentation ratio gradually increases, that is, the mortar is brittle. HPMC can obviously reduce the compression-fold ratio and improve the brittleness of mortar.
It can be seen that from the 28d compressive strength, the admixture has played a more obvious beneficial effect on the later strength, and the compressive strength has been increased by 3-5MPa, which is mainly due to the micro-filling effect of the admixture and the pozzolanic substance. The secondary hydration effect of the material, on the one hand, can utilize and consume the calcium hydroxide produced by cement hydration (calcium hydroxide is a weak phase in the mortar, and its enrichment in the interface transition zone is detrimental to the strength), generating more More hydration products, on the other hand, promote the hydration degree of cement and make the mortar more dense. HPMC still has a significant adverse effect on the compressive strength, and the weakening strength can reach more than 10MPa. To analyze the reasons, HPMC introduces a certain amount of air bubbles in the mortar mixing process, which reduces the compactness of the mortar body. This is one reason. HPMC is easily adsorbed on the surface of solid particles to form a film, hindering the hydration process, and the interface transition zone is weaker, which is not conducive to strength.
It can be seen that in terms of 28d flexural strength, the data has a larger dispersion than compressive strength, but the adverse effect of HPMC can still be seen.
It can be seen that, from the point of view of the compression-reduction ratio, HPMC is generally beneficial to reduce the compression-reduction ratio and improve the toughness of the mortar. In one group, with the increase of the amount of admixtures, the compression-refraction ratio increases. Analysis of the reasons shows that the admixture has obvious improvement in the later compressive strength, but limited improvement in the later flexural strength, resulting in the compression-refraction ratio. improvement.
4.2 Compressive and flexural strength tests of bonded mortar
In order to explore the influence of cellulose ether and admixture on the compressive and flexural strength of bonded mortar, the experiment fixed the content of cellulose ether HPMC (viscosity 100,000) as 0.30% of the dry weight of the mortar. and compared with the blank group.
Admixtures (fly ash and slag powder) are still tested at 0%, 10%, 20%, and 30%.
4.2.1 Compressive and flexural strength test scheme of bonded mortar
4.2.2 Test results and analysis of the influence of compressive and flexural strength of bonded mortar
It can be seen from the experiment that HPMC is obviously unfavorable in terms of the 28d compressive strength of the bonding mortar, which will cause the strength to decrease by about 5MPa, but the key indicator for judging the quality of the bonding mortar is not the compressive strength, so it is acceptable; When the compound content is 20%, the compressive strength is relatively ideal.
It can be seen from the experiment that from the perspective of flexural strength, the strength reduction caused by HPMC is not large. It may be that the bonding mortar has poor fluidity and obvious plastic characteristics compared with high-fluid mortar. The positive effects of slipperiness and water retention effectively offset some of the negative effects of introducing gas to reduce compactness and interface weakening; admixtures have no obvious effect on flexural strength, and the data of fly ash group fluctuates slightly.
It can be seen from the experiments that, as far as the pressure-reduction ratio is concerned, in general, the increase of the admixture content increases the pressure-reduction ratio, which is unfavorable to the toughness of the mortar; HPMC has a favorable effect, which can reduce the pressure-reduction ratio by O. 5 above, it should be pointed out that, according to "JG 149.2003 Expanded Polystyrene Board Thin Plaster External Wall External Insulation System", there is generally no mandatory requirement for the compression-folding ratio in the detection index of the bonding mortar, and the compression-folding ratio is mainly It is used to limit the brittleness of the plastering mortar, and this index is only used as a reference for the flexibility of the bonding mortar.
4.3 Bonding Strength Test of Bonding Mortar
In order to explore the influence law of the composite application of cellulose ether and admixture on the bond strength of bonded mortar, refer to "JG/T3049.1998 Putty for Building Interior" and "JG 149.2003 Expanded Polystyrene Board Thin Plastering Exterior Walls" Insulation System", we carried out the bond strength test of the bonding mortar, using the bonding mortar ratio in Table 4.2.1, and fixing the content of cellulose ether HPMC (viscosity 100,000) to 0 of the dry weight of the mortar .30%, and compared with the blank group.
Admixtures (fly ash and slag powder) are still tested at 0%, 10%, 20%, and 30%.
4.3.1 Test scheme of bond strength of bond mortar
4.3.2 Test results and analysis of bond strength of bond mortar
(1) 14d bond strength test results of bonding mortar and cement mortar
It can be seen from the experiment that the groups added with HPMC are significantly better than the blank group, indicating that HPMC is beneficial to the bonding strength, mainly because the water retention effect of HPMC protects the water at the bonding interface between the mortar and the cement mortar test block. The bonding mortar at the interface is fully hydrated, thereby increasing the bond strength.
In terms of admixtures, the bond strength is relatively high at a dosage of 10%, and although the hydration degree and speed of the cement can be improved at a high dosage, it will lead to a decrease in the overall hydration degree of the cementitious material, thus causing stickiness. decrease in knot strength.
It can be seen from the experiment that in terms of the test value of the operational time intensity, the data is relatively discrete, and the admixture has little effect, but in general, compared with the original intensity, there is a certain decrease, and the decrease of HPMC is smaller than that of the blank group, indicating that It is concluded that the water retention effect of HPMC is beneficial to the reduction of water dispersion, so that the decrease of mortar bond strength decreases after 2.5h.
(2) 14d bond strength test results of bonding mortar and expanded polystyrene board
It can be seen from the experiment that the test value of the bond strength between the bonding mortar and the polystyrene board is more discrete. In general, it can be seen that the group mixed with HPMC is more effective than the blank group due to better water retention. Well, the incorporation of admixtures reduces the stability of the bond strength test.
4.4 Chapter Summary
1. For high fluidity mortar, with the increase of age, the compressive-fold ratio has an upward trend; the incorporation of HPMC has an obvious effect of reducing the strength (the decrease in the compressive strength is more obvious), which also leads to The decrease of the compression-folding ratio, that is, HPMC has obvious help to the improvement of mortar toughness. In terms of three-day strength, fly ash and mineral powder can make a slight contribution to the strength at 10%, while the strength decreases at high dosage, and the crushing ratio increases with the increase of mineral admixtures; in the seven-day strength, The two admixtures have little effect on the strength, but the overall effect of fly ash strength reduction is still obvious; in terms of the 28-day strength, the two admixtures have contributed to the strength, compressive and flexural strength. Both were slightly increased, but the pressure-fold ratio still increased with the increase of the content.
2. For the 28d compressive and flexural strength of the bonded mortar, when the admixture content is 20%, the compressive and flexural strength performance is better, and the admixture still leads to a small increase in the compressive-fold ratio, reflecting its Adverse effect on the toughness of mortar; HPMC leads to a significant decrease in strength, but can significantly reduce the compression-to-fold ratio.
3. Regarding the bond strength of the bonded mortar, HPMC has a certain favorable influence on the bond strength. The analysis should be that its water retention effect reduces the loss of mortar moisture and ensures more sufficient hydration; The relationship between the content of the mixture is not regular, and the overall performance is better with cement mortar when the content is 10%.
Chapter 5 A Method for Predicting the Compressive Strength of Mortar and Concrete
In this chapter, a method for predicting the strength of cement-based materials based on admixture activity coefficient and FERET strength theory is proposed. We first think of mortar as a special kind of concrete without coarse aggregates.
It is well known that compressive strength is an important indicator for cement-based materials (concrete and mortar) used as structural materials. However, due to many influencing factors, there is no mathematical model that can accurately predict its intensity. This causes certain inconvenience to the design, production and use of mortar and concrete. The existing models of concrete strength have their own advantages and disadvantages: some predict the strength of concrete through the porosity of concrete from the common point of view of the porosity of solid materials; some focus on the influence of the water-binder ratio relationship on the strength. This paper mainly combines the activity coefficient of pozzolanic admixture with Feret's strength theory, and makes some improvements to make it relatively more accurate to predict the compressive strength.
5.1 Feret's Strength Theory
In 1892, Feret established the earliest mathematical model for predicting compressive strength. Under the premise of given concrete raw materials, the formula for predicting concrete strength is proposed for the first time.
The advantage of this formula is that the grout concentration, which correlates with concrete strength, has a well-defined physical meaning. At the same time, the influence of air content is taken into account, and the correctness of the formula can be proved physically. The rationale for this formula is that it expresses information that there is a limit to the concrete strength that can be obtained. The disadvantage is that it ignores the influence of aggregate particle size, particle shape and aggregate type. When predicting the strength of concrete at different ages by adjusting the K value, the relationship between different strength and age is expressed as a set of divergences through the coordinate origin. The curve is inconsistent with the actual situation (especially when the age is longer). Of course, this formula proposed by Feret is designed for the mortar of 10.20MPa. It cannot fully adapt to the improvement of concrete compressive strength and the influence of increasing components due to the progress of mortar concrete technology.
It is considered here that the strength of concrete (especially for ordinary concrete) mainly depends on the strength of the cement mortar in the concrete, and the strength of the cement mortar depends on the density of the cement paste, that is, the volume percentage of the cementitious material in the paste.
The theory is closely related to the effect of void ratio factor on strength. However, because the theory was put forward earlier, the influence of admixture components on concrete strength was not considered. In view of this, this paper will introduce the admixture influence coefficient based on the activity coefficient for partial correction. At the same time, on the basis of this formula, an influence coefficient of porosity on concrete strength is reconstructed.
5.2 Activity coefficient
The activity coefficient, Kp, is used to describe the effect of pozzolanic materials on the compressive strength. Obviously, it depends on the nature of the pozzolanic material itself, but also on the age of the concrete. The principle of determining the activity coefficient is to compare the compressive strength of a standard mortar with the compressive strength of another mortar with pozzolanic admixtures and replacing the cement with the same amount of cement quality (the country p is the activity coefficient test. Use surrogate percentages). The ratio of these two intensities is called the activity coefficient fO), where t is the age of the mortar at the time of testing. If fO) is less than 1, the activity of pozzolan is less than that of cement r. Conversely, if fO) is greater than 1, the pozzolan has a higher reactivity (this usually happens when silica fume is added).
For the commonly used activity coefficient at 28-day compressive strength, according to ((GBT18046.2008 Granulated blast furnace slag powder used in cement and concrete) H90, the activity coefficient of granulated blast furnace slag powder is in standard cement mortar The strength ratio obtained by replacing 50% cement on the basis of the test; according to ((GBT1596.2005 Fly ash used in cement and concrete), the activity coefficient of fly ash is obtained after replacing 30% cement on the basis of the standard cement mortar test According to "GB.T27690.2011 Silica Fume for Mortar and Concrete", the activity coefficient of silica fume is the strength ratio obtained by replacing 10% cement on the basis of standard cement mortar test.
Generally, granulated blast furnace slag powder Kp=0.95～1.10, fly ash Kp=0.7-1.05, silica fume Kp=1.00～1.15. We assume that its effect on strength is independent of cement. That is, the mechanism of the pozzolanic reaction should be controlled by the reactivity of the pozzolan, not by the lime precipitation rate of cement hydration.
5.3 Influence coefficient of admixture on strength
5.4 Influence coefficient of water consumption on strength
5.5 Influence coefficient of aggregate composition on strength
According to the views of professors P K Mehta and P C Aitcin in the United States, in order to achieve the best workability and strength properties of HPC at the same time, the volume ratio of cement slurry to aggregate should be 35:65 [4810] Because of the general plasticity and fluidity The total amount of aggregate of concrete does not change much. As long as the strength of the aggregate base material itself meets the requirements of the specification, the influence of the total amount of aggregate on the strength is ignored, and the overall integral fraction can be determined within 60-70% according to the slump requirements.
It is theoretically believed that the ratio of coarse and fine aggregates will have a certain influence on the strength of concrete. As we all know, the weakest part in concrete is the interface transition zone between aggregate and cement and other cementitious material pastes. Therefore, the final failure of common concrete is due to the initial damage of the interface transition zone under stress caused by factors such as load or temperature change. caused by the continuous development of cracks. Therefore, when the degree of hydration is similar, the larger the interface transition zone is, the easier the initial crack will develop into a long through crack after stress concentration. That is to say, the more coarse aggregates with more regular geometric shapes and larger scales in the interface transition zone, the greater the stress concentration probability of the initial cracks, and the macroscopically manifested that the concrete strength increases with the increase of the coarse aggregate ratio. reduced. However, the above premise is that it is required to be medium sand with very little mud content.
The sand rate also has a certain influence on the slump. Therefore, the sand rate can be preset by the slump requirements, and can be determined within 32% to 46% for ordinary concrete.
The amount and variety of admixtures and mineral admixtures are determined by trial mix. In ordinary concrete, the amount of mineral admixture should be less than 40%, while in high-strength concrete, silica fume should not exceed 10%. The amount of cement should not be greater than 500kg/m3.
5.6 Application of this prediction method to guide mix proportion calculation example
The materials used are as follows:
The cement is E042.5 cement produced by Lubi Cement Factory, Laiwu City, Shandong Province, and its density is 3.19/cm3;
The fly ash is grade II ball ash produced by Jinan Huangtai Power Plant, and its activity coefficient is O. 828, its density is 2.59/cm3;
The silica fume produced by Shandong Sanmei Silicon Material Co., Ltd. has an activity coefficient of 1.10 and a density of 2.59/cm3;
Taian dry river sand has a density of 2.6 g/cm3, a bulk density of 1480kg/m3, and a fineness modulus of Mx=2.8;
Jinan Ganggou produces 5-’25mm dry crushed stone with a bulk density of 1500kg/m3 and a density of about 2.7∥cm3;
The water-reducing agent used is a self-made aliphatic high-efficiency water-reducing agent, with a water-reducing rate of 20%; the specific dosage is determined experimentally according to the requirements of slump. Trial preparation of C30 concrete, the slump is required to be greater than 90mm.
1. formulation strength
2. sand quality
3. Determination of Influence Factors of Each Intensity
4. Ask for water consumption
5. The dosage of water-reducing agent is adjusted according to the requirement of slump. The dosage is 1%, and Ma=4kg is added to the mass.
6. In this way, the calculation ratio is obtained
7. After trial mixing, it can meet the slump requirements. The measured 28d compressive strength is 39.32MPa, which meets the requirements.
5.7 Chapter Summary
In the case of ignoring the interaction of the admixtures I and F, we have discussed the activity coefficient and Feret’s strength theory, and obtained the influence of multiple factors on the strength of concrete:
1 Concrete admixture influence coefficient
2 Influence coefficient of water consumption
3 Influence coefficient of aggregate composition
4 Actual comparison. It is verified that the 28d strength prediction method of concrete improved by the activity coefficient and Feret’s strength theory is in good agreement with the actual situation, and it can be used to guide the preparation of mortar and concrete.
Chapter 6 Conclusion and Outlook
6.1 Main conclusions
The first part comprehensively compares the clean slurry and mortar fluidity test of various mineral admixtures mixed with three kinds of cellulose ethers, and finds the following main rules:
1. Cellulose ether has certain retarding and air-entraining effects. Among them, CMC has a weak water retention effect at low dosage, and has a certain loss over time; while HPMC has a significant water retention and thickening effect, which significantly reduces the fluidity of pure pulp and mortar, and The thickening effect of HPMC with high nominal viscosity is slightly obvious.
2. Among the admixtures, the initial and half-hour fluidity of fly ash on the clean slurry and mortar has been improved to a certain extent. The 30% content of the clean slurry test can be increased by about 30mm; the fluidity of the mineral powder on the clean slurry and mortar There is no obvious rule of influence; although the content of silica fume is low, its unique ultra-fineness, fast reaction, and strong adsorption make it have a significant reduction effect on the fluidity of clean slurry and mortar, especially when mixed with 0.15 When %HPMC, there will be a phenomenon that the cone die cannot be filled. Compared with the test results of the clean slurry, it is found that the effect of the admixture in the mortar test tends to weaken. In terms of controlling bleeding, fly ash and mineral powder are not obvious. Silica fume can significantly reduce the amount of bleeding, but it is not conducive to the reduction of mortar fluidity and loss over time, and it is easy to reduce the operating time.
3. In the respective range of dosage changes, the factors affecting the fluidity of cement-based slurry, the dosage of HPMC and silica fume are the primary factors, both in the control of bleeding and the control of flow state, are relatively obvious. The influence of coal ash and mineral powder is secondary and plays an auxiliary adjustment role.
4. The three kinds of cellulose ethers have a certain air-entraining effect, which will cause bubbles to overflow on the surface of the pure slurry. However, when the content of HPMC reaches more than 0.1%, due to the high viscosity of the slurry, the bubbles cannot be retained in the slurry. overflow. There will be bubbles on the surface of mortar with a fluidity above 250ram, but the blank group without cellulose ether generally has no bubbles or only a very small amount of bubbles, indicating that cellulose ether has a certain air-entraining effect and makes the slurry viscous. In addition, due to the excessive viscosity of the mortar with poor fluidity, it is difficult for the air bubbles to float up by the self-weight effect of the slurry, but is retained in the mortar, and its influence on the strength cannot be ignored.
Part II Mortar Mechanical Properties
1. For high fluidity mortar, with the increase of age, the crushing ratio has an upward trend; the addition of HPMC has a significant effect of reducing the strength (the decrease in the compressive strength is more obvious), which also leads to the crushing The decrease of the ratio, that is, HPMC has obvious help to the improvement of mortar toughness. In terms of three-day strength, fly ash and mineral powder can make a slight contribution to the strength at 10%, while the strength decreases at high dosage, and the crushing ratio increases with the increase of mineral admixtures; in the seven-day strength, The two admixtures have little effect on the strength, but the overall effect of fly ash strength reduction is still obvious; in terms of the 28-day strength, the two admixtures have contributed to the strength, compressive and flexural strength. Both were slightly increased, but the pressure-fold ratio still increased with the increase of the content.
2. For the 28d compressive and flexural strength of the bonded mortar, when the admixture content is 20%, the compressive and flexural strengths are better, and the admixture still leads to a small increase in the compressive-to-fold ratio, reflecting its effect on the mortar. Adverse effects of toughness; HPMC leads to a significant decrease in strength.
3. Regarding the bond strength of bonded mortar, HPMC has a certain favorable effect on the bond strength. The analysis should be that its water retention effect reduces the loss of water in the mortar and ensures more sufficient hydration. The bond strength is related to the admixture. The relationship between the dosage is not regular, and the overall performance is better with cement mortar when the dosage is 10%.
4. CMC is not suitable for cement-based cementitious materials, its water retention effect is not obvious, and at the same time, it makes the mortar more brittle; while HPMC can effectively reduce the compression-to-fold ratio and improve the toughness of mortar, but it is at the expense of a substantial reduction in compressive strength.
5. Comprehensive fluidity and strength requirements, HPMC content of 0.1% is more appropriate. When fly ash is used for structural or reinforced mortar that requires fast hardening and early strength, the dosage should not be too high, and the maximum dosage is about 10%. Requirements; considering factors such as the poor volume stability of mineral powder and silica fume, they should be controlled at 10% and n 3% respectively. The effects of admixtures and cellulose ethers are not significantly correlated, with
have an independent effect.
The third part In the case of ignoring the interaction between admixtures, through the discussion of the activity coefficient of mineral admixtures and Feret’s strength theory, the influence law of multiple factors on the strength of concrete (mortar) is obtained:
1. Mineral Admixture Influence Coefficient
2. Influence coefficient of water consumption
3. Influence factor of aggregate composition
4. The actual comparison shows that the 28d strength prediction method of concrete improved by the activity coefficient and Feret strength theory is in good agreement with the actual situation, and it can be used to guide the preparation of mortar and concrete.
6.2 Deficiencies and Prospects
This paper mainly studies the fluidity and mechanical properties of the clean paste and mortar of the binary cementitious system. The effect and influence of the joint action of multi-component cementitious materials need to be further studied. In the test method, mortar consistency and stratification can be used. The effect of cellulose ether on the consistency and water retention of mortar is studied by the degree of cellulose ether. In addition, the microstructure of mortar under the compound action of cellulose ether and mineral admixture is also to be studied.
Cellulose ether is now one of the indispensable admixture components of various mortars. Its good water retention effect prolongs the operating time of the mortar, makes the mortar have good thixotropy, and improves the toughness of the mortar. It is convenient for construction; and the application of fly ash and mineral powder as an industrial waste in mortar can also create great economic and environmental benefits
Chapter 1 Introduction
1.1 commodity mortar
1.1.1 Introduction of commercial mortar
In my country’s building materials industry, concrete has achieved a high degree of commercialization, and the commercialization of mortar is also getting higher and higher, especially for various special mortars, manufacturers with higher technical capabilities are required to ensure the various mortars. The performance indicators are qualified. Commercial mortar is divided into two categories: ready-mixed mortar and dry-mixed mortar. Ready-mixed mortar means that the mortar is transported to the construction site after being mixed with water by the supplier in advance according to the project requirements, while dry-mixed mortar is made by the mortar manufacturer by dry-mixing and packaging cementitious materials, aggregates and additives according to a certain ratio. Add a certain amount of water to the construction site and mix it before use.
Traditional mortar has many weaknesses in use and performance. For example, the stacking of raw materials and on-site mixing cannot meet the requirements of civilized construction and environmental protection. In addition, due to on-site construction conditions and other reasons, it is easy to make the quality of mortar difficult to guarantee, and it is impossible to obtain high performance. mortar. Compared with traditional mortar, commercial mortar has some obvious advantages. First of all, its quality is easy to control and guarantee, its performance is superior, its types are refined, and it is better targeted to engineering requirements. European dry-mixed mortar has been developed in the 1950s, and my country is also vigorously advocating the application of commercial mortar. Shanghai has already used commercial mortar in 2004. With the continuous development of my country’s urbanization process, at least in the urban market, it will be inevitable that commercial mortar with various advantages will replace traditional mortar.
1.1.2 Problems existing in commercial mortar
Although commercial mortar has many advantages over traditional mortar, there are still many technical difficulties as mortar. High fluidity mortar, such as reinforcement mortar, cement-based grouting materials, etc., have extremely high requirements on strength and work performance, so the use of superplasticizers is large, which will cause serious bleeding and affect the mortar. Comprehensive performance; and for some plastic mortars, because they are very sensitive to the loss of water, it is easy to have a serious decrease in workability due to the loss of water in a short time after mixing, and the operation time is extremely short: In addition, for In terms of bonding mortar, the bonding matrix is often relatively dry. During the construction process, due to the insufficient ability of the mortar to retain water, a large amount of water will be absorbed by the matrix, resulting in local water shortage of the bonding mortar and insufficient hydration. The phenomenon that the strength decreases and the adhesive force decreases.
In response to the above questions, an important additive, cellulose ether, is widely used in mortar. As a kind of etherified cellulose, cellulose ether has affinity for water, and this polymer compound has excellent water absorption and water retention ability, which can well solve the bleeding of mortar, short operation time, stickiness, etc. Insufficient knot strength and many other problems.
In addition, admixtures as partial substitutes for cement, such as fly ash, granulated blast furnace slag powder (mineral powder), silica fume, etc., are now more and more important. We know that most of the admixtures are by-products of industries such as electric power, smelting steel, smelting ferrosilicon and industrial silicon. If they cannot be fully utilized, the accumulation of admixtures will occupy and destroy a large amount of land and cause serious damage. environmental pollution. On the other hand, if admixtures are used reasonably, some properties of concrete and mortar can be improved, and some engineering problems in the application of concrete and mortar can be well solved. Therefore, the wide application of admixtures is beneficial to the environment and industry. are beneficial.
1.2 Cellulose ethers
Cellulose ether (cellulose ether) is a polymer compound with ether structure produced by etherification of cellulose. Each glucosyl ring in cellulose macromolecules contains three hydroxyl groups, a primary hydroxyl group on the sixth carbon atom, a secondary hydroxyl group on the second and third carbon atoms, and the hydrogen in the hydroxyl group is replaced by a hydrocarbon group to generate cellulose ether derivatives. thing. Cellulose is a polyhydroxy polymer compound that neither dissolves nor melts, but cellulose can be dissolved in water, dilute alkali solution and organic solvent after etherification, and has a certain thermoplasticity.
Cellulose ether takes natural cellulose as raw material and is prepared by chemical modification. It is classified into two categories: ionic and non-ionic in ionized form. It is widely used in chemical, petroleum, construction, medicine, ceramics and other industries. .
1.2.1 Classification of cellulose ethers for construction
Cellulose ether for construction is a general term for a series of products produced by the reaction of alkali cellulose and etherifying agent under certain conditions. Different kinds of cellulose ethers can be obtained by replacing alkali cellulose with different etherifying agents.
1. According to the ionization properties of the substituents, cellulose ethers can be divided into two categories: ionic (such as carboxymethyl cellulose) and non-ionic (such as methyl cellulose).
2. According to the types of substituents, cellulose ethers can be divided into single ethers (such as methyl cellulose) and mixed ethers (such as hydroxypropyl methyl cellulose).
3. According to different solubility, it is divided into water-soluble (such as hydroxyethyl cellulose) and organic solvent solubility (such as ethyl cellulose), etc. The main application type in dry-mixed mortar is water-soluble cellulose, while water-soluble cellulose It is divided into instant type and delayed dissolution type after surface treatment.
1.2.2 Explanation of the mechanism of action of cellulose ether in mortar
Cellulose ether is a key admixture to improve the water retention properties of dry-mixed mortar, and it is also one of the key admixtures to determine the cost of dry-mixed mortar materials.
1. After the cellulose ether in the mortar is dissolved in water, the unique surface activity ensures that the cementitious material is effectively and uniformly dispersed in the slurry system, and cellulose ether, as a protective colloid, can “encapsulate” solid particles, Thus, a lubricating film is formed on the outer surface, and the lubricating film can make the mortar body have good thixotropy. That is to say, the volume is relatively stable in the standing state, and there will be no adverse phenomena such as bleeding or stratification of light and heavy substances, which makes the mortar system more stable; while in the agitated construction state, the cellulose ether will play a role in reducing the shearing of the slurry. The effect of variable resistance makes the mortar have good fluidity and smoothness during construction during the mixing process.
2. Due to the characteristics of its own molecular structure, the cellulose ether solution can keep water and not easily lost after being mixed into the mortar, and will be gradually released in a long period of time, which prolongs the operation time of the mortar and gives the mortar good water retention and operability.
1.2.3 Several important construction grade cellulose ethers
1. Methyl Cellulose (MC)
After the refined cotton is treated with alkali, methyl chloride is used as the etherifying agent to make cellulose ether through a series of reactions. The general substitution degree is 1. Melting 2.0, the degree of substitution is different and the solubility is also different. Belongs to non-ionic cellulose ether.
2. Hydroxyethyl Cellulose (HEC)
It is prepared by reacting with ethylene oxide as an etherifying agent in the presence of acetone after the refined cotton is treated with alkali. The degree of substitution is generally 1.5 to 2.0. It has strong hydrophilicity and is easy to absorb moisture.
3. Hydroxypropyl methylcellulose (HPMC)
Hydroxypropyl methylcellulose is a cellulose variety whose output and consumption are rapidly increasing in recent years. It is a non-ionic cellulose mixed ether made from refined cotton after alkali treatment, using propylene oxide and methyl chloride as etherifying agents, and through a series of reactions. The degree of substitution is generally 1.2 to 2.0. Its properties vary according to the ratio of methoxyl content and hydroxypropyl content.
4. Carboxymethylcellulose (CMC)
Ionic cellulose ether is prepared from natural fibers (cotton, etc.) after alkali treatment, using sodium monochloroacetate as an etherifying agent, and through a series of reaction treatments. The degree of substitution is generally 0.4–d. 4. Its performance is greatly affected by the degree of substitution.
Among them, the third and fourth types are the two types of cellulose used in this experiment.
1.2.4 Development Status of Cellulose Ether Industry
After years of development, the cellulose ether market in developed countries has become very mature, and the market in developing countries is still in the growth stage, which will become the main driving force for the growth of global cellulose ether consumption in the future. At present, the total global production capacity of cellulose ether exceeds 1 million tons, with Europe accounting for 35% of the total global consumption, followed by Asia and North America. Carboxymethyl cellulose ether (CMC) is the main consumer species, accounting for 56% of the total, followed by methyl cellulose ether (MC/HPMC) and hydroxyethyl cellulose ether (HEC), accounting for 56% of the total. 25% and 12%. The foreign cellulose ether industry is highly competitive. After many integrations, the output is mainly concentrated in several large companies, such as Dow Chemical Company and Hercules Company in the United States, Akzo Nobel in the Netherlands, Noviant in Finland and DAICEL in Japan, etc. .
my country is the world’s largest producer and consumer of cellulose ether, with an average annual growth rate of more than 20%. According to preliminary statistics, there are about 50 cellulose ether production enterprises in China. The designed production capacity of the cellulose ether industry has exceeded 400,000 tons, and there are about 20 enterprises with a capacity of more than 10,000 tons, mainly located in Shandong, Hebei, Chongqing and Jiangsu. , Zhejiang, Shanghai and other places. In 2011, China’s CMC production capacity was about 300,000 tons. With the increasing demand for high-quality cellulose ethers in the pharmaceutical, food, daily chemical and other industries in recent years, the domestic demand for other cellulose ether products other than CMC is increasing. Larger, the capacity of MC/HPMC is about 120,000 tons, and the capacity of HEC is about 20,000 tons. PAC is still in the stage of promotion and application in China. With the development of large offshore oil fields and the development of building materials, food, chemical and other industries, the amount and field of PAC are increasing and expanding year by year, with a production capacity of more than 10,000 tons.
1.3 Research on the application of cellulose ether to mortar
Regarding the engineering application research of cellulose ether in the construction industry, domestic and foreign scholars have conducted a large number of experimental research and mechanism analysis.
1.3.1 Brief introduction of foreign research on the application of cellulose ether to mortar
Laetitia Patural, Philippe Marchal and others in France pointed out that cellulose ether has a significant effect on the water retention of mortar, and the structural parameter is the key, and the molecular weight is the key to control the water retention and consistency. With the increase of molecular weight, the yield stress decreases, the consistency increases, and the water retention performance increases; on the contrary, the molar substitution degree (related to the content of hydroxyethyl or hydroxypropyl) has little effect on the water retention of dry-mixed mortar. However, cellulose ethers with low molar degrees of substitution have improved water retention.
An important conclusion about the water retention mechanism is that the rheological properties of the mortar are critical. It can be seen from the test results that for dry-mixed mortar with a fixed water-cement ratio and admixture content, the water retention performance generally has the same regularity as its consistency. However, for some cellulose ethers, the trend is not obvious; in addition, for starch ethers, there is an opposite pattern. The viscosity of the fresh mix is not the only parameter for determining water retention.
Laetitia Patural, Patrice Potion, et al., with the help of pulsed field gradient and MRI techniques, found that the moisture migration at the interface of mortar and unsaturated substrate is affected by the addition of a small amount of CE. The loss of water is due to capillary action rather than water diffusion. Moisture migration by capillary action is governed by substrate micropore pressure, which in turn is determined by micropore size and Laplace theory interfacial tension, as well as fluid viscosity. This indicates that the rheological properties of CE aqueous solution are the key to water retention performance. However, this hypothesis contradicts some consensus (other tackifiers like high molecular polyethylene oxide and starch ethers are not as effective as CE).
Jean. Yves Petit, Erie Wirquin et al. used cellulose ether through experiments, and its 2% solution viscosity was from 5000 to 44500mpa. S ranging from MC and HEMC. Find:
1. For a fixed amount of CE, the type of CE has a great influence on the viscosity of the adhesive mortar for tiles. This is due to the competition between CE and dispersible polymer powder for the adsorption of cement particles.
2. The competitive adsorption of CE and rubber powder has a significant effect on the setting time and spalling when the construction time is 20-30min.
3. The bond strength is affected by the pairing of CE and rubber powder. When the CE film cannot prevent the evaporation of moisture at the interface of the tile and the mortar, the adhesion under high temperature curing decreases.
4. The coordination and interaction of CE and dispersible polymer powder should be taken into consideration when designing the proportion of adhesive mortar for tiles.
Germany’s LSchmitzC. J. Dr. H(a)cker mentioned in the article that HPMC and HEMC in cellulose ether have a very critical role in water retention in dry-mixed mortar. In addition to ensuring the enhanced water retention index of cellulose ether, it is recommended to use modified Cellulose ethers are used to improve and improve the working properties of mortar and the properties of dry and hardened mortar.
1.3.2 Brief introduction of domestic research on the application of cellulose ether to mortar
Xin Quanchang from Xi’an University of Architecture and Technology studied the influence of various polymers on some properties of bonding mortar, and found that the composite use of dispersible polymer powder and hydroxyethyl methyl cellulose ether can not only improve the performance of bonding mortar, but also can Part of the cost is reduced; the test results show that when the content of redispersible latex powder is controlled at 0.5%, and the content of hydroxyethyl methyl cellulose ether is controlled at 0.2%, the prepared mortar is resistant to bending. and bonding strength are more prominent, and have good flexibility and plasticity.
Professor Ma Baoguo from Wuhan University of Technology pointed out that cellulose ether has obvious retardation effect, and can affect the structural form of hydration products and the pore structure of cement slurry; cellulose ether is mainly adsorbed on the surface of cement particles to form a certain barrier effect. It hinders the nucleation and growth of hydration products; on the other hand, cellulose ether hinders the migration and diffusion of ions due to its obvious viscosity increasing effect, thereby delaying the hydration of cement to a certain extent; cellulose ether has alkali stability.
Jian Shouwei from Wuhan University of Technology concluded that the role of CE in mortar is mainly reflected in three aspects: excellent water retention capacity, influence on mortar consistency and thixotropy, and adjustment of rheology. CE not only gives mortar good working performance, but also To reduce the early hydration heat release of cement and delay the hydration kinetic process of cement, of course, based on the different use cases of mortar, there are also differences in its performance evaluation methods.
CE modified mortar is applied in the form of thin-layer mortar in daily dry-mix mortar (such as brick binder, putty, thin-layer plastering mortar, etc.). This unique structure is usually accompanied by the rapid water loss of the mortar. At present, the main research focuses on the face tile adhesive, and there is less research on other types of thin-layer CE modified mortar.
Su Lei from Wuhan University of Technology obtained through the experimental analysis of the water retention rate, water loss and setting time of the mortar modified with cellulose ether. The amount of water decreases gradually, and the coagulation time is prolonged; when the amount of water reaches O. After 6%, the change of water retention rate and water loss is no longer obvious, and the setting time is nearly doubled; and the experimental study of its compressive strength shows that when the content of cellulose ether is lower than 0.8%, the content of cellulose ether is less than 0.8%. The increase will significantly reduce the compressive strength; and in terms of the bonding performance with the cement mortar board, O. Below 7% of the content, the increase of the content of cellulose ether can effectively improve the bonding strength.
Lai Jianqing of Xiamen Hongye Engineering Construction Technology Co., Ltd. analyzed and concluded that the optimal dosage of cellulose ether when considering the water retention rate and consistency index is 0 through a series of tests on the water retention rate, strength and bond strength of EPS thermal insulation mortar. 2%; cellulose ether has a strong air-entraining effect, which will cause a decrease in strength, especially a decrease in tensile bond strength, so it is recommended to use it together with redispersible polymer powder.
Yuan Wei and Qin Min of Xinjiang Building Materials Research Institute conducted the test and application research of cellulose ether in foamed concrete. The test results show that HPMC improves the water retention performance of fresh foam concrete and reduces the water loss rate of hardened foam concrete; HPMC can reduce the slump loss of fresh foam concrete and reduce the sensitivity of the mixture to temperature. ; HPMC will significantly reduce the compressive strength of foam concrete. Under natural curing conditions, a certain amount of HPMC can improve the strength of the specimen to a certain extent.
Li Yuhai of Wacker Polymer Materials Co., Ltd. pointed out that the type and amount of latex powder, the type of cellulose ether and the curing environment have a significant impact on the impact resistance of plastering mortar. The effect of cellulose ethers on impact strength is also negligible compared to polymer content and curing conditions.
Yin Qingli of AkzoNobel Specialty Chemicals (Shanghai) Co., Ltd. used Bermocoll PADl, a specially modified polystyrene board bonding cellulose ether, for the experiment, which is especially suitable for the bonding mortar of EPS external wall insulation system. Bermocoll PADl can improve the bonding strength between mortar and polystyrene board in addition to all the functions of cellulose ether. Even in the case of low dosage, it can not only improve the water retention and workability of the fresh mortar, but also can significantly improve the original bonding strength and water-resistant bonding strength between the mortar and the polystyrene board due to the unique anchoring technology. . However, it cannot improve the impact resistance of mortar and the bonding performance with polystyrene board. To improve these properties, redispersible latex powder should be used.
Wang Peiming from Tongji University analyzed the development history of commercial mortar and pointed out that cellulose ether and latex powder have a non-negligible impact on the performance indicators such as water retention, flexural and compressive strength, and elastic modulus of dry powder commercial mortar.
Zhang Lin and others of Shantou Special Economic Zone Longhu Technology Co., Ltd. have concluded that, in the bonding mortar of the expanded polystyrene board thin plastering external wall external thermal insulation system (ie Eqos system), it is recommended that the optimum amount of rubber powder be 2.5% is the limit; low viscosity, highly modified cellulose ether is of great help to the improvement of the auxiliary tensile bond strength of hardened mortar.
Zhao Liqun of Shanghai Institute of Building Research (Group) Co., Ltd. pointed out in the article that cellulose ether can significantly improve the water retention of mortar, and also significantly reduce the bulk density and compressive strength of mortar, and prolong the setting time of mortar. Under the same dosage conditions, cellulose ether with high viscosity is beneficial to the improvement of water retention rate of mortar, but the compressive strength decreases more greatly and the setting time is longer. Thickening powder and cellulose ether eliminate plastic shrinkage cracking of mortar by improving the water retention of mortar.
Fuzhou University Huang Lipin et al studied the doping of hydroxyethyl methyl cellulose ether and ethylene. Physical properties and cross-sectional morphology of modified cement mortar of vinyl acetate copolymer latex powder. It is found that cellulose ether has excellent water retention, water absorption resistance and outstanding air-entraining effect, while the water-reducing properties of latex powder and the improvement of the mechanical properties of mortar are particularly prominent. Modification effect; and there is a suitable dosage range between polymers.
Through a series of experiments, Chen Qian and others from Hubei Baoye Construction Industrialization Co., Ltd. proved that extending the stirring time and increasing the stirring speed can give full play to the role of cellulose ether in the ready-mixed mortar, improve the workability of the mortar, and improve the stirring time. Too short or too slow speed will make the mortar difficult to construct; choosing the right cellulose ether can also improve the workability of ready-mixed mortar.
Li Sihan from Shenyang Jianzhu University and others found that mineral admixtures can reduce the dry shrinkage deformation of mortar and improve its mechanical properties; the ratio of lime to sand has an effect on the mechanical properties and shrinkage rate of mortar; redispersible polymer powder can improve the mortar. Crack resistance, improve adhesion, flexural strength, cohesion, impact resistance and wear resistance, improve water retention and workability; cellulose ether has air-entraining effect, which can improve the water retention of mortar; wood fiber can improve mortar Improve the ease of use, operability, and anti-slip performance, and speed up construction. By adding various admixtures for modification, and through a reasonable ratio, crack-resistant mortar for external wall thermal insulation system with excellent performance can be prepared.
Yang Lei of Henan University of Technology mixed HEMC into the mortar and found that it has the dual functions of water retention and thickening, which prevents the air-entrained concrete from quickly absorbing the water in the plastering mortar, and ensures that the cement in the mortar is fully hydrated, making the mortar The combination with aerated concrete is denser and the bond strength is higher; it can greatly reduce the delamination of plastering mortar for aerated concrete. When HEMC was added to the mortar, the flexural strength of the mortar decreased slightly, while the compressive strength decreased greatly, and the fold-compression ratio curve showed an upward trend, indicating that the addition of HEMC could improve the toughness of the mortar.
Li Yanling and others from Henan University of Technology found that the mechanical properties of the bonded mortar were improved compared with ordinary mortar, especially the bond strength of the mortar, when the compound admixture was added (the content of cellulose ether was 0.15%). It is 2.33 times that of ordinary mortar.
Ma Baoguo from Wuhan University of Technology and others studied the effects of different dosages of styrene-acrylic emulsion, dispersible polymer powder, and hydroxypropyl methylcellulose ether on the water consumption, bond strength and toughness of thin plastering mortar. , found that when the content of styrene-acrylic emulsion was 4% to 6%, the bond strength of mortar reached the best value, and the compression-folding ratio was the smallest; the content of cellulose ether increased to O. At 4%, the bond strength of mortar reaches saturation, and the compression-folding ratio is the smallest; when the content of rubber powder is 3%, the bonding strength of mortar is the best, and the compression-folding ratio decreases with the addition of rubber powder. trend.
Li Qiao and others of Shantou Special Economic Zone Longhu Technology Co., Ltd. pointed out in the article that the functions of cellulose ether in cement mortar are water retention, thickening, air entrainment, retardation and improvement of tensile bond strength, etc. These functions correspond to When examining and selecting MC, the indicators of MC that need to be considered include viscosity, degree of etherification substitution, degree of modification, product stability, effective substance content, particle size and other aspects. When choosing MC in different mortar products, the performance requirements for MC itself should be put forward according to the construction and use requirements of specific mortar products, and the appropriate MC varieties should be selected in combination with the composition and basic index parameters of MC.
Qiu Yongxia of Beijing Wanbo Huijia Science and Trade Co., Ltd. found that with the increase of the viscosity of cellulose ether, the water retention rate of the mortar increased; the finer the particles of cellulose ether, the better the water retention; The higher the water retention rate of cellulose ether; the water retention of cellulose ether decreases with the increase of mortar temperature.
Zhang Bin of Tongji University and others pointed out in the article that the working characteristics of modified mortar are closely related to the viscosity development of cellulose ethers, not that the cellulose ethers with high nominal viscosity have obvious influence on the working characteristics, because they are also affected by the particle size. , dissolution rate and other factors.
Zhou Xiao and others from the Institute of Cultural Relics Protection Science and Technology, China Cultural Heritage Research Institute studied the contribution of two additives, polymer rubber powder and cellulose ether, to the bond strength in NHL (hydraulic lime) mortar system, and found that the simple Due to the excessive shrinkage of hydraulic lime, it cannot produce sufficient tensile strength with the stone interface. An appropriate amount of polymer rubber powder and cellulose ether can effectively improve the bonding strength of NHL mortar and meet the requirements of cultural relic reinforcement and protection materials; in order to prevent It has an impact on the water permeability and breathability of NHL mortar itself and the compatibility with masonry cultural relics. At the same time, considering the initial bonding performance of NHL mortar, the ideal addition amount of polymer rubber powder is below 0.5% to 1%, and the addition of cellulose ether The amount is controlled at about 0.2%.
Duan Pengxuan and others from the Beijing Institute of Building Materials Science made two self-made rheological testers on the basis of establishing the rheological model of fresh mortar, and conducted rheological analysis of ordinary masonry mortar, plastering mortar and plastering gypsum products. The denaturation was measured, and it was found that hydroxyethyl cellulose ether and hydroxypropyl methyl cellulose ether have better initial viscosity value and viscosity reduction performance with time and speed increase, which can enrich the binder for better bonding type, thixotropy and slip resistance.
Li Yanling of Henan University of Technology and others found that the addition of cellulose ether in the mortar can greatly improve the water retention performance of the mortar, thereby ensuring the progress of cement hydration. Although the addition of cellulose ether reduces the flexural strength and compressive strength of the mortar, it still increases the flexural-compression ratio and the bond strength of the mortar to a certain extent.
1.4 Research on the application of admixtures to mortar at home and abroad
In today’s construction industry, the production and consumption of concrete and mortar is huge, and the demand for cement is also increasing. The production of cement is a high energy consumption and high pollution industry. Saving cement is of great significance to control costs and protect the environment. As a partial substitute for cement, mineral admixture can not only optimize the performance of mortar and concrete, but also save a lot of cement under the condition of reasonable utilization.
In the building materials industry, the application of admixtures has been very extensive. Many cement varieties contain more or less a certain amount of admixtures. Among them, the most widely used ordinary Portland cement is added 5% in the production. ~20% admixture. In the production process of various mortar and concrete production enterprises, the application of admixtures is more extensive.
For the application of admixtures in mortar, long-term and extensive research has been carried out at home and abroad.
1.4.1 Brief introduction of foreign research on admixture applied to mortar
P. University of California. J. M. Momeiro Joe IJ K. Wang et al. found that in the hydration process of the gelling material, the gel is not swelled in equal volume, and the mineral admixture can change the composition of the hydrated gel, and found that the swelling of the gel is related to the divalent cations in the gel. The number of copies showed a significant negative correlation.
Kevin J. of the United States. Folliard and Makoto Ohta et al. pointed out that the addition of silica fume and rice husk ash to the mortar can significantly improve the compressive strength, while the addition of fly ash reduces the strength, especially in the early stage.
Philippe Lawrence and Martin Cyr of France found that a variety of mineral admixtures can improve the mortar strength under the appropriate dosage. The difference between different mineral admixtures is not obvious in the early stage of hydration. In the later stage of hydration, the additional strength increase is affected by the activity of the mineral admixture, and the strength increase caused by the inert admixture cannot simply be regarded as filling. effect, but should be attributed to the physical effect of multiphase nucleation.
Bulgaria’s ValIly0 Stoitchkov Stl Petar Abadjiev and others found that the basic components are silica fume and low-calcium fly ash through the physical and mechanical properties of cement mortar and concrete mixed with active pozzolanic admixtures, which can improve the strength of cement stone. Silica fume has a significant effect on the early hydration of cementitious materials, while the fly ash component has an important effect on the later hydration.
1.4.2 Brief introduction of domestic research on the application of admixtures to mortar
Through experimental research, Zhong Shiyun and Xiang Keqin of Tongji University found that the composite modified mortar of a certain fineness of fly ash and polyacrylate emulsion (PAE), when the poly-binder ratio was fixed at 0.08, the compression-folding ratio of the mortar increased with the The fineness and content of fly ash decrease with the increase of fly ash. It is proposed that the addition of fly ash can effectively solve the problem of high cost of improving the flexibility of mortar by simply increasing the content of polymer.
Wang Yinong of Wuhan Iron and Steel Civil Construction Company has studied a high-performance mortar admixture, which can effectively improve the workability of mortar, reduce the degree of delamination, and improve the bonding ability. It is suitable for masonry and plastering of aerated concrete blocks. .
Chen Miaomiao and others from Nanjing University of Technology studied the effect of double mixing fly ash and mineral powder in dry mortar on the working performance and mechanical properties of mortar, and found that the addition of two admixtures not only improved the working performance and mechanical properties of the mixture. The physical and mechanical properties can also effectively reduce the cost. The recommended optimal dosage is to replace 20% of fly ash and mineral powder respectively, the ratio of mortar to sand is 1:3, and the ratio of water to material is 0.16.
Zhuang Zihao from South China University of Technology fixed the water-binder ratio, modified bentonite, cellulose ether and rubber powder, and studied the properties of the mortar strength, water retention and dry shrinkage of three mineral admixtures, and found that the admixture content reached At 50%, the porosity increases significantly and the strength decreases, and the optimal proportion of the three mineral admixtures is 8% limestone powder, 30% slag, and 4% fly ash, which can achieve water retention. rate, the preferred value of intensity.
Li Ying from Qinghai University conducted a series of tests of mortar mixed with mineral admixtures, and concluded and analyzed that mineral admixtures can optimize the secondary particle gradation of powders, and the micro-filling effect and secondary hydration of admixtures can To a certain extent, the compactness of the mortar is increased, thereby increasing its strength.
Zhao Yujing of Shanghai Baosteel New Building Materials Co., Ltd. used the theory of fracture toughness and fracture energy to study the influence of mineral admixtures on the brittleness of concrete. The test shows that the mineral admixture can slightly improve the fracture toughness and fracture energy of mortar; in the case of the same type of admixture, the replacement amount of 40% of the mineral admixture is the most beneficial to the fracture toughness and fracture energy.
Xu Guangsheng of Henan University pointed out that when the specific surface area of the mineral powder is less than E350m2/l [g, the activity is low, the 3d strength is only about 30%, and the 28d strength develops to 0~90%; while at 400m2 melon g, the 3d strength It can be close to 50%, and the 28d strength is above 95%. From the perspective of basic principles of rheology, according to the experimental analysis of mortar fluidity and flow velocity, several conclusions are drawn: fly ash content below 20% can effectively improve mortar fluidity and flow velocity, and mineral powder in When the dosage is below 25%, the fluidity of the mortar can be increased but the flow rate is reduced.
Professor Wang Dongmin of China University of Mining and Technology and Professor Feng Lufeng of Shandong Jianzhu University pointed out in the article that concrete is a three-phase material from the perspective of composite materials, namely cement paste, aggregate, cement paste and aggregate. The interface transition zone ITZ (Interfacial Transition Zone) at the junction. ITZ is a water-rich area, the local water-cement ratio is too large, the porosity after hydration is large, and it will cause the enrichment of calcium hydroxide. This area is most likely to cause initial cracks, and it is most likely to cause stress. Concentration largely determines the intensity. The experimental study shows that the addition of admixtures can effectively improve the endocrine water in the interface transition zone, reduce the thickness of the interface transition zone, and improve the strength.
Zhang Jianxin of Chongqing University and others found that by comprehensive modification of methyl cellulose ether, polypropylene fiber, redispersible polymer powder, and admixtures, a dry-mixed plastering mortar with good performance can be prepared. Dry-mixed crack-resistant plastering mortar has good workability, high bond strength and good crack resistance. The quality of drums and cracks is a common problem.
Ren Chuanyao of Zhejiang University and others studied the effect of hydroxypropyl methylcellulose ether on the properties of fly ash mortar, and analyzed the relationship between wet density and compressive strength. It was found that adding hydroxypropyl methyl cellulose ether into fly ash mortar can significantly improve the water retention performance of mortar, prolong the bonding time of mortar, and reduce the wet density and compressive strength of mortar. There is a good correlation between wet density and 28d compressive strength. Under the condition of known wet density, the 28d compressive strength can be calculated by using the fitting formula.
Professor Pang Lufeng and Chang Qingshan of Shandong Jianzhu University used the uniform design method to study the influence of the three admixtures of fly ash, mineral powder and silica fume on the strength of concrete, and put forward a prediction formula with certain practical value through regression analysis. , and its practicability was verified.
Purpose and significance of this study
As an important water-retaining thickener, cellulose ether is widely used in food processing, mortar and concrete production and other industries. As an important admixture in various mortars, a variety of cellulose ethers can significantly reduce the bleeding of high fluidity mortar, enhance the thixotropy and construction smoothness of the mortar, and improve the water retention performance and bond strength of the mortar.
The application of mineral admixtures is increasingly widespread, which not only solves the problem of processing a large number of industrial by-products, saves land and protects the environment, but also can turn waste into treasure and create benefits.
There have been many studies on the components of the two mortars at home and abroad, but there are not many experimental studies that combine the two together. The purpose of this paper is to mix several cellulose ethers and mineral admixtures into the cement paste at the same time , high fluidity mortar and plastic mortar (taking the bonding mortar as an example), through the exploration test of fluidity and various mechanical properties, the influence law of the two kinds of mortars when the components are added together is summarized, which will affect the future cellulose ether. And the further application of mineral admixtures provides a certain reference.
In addition, this paper proposes a method for predicting the strength of mortar and concrete based on the FERET strength theory and the activity coefficient of mineral admixtures, which can provide a certain guiding significance for the mix ratio design and strength prediction of mortar and concrete.
1.6 The main research content of this paper
The main research contents of this paper include:
1. By compounding several cellulose ethers and various mineral admixtures, experiments on the fluidity of clean slurry and high-fluidity mortar were carried out, and the influence laws were summarized and the reasons were analyzed.
2. By adding cellulose ethers and various mineral admixtures to high fluidity mortar and bonding mortar, explore their effects on compressive strength, flexural strength, compression-folding ratio and bonding mortar of high fluidity mortar and plastic mortar The law of influence on the tensile bond strength.
3. Combined with the FERET strength theory and the activity coefficient of mineral admixtures, a strength prediction method for multi-component cementitious material mortar and concrete is proposed.
Chapter 2 Analysis of raw materials and their components for testing
2.1 Test materials
2.1.1 Cement (C)
The test used the “Shanshui Dongyue” brand PO. 42.5 Cement.
2.1.2 Mineral powder (KF)
The $95 grade granulated blast furnace slag powder from Shandong Jinan Luxin New Building Materials Co., Ltd. was selected.
2.1.3 Fly Ash (FA)
The grade II fly ash produced by Jinan Huangtai Power Plant is selected, the fineness (remaining sieve of 459m square hole sieve) is 13%, and the water demand ratio is 96%.
2.1.4 Silica fume (sF)
Silica fume adopts the silica fume of Shanghai Aika Silica Fume Material Co., Ltd., its density is 2.59/cm3; the specific surface area is 17500m2/kg, and the average particle size is O. 1～0.39m, 28d activity index is 108%, water demand ratio is 120%.
2.1.5 Redispersible latex powder (JF)
The rubber powder adopts Max redispersible latex powder 6070N (bonding type) from Gomez Chemical China Co., Ltd.
2.1.6 Cellulose ether (CE)
CMC adopts coating grade CMC from Zibo Zou Yongning Chemical Co., Ltd., and HPMC adopts two kinds of hydroxypropyl methylcellulose from Gomez Chemical China Co., Ltd.
2.1.7 Other admixtures
Heavy calcium carbonate, wood fiber, water repellent, calcium formate, etc.
2.1,8 quartz sand
The machine-made quartz sand adopts four kinds of fineness: 10-20 mesh, 20-40 H, 40.70 mesh and 70.140 H, the density is 2650 kg/rn3, and the stack combustion is 1620 kg/m3.
2.1.9 Polycarboxylate superplasticizer powder (PC)
The polycarboxylate powder of Suzhou Xingbang Chemical Building Materials Co., Ltd.) is 1J1030, and the water reduction rate is 30%.
2.1.10 Sand (S)
The medium sand of Dawen River in Tai’an is used.
2.1.11 Coarse aggregate (G)
Use Jinan Ganggou to produce 5″ ~ 25 crushed stone.
2.2 Test method
2.2.1 Test method for slurry fluidity
Test equipment: NJ. 160 type cement slurry mixer, produced by Wuxi Jianyi Instrument Machinery Co., Ltd.
The test methods and results are calculated according to the test method for the fluidity of cement paste in Appendix A of “GB 50119.2003 Technical Specifications for the Application of Concrete Admixtures” or ((GB/T8077–2000 Test Method for Homogeneousness of Concrete Admixtures).
2.2.2 Test method for fluidity of high fluidity mortar
Test equipment: JJ. Type 5 cement mortar mixer, produced by Wuxi Jianyi Instrument Machinery Co., Ltd.;
TYE-2000B mortar compression testing machine, produced by Wuxi Jianyi Instrument Machinery Co., Ltd.;
TYE-300B mortar bending test machine, produced by Wuxi Jianyi Instrument Machinery Co., Ltd.
Mortar fluidity detection method is based on “JC. T 986-2005 Cement-based grouting materials” and “GB 50119-2003 Technical Specifications for the Application of Concrete Admixtures” Appendix A, the size of the cone die used, the height is 60mm, the inner diameter of the upper port is 70mm, the inner diameter of the lower port is 100mm, and the outer diameter of the lower port is 120mm, and the total dry weight of the mortar should not be less than 2000g each time.
The test results of the two fluidities should take the average value of the two vertical directions as the final result.
2.2.3 Test method for tensile bond strength of bonded mortar
Main test equipment: WDL. Type 5 electronic universal testing machine, produced by Tianjin Gangyuan Instrument Factory.
The test method for tensile bond strength shall be implemented with reference to Section 10 of (JGJ/T70.2009 Standard for Test Methods for Basic Properties of Building Mortars.
Chapter 3. Effect of cellulose ether on pure paste and mortar of binary cementitious material of various mineral admixtures
Liquidity Impact
This chapter explores several cellulose ethers and mineral blends by testing a large number of multi-level pure cement-based slurries and mortars and binary cementitious system slurries and mortars with various mineral admixtures and their fluidity and loss over time. The influence law of compound use of materials on the fluidity of clean slurry and mortar, and the influence of various factors are summarized and analyzed.
3.1 Outline of the experimental protocol
In view of the influence of cellulose ether on the working performance of pure cement system and various cementitious material systems, we mainly study in two forms:
1. puree. It has the advantages of intuition, simple operation and high accuracy, and is most suitable for the detection of the adaptability of the admixtures such as cellulose ether to the gelling material, and the contrast is obvious.
2. High fluidity mortar. Achieving a high flow state is also for the convenience of measurement and observation. Here, the adjustment of the reference flow state is mainly controlled by high-performance superplasticizers. In order to reduce the test error, we use a polycarboxylate water reducer with wide adaptability to cement, which is sensitive to temperature, and the test temperature needs to be strictly controlled.
3.2 Influence test of cellulose ether on the fluidity of pure cement paste
3.2.1 Test scheme for the effect of cellulose ether on the fluidity of pure cement paste
Aiming at the influence of cellulose ether on the fluidity of the pure slurry, the pure cement slurry of the one-component cementitious material system was first used to observe the influence. The main reference index here adopts the most intuitive fluidity detection.
The following factors are considered to affect mobility:
1. Types of cellulose ethers
2. Cellulose ether content
3. Slurry rest time
Here, we fixed the PC content of the powder at 0.2%. Three groups and four groups of tests were used for three kinds of cellulose ethers (carboxymethylcellulose sodium CMC, hydroxypropyl methylcellulose HPMC). For sodium carboxymethyl cellulose CMC, the dosage of 0%, O. 10%, O. 2%, namely Og, 0.39, 0.69 (the amount of cement in each test is 3009). , for hydroxypropyl methyl cellulose ether, the dosage is 0%, O. 05%, O. 10%, O. 15%, namely 09, 0.159, 0.39, 0.459.
3.2.2 Test results and analysis of the effect of cellulose ether on the fluidity of pure cement paste
(1) The fluidity test results of pure cement paste mixed with CMC
Analysis of test results:
1. Mobility indicator:
Comparing the three groups with the same standing time, in terms of initial fluidity, with the addition of CMC, the initial fluidity decreased slightly; the half-hour fluidity decreased greatly with the dosage, mainly due to the half-hour fluidity of the blank group. It is 20mm larger than the initial (this may be caused by the retardation of PC powder): -IJ, the fluidity decreases slightly at 0.1% dosage, and increases again at 0.2% dosage .
Comparing the three groups with the same dosage, the fluidity of the blank group was the largest in half an hour, and decreased in one hour (this may be due to the fact that after one hour, the cement particles appeared more hydration and adhesion, the inter-particle structure was initially formed, and the slurry appeared more. Condensation); the fluidity of C1 and C2 groups decreased slightly in half an hour, indicating that the water absorption of CMC had a certain impact on the state; while at the content of C2, there was a large increase in one hour, indicating that the content of The effect of the retardation effect of CMC is dominant.
2. Phenomenon description analysis:
It can be seen that with the increase of the content of CMC, the phenomenon of scratching begins to appear, indicating that CMC has a certain effect on increasing the viscosity of the cement paste, and the air-entraining effect of CMC causes the generation of air bubbles.
(2) The fluidity test results of pure cement paste mixed with HPMC (viscosity 100,000)
Analysis of test results:
1. Mobility indicator:
From the line graph of the effect of standing time on fluidity, it can be seen that the fluidity in half an hour is relatively large compared with the initial and one hour, and with the increase of the content of HPMC, the trend is weakened. Overall, the loss of fluidity is not large, indicating that HPMC has obvious water retention to the slurry, and has a certain retarding effect.
It can be seen from the observation that the fluidity is extremely sensitive to the content of HPMC. In the experimental range, the larger the content of HPMC, the smaller the fluidity. It is basically difficult to fill the fluidity cone mold by itself under the same amount of water. It can be seen that after adding HPMC, the fluidity loss caused by time is not large for the pure slurry.
2. Phenomenon description analysis:
The blank group has bleeding phenomenon, and it can be seen from the sharp change of fluidity with the dosage that HPMC has much stronger water retention and thickening effect than CMC, and plays an important role in eliminating bleeding phenomenon. The large air bubbles should not be understood as the effect of air entrainment. In fact, after the viscosity increases, the air mixed in during the stirring process cannot be beaten into small air bubbles because the slurry is too viscous.
(3) The fluidity test results of pure cement paste mixed with HPMC (viscosity of 150,000)
Analysis of test results:
1. Mobility indicator:
From the line graph of the influence of the content of HPMC (150,000) on the fluidity, the influence of the change of the content on the fluidity is more obvious than that of 100,000 HPMC, indicating that the increase of the viscosity of HPMC will reduce the fluidity.
As far as observation is concerned, according to the overall trend of the change of fluidity with time, the half-hour retarding effect of HPMC (150,000) is obvious, while the effect of -4, is worse than that of HPMC (100,000).
2. Phenomenon description analysis:
There was bleeding in the blank group. The reason for scratching the plate was because the water-cement ratio of the bottom slurry became smaller after bleeding, and the slurry was dense and difficult to scrape from the glass plate. The addition of HPMC played an important role in eliminating the bleeding phenomenon. With the increase of the content, a small amount of small bubbles first appeared and then large bubbles appeared. Small bubbles are mainly caused by a certain cause. Similarly, large bubbles should not be understood as the effect of air entrainment. In fact, after the viscosity increases, the air mixed in during the stirring process is too viscous and cannot overflow from the slurry.
3.3 Influence test of cellulose ether on the fluidity of pure slurry of multi-component cementitious materials
This section mainly explores the effect of the compound use of several admixtures and three cellulose ethers (carboxymethyl cellulose sodium CMC, hydroxypropyl methyl cellulose HPMC) on the fluidity of the pulp.
Similarly, three groups and four groups of tests were used for three kinds of cellulose ethers (carboxymethylcellulose sodium CMC, hydroxypropyl methylcellulose HPMC). For sodium carboxymethyl cellulose CMC, the dosage of 0%, 0.10%, and 0.2%, namely 0g, 0.3g, and 0.6g (the cement dosage for each test is 300g). For hydroxypropyl methylcellulose ether, the dosage is 0%, 0.05%, 0.10%, 0.15%, namely 0g, 0.15g, 0.3g, 0.45g. The PC content of the powder is controlled at 0.2%.
The fly ash and slag powder in the mineral admixture are replaced by the same amount of internal mixing method, and the mixing levels are 10%, 20% and 30%, that is, the replacement amount is 30g, 60g and 90g. However, considering the influence of higher activity, shrinkage, and state, the silica fume content is controlled to 3%, 6%, and 9%, that is, 9g, 18g, and 27g.
3.3.1 Test scheme for the effect of cellulose ether on the fluidity of the pure slurry of the binary cementitious material
(1) Test scheme for the fluidity of binary cementitious materials mixed with CMC and various mineral admixtures.
(2) Test plan for the fluidity of binary cementitious materials mixed with HPMC (viscosity 100,000) and various mineral admixtures.
(3) Test scheme for the fluidity of binary cementitious materials mixed with HPMC (viscosity of 150,000) and various mineral admixtures.
3.3.2 Test results and analysis of the effect of cellulose ether on the fluidity of multi-component cementitious materials
(1) The initial fluidity test results of the binary cementitious material pure slurry mixed with CMC and various mineral admixtures.
It can be seen from this that the addition of fly ash can effectively increase the initial fluidity of the slurry, and it tends to expand with the increase of fly ash content. At the same time, when the content of CMC increases, the fluidity decreases slightly, and the maximum decrease is 20mm.
It can be seen that the initial fluidity of the pure slurry can be increased at low dosage of mineral powder, and the improvement of fluidity is no longer obvious when the dosage is above 20%. At the same time, the amount of CMC in O. At 1%, the fluidity is maximum.
It can be seen from this that the content of silica fume generally has a significant negative effect on the initial fluidity of the slurry. At the same time, CMC also slightly reduced the fluidity.
Half-hour fluidity test results of pure binary cementitious material mixed with CMC and various mineral admixtures.
It can be seen that the improvement of the fluidity of fly ash for half an hour is relatively effective at low dosage, but it may also be because it is close to the flow limit of the pure slurry. At the same time, CMC still has a small reduction in fluidity.
In addition, comparing the initial and half-hour fluidity, it can be found that more fly ash is beneficial to control the loss of fluidity over time.
It can be seen from this that the total amount of mineral powder has no obvious negative effect on the fluidity of the pure slurry for half an hour, and the regularity is not strong. At the same time, the effect of CMC content on the fluidity in half an hour is not obvious, but the improvement of 20% mineral powder replacement group is relatively obvious.
It can be seen that the negative effect of the fluidity of the pure slurry with the amount of silica fume for half an hour is more obvious than the initial one, especially the effect in the range of 6% to 9% is more obvious. At the same time, the decrease of CMC content on the fluidity is about 30mm, which is greater than the decrease of CMC content to the initial.
(2) The initial fluidity test results of the binary cementitious material pure slurry mixed with HPMC (viscosity 100,000) and various mineral admixtures
From this, it can be seen that the effect of fly ash on fluidity is relatively obvious, but it is found in the test that fly ash has no obvious improvement effect on bleeding. In addition, the reducing effect of HPMC on the fluidity is very obvious (especially in the range of 0.1% to 0.15% of high dosage, the maximum decrease can reach more than 50mm).
It can be seen that the mineral powder has little effect on the fluidity, and does not significantly improve the bleeding. In addition, the reducing effect of HPMC on fluidity reaches 60mm in the range of 0.1%～0.15% of high dosage.
From this, it can be seen that the reduction of the fluidity of silica fume is more obvious in the large dosage range, and in addition, the silica fume has obvious improvement effect on bleeding in the test. At the same time, HPMC has an obvious effect on the reduction of fluidity (especially in the range of high dosage (0.1% to 0.15%). In terms of the influencing factors of fluidity, silica fume and HPMC play a key role, and other The admixture acts as an auxiliary small adjustment.
It can be seen that, in general, the effect of the three admixtures on the fluidity is similar to the initial value. When the silica fume is at a high content of 9% and the HPMC content is O. In the case of 15%, the phenomenon that the data could not be collected due to the poor state of the slurry was difficult to fill the cone mold, indicating that the viscosity of silica fume and HPMC increased significantly at higher dosages. Compared with CMC, the viscosity increasing effect of HPMC is very obvious.
(3) The initial fluidity test results of the binary cementitious material pure slurry mixed with HPMC (viscosity 100,000) and various mineral admixtures
From this, it can be seen that HPMC (150,000) and HPMC (100,000) have similar effects on the slurry, but HPMC with high viscosity has a slightly larger decrease in fluidity, but it is not obvious, which should be related to the dissolution of HPMC. The speed has a certain relationship. Among the admixtures, the effect of fly ash content on the fluidity of the slurry is basically linear and positive, and 30% of the content can increase the fluidity by 20,-,30mm; The effect is not obvious, and its improvement effect on bleeding is limited; even at a small dosage level of less than 10%, silica fume has a very obvious effect on reducing bleeding, and its specific surface area is nearly two times larger than that of cement. order of magnitude, the effect of its adsorption of water on the mobility is extremely significant.
In a word, in the respective variation range of the dosage, the factors affecting the fluidity of the slurry, the dosage of silica fume and HPMC is the primary factor, whether it is the control of bleeding or the control of flow state, it is more obvious, other The effect of admixtures is secondary and plays an auxiliary adjustment role.
The third part summarizes the influence of HPMC (150,000) and admixtures on the fluidity of pure pulp in half an hour, which is generally similar to the influence law of the initial value. It can be found that the increase of fly ash on the fluidity of pure slurry for half an hour is slightly more obvious than the increase of initial fluidity, the influence of slag powder is still not obvious, and the influence of silica fume content on fluidity is still very obvious. In addition, in terms of the content of HPMC, there are many phenomena that cannot be poured out at high content, indicating that its O. 15% dosage has a significant effect on increasing viscosity and reducing fluidity, and in terms of fluidity for half an hour, compared with the initial value, the slag group’s O. The fluidity of 05% HPMC decreased obviously.
In terms of the loss of fluidity over time, the incorporation of silica fume has a relatively large impact on it, mainly because silica fume has a large fineness, high activity, fast reaction, and strong ability to absorb moisture, resulting in a relatively sensitive fluidity to standing time. To.
3.4 Experiment on the effect of cellulose ether on the fluidity of pure cement-based high-fluidity mortar
3.4.1 Test scheme for the effect of cellulose ether on the fluidity of pure cement-based high-fluidity mortar
Use high fluidity mortar to observe its effect on workability. The main reference index here is the initial and half-hour mortar fluidity test.
The following factors are considered to affect mobility:
1 types of cellulose ethers,
2 Dosage of cellulose ether,
3 Mortar standing time
3.4.2 Test results and analysis of the effect of cellulose ether on the fluidity of pure cement-based high-fluidity mortar
(1) Fluidity test results of pure cement mortar mixed with CMC
Summary and analysis of test results:
1. Mobility indicator:
Comparing the three groups with the same standing time, in terms of initial fluidity, with the addition of CMC, the initial fluidity decreased slightly, and when the content reached O. At 15%, there is a relatively obvious decrease; the decreasing range of the fluidity with the increase of the content in half an hour is similar to the initial value.
2. Symptom:
Theoretically speaking, compared with clean slurry, the incorporation of aggregates in mortar makes it easier for air bubbles to be entrained into the slurry, and the blocking effect of aggregates on bleeding voids will also make it easier for air bubbles or bleeding to be retained. In the slurry, therefore, the air bubble content and size of the mortar should be more and larger than that of the neat slurry. On the other hand, it can be seen that with the increase of the content of CMC, the fluidity decreases, indicating that CMC has a certain thickening effect on the mortar, and the half-hour fluidity test shows that the bubbles overflowing on the surface slightly increase. , which is also a manifestation of the rising consistency, and when the consistency reaches a certain level, the bubbles will be difficult to overflow, and no obvious bubbles will be seen on the surface.
(2) The fluidity test results of pure cement mortar mixed with HPMC (100,000)
Analysis of test results:
1. Mobility indicator:
It can be seen from the figure that with the increase of the content of HPMC, the fluidity is greatly reduced. Compared with CMC, HPMC has a stronger thickening effect. The effect and water retention are better. From 0.05% to 0.1%, the range of fluidity changes is more obvious, and from O. After 1%, neither the initial nor half-hour change in fluidity is too large.
2. Phenomenon description analysis:
It can be seen from the table and figure that there are basically no bubbles in the two groups of Mh2 and Mh3, indicating that the viscosity of the two groups is already relatively large, preventing the overflow of bubbles in the slurry.
(3) The fluidity test results of pure cement mortar mixed with HPMC (150,000)
Analysis of test results:
1. Mobility indicator:
Comparing several groups with the same standing time, the general trend is that both the initial and half-hour fluidity decrease with the increase of the content of HPMC, and the decrease is more obvious than that of HPMC with a viscosity of 100,000, indicating that the increase of the viscosity of HPMC makes it increase. The thickening effect is strengthened, but in O. The effect of the dosage below 05% is not obvious, the fluidity has a relatively large change in the range of 0.05% to 0.1%, and the trend is again in the range of 0.1% to 0.15%. Slow down, or even stop changing. Comparing the half-hour fluidity loss values (initial fluidity and half-hour fluidity) of HPMC with two viscosities, it can be found that HPMC with high viscosity can reduce the loss value, indicating that its water retention and setting retardation effect is better than that of low viscosity.
2. Phenomenon description analysis:
In terms of controlling bleeding, the two HPMCs have little difference in effect, both of which can effectively retain water and thicken, eliminate the adverse effects of bleeding, and at the same time allow bubbles to overflow effectively.
3.5 Experiment on the effect of cellulose ether on the fluidity of high fluidity mortar of various cementitious material systems
3.5.1 Test scheme for the effect of cellulose ethers on the fluidity of high-fluidity mortars of various cementitious material systems
High fluidity mortar is still used to observe its influence on fluidity. The main reference indicators are the initial and half-hour mortar fluidity detection.
(1) Test scheme of mortar fluidity with binary cementitious materials mixed with CMC and various mineral admixtures
(2) Test scheme of mortar fluidity with HPMC (viscosity 100,000) and binary cementitious materials of various mineral admixtures
(3) Test scheme of mortar fluidity with HPMC (viscosity 150,000) and binary cementitious materials of various mineral admixtures
3.5.2 The effect of cellulose ether on the fluidity of high-fluid mortar in a binary cementitious material system of various mineral admixtures Test results and analysis
(1) Initial fluidity test results of binary cementitious mortar mixed with CMC and various admixtures
From the test results of initial fluidity, it can be concluded that the addition of fly ash can slightly improve the fluidity of mortar; when the content of mineral powder is 10%, the fluidity of mortar can be slightly improved; and silica fume has a greater impact on fluidity , especially in the range of 6%~9% content variation, resulting in a decrease in fluidity of about 90mm.
In the two groups of fly ash and mineral powder, CMC reduces the fluidity of mortar to a certain extent, while in the silica fume group, O. The increase of CMC content above 1% no longer significantly affects the fluidity of mortar.
Half-hour fluidity test results of binary cementitious mortar mixed with CMC and various admixtures
From the test results of the fluidity in half an hour, it can be concluded that the effect of the content of admixture and CMC is similar to the initial one, but the content of CMC in the mineral powder group changes from O. 1% to O. The 2% change is larger, at 30mm.
In terms of the loss of fluidity over time, fly ash has the effect of reducing the loss, while the mineral powder and silica fume will increase the loss value under high dosage. The 9% dosage of silica fume also causes the test mold to not be filled by itself. , the fluidity cannot be accurately measured.
(2) The initial fluidity test results of binary cementitious mortar mixed with HPMC (viscosity 100,000) and various admixtures
Half-hour fluidity test results of binary cementitious mortar mixed with HPMC (viscosity 100,000) and various admixtures
It can still be concluded through experiments that the addition of fly ash can slightly improve the fluidity of mortar; when the content of mineral powder is 10%, the fluidity of mortar can be slightly improved; The dosage is very sensitive, and the HPMC group with high dosage at 9% has dead spots, and the fluidity basically disappears.
The content of cellulose ether and silica fume are also the most obvious factors affecting the fluidity of mortar. The effect of HPMC is obviously greater than that of CMC. Other admixtures can improve the loss of fluidity over time.
(3) The initial fluidity test results of binary cementitious mortar mixed with HPMC (viscosity of 150,000) and various admixtures
Half-hour fluidity test results of binary cementitious mortar mixed with HPMC (viscosity 150,000) and various admixtures
It can still be concluded through experiments that the addition of fly ash can slightly improve the fluidity of mortar; when the content of mineral powder is 10%, the fluidity of mortar can be slightly improved: silica fume is still very effective in solving the bleeding phenomenon, while the Fluidity is a serious side effect, but is less effective than its effect in clean slurries.
A large number of dead spots appeared under the high content of cellulose ether (especially in the table of half-hour fluidity), indicating that HPMC has a significant effect on reducing the fluidity of mortar, and mineral powder and fly ash can improve the loss of fluidity over time.
3.5 Chapter Summary
1. Comprehensively comparing the fluidity test of pure cement paste mixed with three cellulose ethers, it can be seen that
1. CMC has certain retarding and air-entraining effects, weak water retention, and certain loss over time.
2. The water retention effect of HPMC is obvious, and it has a significant influence on the state, and the fluidity decreases significantly with the increase of the content. It has a certain air-entraining effect, and the thickening is obvious. 15% will cause large bubbles in the slurry, which is bound to be detrimental to the strength. With the increase of HPMC viscosity, the time-dependent loss of slurry fluidity slightly increased, but not obvious.
2. Comprehensively comparing the slurry fluidity test of the binary gelling system of various mineral admixtures mixed with three cellulose ethers, it can be seen that:
1. The influence law of the three cellulose ethers on the fluidity of the slurry of the binary cementitious system of various mineral admixtures has the characteristics similar to the influence law of the fluidity of the pure cement slurry. CMC has little effect on controlling bleeding, and has a weak effect on reducing fluidity; two kinds of HPMC can increase the viscosity of slurry and reduce fluidity significantly, and the one with higher viscosity has a more obvious effect.
2. Among the admixtures, fly ash has a certain degree of improvement on the initial and half-hour fluidity of the pure slurry, and the content of 30% can be increased by about 30mm; the effect of mineral powder on the fluidity of the pure slurry has no obvious regularity; silicon Although the content of ash is low, its unique ultra-fineness, fast reaction, and strong adsorption make it significantly reduce the fluidity of the slurry, especially when 0.15% HPMC is added, there will be cone molds that cannot be filled. The phenomenon.
3. In the control of bleeding, fly ash and mineral powder are not obvious, and silica fume can obviously reduce the amount of bleeding.
4. In terms of the half-hour loss of fluidity, the loss value of fly ash is smaller, and the loss value of the group incorporating silica fume is larger.
5. In the respective variation range of the content, the factors affecting the fluidity of the slurry, the content of HPMC and silica fume are the primary factors, whether it is the control of the bleeding or the control of the flow state, it is relatively obvious. The influence of mineral powder and mineral powder is secondary, and plays an auxiliary adjustment role.
3. Comprehensively comparing the fluidity test of pure cement mortar mixed with three cellulose ethers, it can be seen that
1. After adding the three cellulose ethers, the bleeding phenomenon was effectively eliminated, and the fluidity of the mortar generally decreased. Certain thickening, water retention effect. CMC has certain retarding and air-entraining effects, weak water retention, and certain loss over time.
2. After adding CMC, the loss of mortar fluidity over time increases, which may be because CMC is an ionic cellulose ether, which is easy to form precipitation with Ca2+ in cement.
3. The comparison of the three cellulose ethers shows that CMC has little effect on the fluidity, and the two kinds of HPMC significantly reduce the fluidity of the mortar at the content of 1/1000, and the one with the higher viscosity is slightly more obvious.
4. The three kinds of cellulose ethers have certain air-entraining effect, which will cause the surface bubbles to overflow, but when the content of HPMC reaches more than 0.1%, due to the high viscosity of the slurry, the bubbles remain in the slurry and cannot overflow.
5. The water retention effect of HPMC is obvious, which has a significant impact on the state of the mixture, and the fluidity decreases significantly with the increase of the content, and the thickening is obvious.
4. Comprehensively compare the fluidity test of multiple mineral admixture binary cementitious materials mixed with three cellulose ethers.
As can be seen:
1. The influence law of three cellulose ethers on the fluidity of multi-component cementitious material mortar is similar to the influence law on the fluidity of pure slurry. CMC has little effect on controlling bleeding, and has a weak effect on reducing fluidity; two kinds of HPMC can increase the viscosity of mortar and reduce fluidity significantly, and the one with higher viscosity has a more obvious effect.
2. Among the admixtures, fly ash has a certain degree of improvement on the initial and half-hour fluidity of the clean slurry; the influence of slag powder on the fluidity of the clean slurry has no obvious regularity; although the content of silica fume is low, its The unique ultra-fineness, fast reaction and strong adsorption make it have a great reduction effect on the fluidity of the slurry. However, compared with the test results of pure paste, it is found that the effect of admixtures tends to weaken.
3. In the control of bleeding, fly ash and mineral powder are not obvious, and silica fume can obviously reduce the amount of bleeding.
4. In the respective variation range of the dosage, the factors affecting the fluidity of the mortar, the dosage of HPMC and silica fume are the primary factors, whether it is the control of bleeding or the control of the flow state, it is more obvious, the silica fume 9% When the content of HPMC is 0.15%, it is easy to cause the filling mold to be difficult to fill, and the influence of other admixtures is secondary and plays an auxiliary adjustment role.
5. There will be bubbles on the surface of the mortar with a fluidity of more than 250mm, but the blank group without cellulose ether generally has no bubbles or only a very small amount of bubbles, indicating that cellulose ether has a certain air-entraining effect and makes the slurry viscous. In addition, due to the excessive viscosity of the mortar with poor fluidity, it is difficult for the air bubbles to float up by the self-weight effect of the slurry, but is retained in the mortar, and its influence on the strength cannot be ignored.
Chapter 4 Effects of Cellulose Ethers on Mechanical Properties of Mortar
The previous chapter studied the effect of the combined use of cellulose ether and various mineral admixtures on the fluidity of the clean slurry and high fluidity mortar. This chapter mainly analyzes the combined use of cellulose ether and various admixtures on the high fluidity mortar And the influence of the compressive and flexural strength of the bonding mortar, and the relationship between the tensile bonding strength of the bonding mortar and the cellulose ether and mineral admixtures is also summarized and analyzed.
According to the research on the working performance of cellulose ether to cement-based material of pure paste and mortar in Chapter 3, in the aspect of strength test, the content of cellulose ether is 0.1%.
4.1 Compressive and flexural strength test of high fluidity mortar
The compressive and flexural strengths of mineral admixtures and cellulose ethers in high-fluidity infusion mortar were investigated.
4.1.1 Influence test on compressive and flexural strength of pure cement-based high fluidity mortar
The effect of three kinds of cellulose ethers on the compressive and flexural properties of pure cement-based high-fluid mortar at various ages at a fixed content of 0.1% was conducted here.
Early strength analysis: In terms of flexural strength, CMC has a certain strengthening effect, while HPMC has a certain reducing effect; in terms of compressive strength, the incorporation of cellulose ether has a similar law with the flexural strength; the viscosity of HPMC affects the two strengths. It has little effect: in terms of the pressure-fold ratio, all three cellulose ethers can effectively reduce the pressure-fold ratio and enhance the flexibility of the mortar. Among them, HPMC with a viscosity of 150,000 has the most obvious effect.
(2) Seven-day strength comparison test results
Seven-day strength analysis: In terms of flexural strength and compressive strength, there is a similar law to the three-day strength. Compared with the three-day pressure-folding, there is a slight increase in the pressure-folding strength. However, the comparison of the data of the same age period can see the effect of HPMC on the reduction of the pressure-folding ratio. relatively obvious.
(3) Twenty-eight days strength comparison test results
Twenty-eight-day strength analysis: In terms of flexural strength and compressive strength, there are similar laws to the three-day strength. The flexural strength increases slowly, and the compressive strength still increases to a certain extent. The data comparison of the same age period shows that HPMC has a more obvious effect on improving the compression-folding ratio.
According to the strength test of this section, it is found that the improvement of the brittleness of the mortar is limited by CMC, and sometimes the compression-to-fold ratio is increased, making the mortar more brittle. At the same time, since the water retention effect is more general than that of HPMC, the cellulose ether we consider for the strength test here is HPMC of two viscosities. Although HPMC has a certain effect on reducing the strength (especially for the early strength), it is beneficial to reduce the compression-refraction ratio, which is beneficial to the toughness of the mortar. In addition, combined with the factors affecting the fluidity in Chapter 3, in the study of the compounding of admixtures and CE In the test of the effect, we will use HPMC (100,000) as the matching CE.
4.1.2 Influence test of compressive and flexural strength of mineral admixture high fluidity mortar
According to the test of the fluidity of pure slurry and mortar mixed with admixtures in the previous chapter, it can be seen that the fluidity of silica fume is obviously deteriorated due to the large water demand, although it can theoretically improve the density and strength to a certain extent. , especially the compressive strength, but it is easy to cause the compression-to-fold ratio to be too large, which makes the mortar brittleness feature remarkable, and it is a consensus that silica fume increases the shrinkage of the mortar. At the same time, due to the lack of skeleton shrinkage of coarse aggregate, the shrinkage value of mortar is relatively large relative to concrete. For mortar (especially special mortar such as bonding mortar and plastering mortar), the biggest harm is often shrinkage. For cracks caused by water loss, strength is often not the most critical factor. Therefore, silica fume was discarded as the admixture, and only fly ash and mineral powder were used to explore the effect of its composite effect with cellulose ether on the strength.
4.1.2.1 Compressive and flexural strength test scheme of high fluidity mortar
In this experiment, the proportion of mortar in 4.1.1 was used, and the content of cellulose ether was fixed at 0.1% and compared with the blank group. The dosage level of the admixture test is 0%, 10%, 20% and 30%.
4.1.2.2 Compressive and flexural strength test results and analysis of high fluidity mortar
It can be seen from the compressive strength test value that the 3d compressive strength after adding HPMC is about 5/VIPa lower than that of the blank group. In general, with the increase of the amount of admixture added, the compressive strength shows a decreasing trend. . In terms of admixtures, the strength of the mineral powder group without HPMC is the best, while the strength of the fly ash group is slightly lower than that of the mineral powder group, indicating that the mineral powder is not as active as the cement, and its incorporation will slightly reduce the early strength of the system. The fly ash with poorer activity reduces the strength more obviously. The reason for the analysis should be that the fly ash mainly participates in the secondary hydration of cement, and does not contribute significantly to the early strength of the mortar.
It can be seen from the flexural strength test values that HPMC still has an adverse effect on the flexural strength, but when the content of the admixture is higher, the phenomenon of reducing the flexural strength is no longer obvious. The reason may be the water retention effect of HPMC. The water loss rate on the surface of the mortar test block is slowed down, and the water for hydration is relatively sufficient.
In terms of admixtures, the flexural strength shows a decreasing trend with the increase of the admixture content, and the flexural strength of the mineral powder group is also slightly larger than that of the fly ash group, indicating that the activity of the mineral powder is greater than that of the fly ash.
It can be seen from the calculated value of the compression-reduction ratio that the addition of HPMC will effectively lower the compression ratio and improve the flexibility of the mortar, but it is actually at the expense of a substantial reduction in the compressive strength.
In terms of admixtures, as the amount of admixture increases, the compression-fold ratio tends to increase, indicating that the admixture is not conducive to the flexibility of the mortar. In addition, it can be found that the compression-fold ratio of the mortar without HPMC increases with the addition of the admixture. The increase is slightly larger, that is, HPMC can improve the embrittlement of mortar caused by the addition of admixtures to a certain extent.
It can be seen that for the compressive strength of 7d, the adverse effects of the admixtures are no longer obvious. The compressive strength values are roughly the same at each admixture dosage level, and HPMC still has a relatively obvious disadvantage on the compressive strength. effect.
It can be seen that in terms of flexural strength, the admixture has an adverse effect on the 7d flexural resistance as a whole, and only the group of mineral powders performed better, basically maintained at 11-12MPa.
It can be seen that the admixture has an adverse effect in terms of the indentation ratio. With the increase of the amount of the admixture, the indentation ratio gradually increases, that is, the mortar is brittle. HPMC can obviously reduce the compression-fold ratio and improve the brittleness of mortar.
It can be seen that from the 28d compressive strength, the admixture has played a more obvious beneficial effect on the later strength, and the compressive strength has been increased by 3-5MPa, which is mainly due to the micro-filling effect of the admixture and the pozzolanic substance. The secondary hydration effect of the material, on the one hand, can utilize and consume the calcium hydroxide produced by cement hydration (calcium hydroxide is a weak phase in the mortar, and its enrichment in the interface transition zone is detrimental to the strength), generating more More hydration products, on the other hand, promote the hydration degree of cement and make the mortar more dense. HPMC still has a significant adverse effect on the compressive strength, and the weakening strength can reach more than 10MPa. To analyze the reasons, HPMC introduces a certain amount of air bubbles in the mortar mixing process, which reduces the compactness of the mortar body. This is one reason. HPMC is easily adsorbed on the surface of solid particles to form a film, hindering the hydration process, and the interface transition zone is weaker, which is not conducive to strength.
It can be seen that in terms of 28d flexural strength, the data has a larger dispersion than compressive strength, but the adverse effect of HPMC can still be seen.
It can be seen that, from the point of view of the compression-reduction ratio, HPMC is generally beneficial to reduce the compression-reduction ratio and improve the toughness of the mortar. In one group, with the increase of the amount of admixtures, the compression-refraction ratio increases. Analysis of the reasons shows that the admixture has obvious improvement in the later compressive strength, but limited improvement in the later flexural strength, resulting in the compression-refraction ratio. improvement.
4.2 Compressive and flexural strength tests of bonded mortar
In order to explore the influence of cellulose ether and admixture on the compressive and flexural strength of bonded mortar, the experiment fixed the content of cellulose ether HPMC (viscosity 100,000) as 0.30% of the dry weight of the mortar. and compared with the blank group.
Admixtures (fly ash and slag powder) are still tested at 0%, 10%, 20%, and 30%.
4.2.1 Compressive and flexural strength test scheme of bonded mortar
4.2.2 Test results and analysis of the influence of compressive and flexural strength of bonded mortar
It can be seen from the experiment that HPMC is obviously unfavorable in terms of the 28d compressive strength of the bonding mortar, which will cause the strength to decrease by about 5MPa, but the key indicator for judging the quality of the bonding mortar is not the compressive strength, so it is acceptable; When the compound content is 20%, the compressive strength is relatively ideal.
It can be seen from the experiment that from the perspective of flexural strength, the strength reduction caused by HPMC is not large. It may be that the bonding mortar has poor fluidity and obvious plastic characteristics compared with high-fluid mortar. The positive effects of slipperiness and water retention effectively offset some of the negative effects of introducing gas to reduce compactness and interface weakening; admixtures have no obvious effect on flexural strength, and the data of fly ash group fluctuates slightly.
It can be seen from the experiments that, as far as the pressure-reduction ratio is concerned, in general, the increase of the admixture content increases the pressure-reduction ratio, which is unfavorable to the toughness of the mortar; HPMC has a favorable effect, which can reduce the pressure-reduction ratio by O. 5 above, it should be pointed out that, according to “JG 149.2003 Expanded Polystyrene Board Thin Plaster External Wall External Insulation System”, there is generally no mandatory requirement for the compression-folding ratio in the detection index of the bonding mortar, and the compression-folding ratio is mainly It is used to limit the brittleness of the plastering mortar, and this index is only used as a reference for the flexibility of the bonding mortar.
4.3 Bonding Strength Test of Bonding Mortar
In order to explore the influence law of the composite application of cellulose ether and admixture on the bond strength of bonded mortar, refer to “JG/T3049.1998 Putty for Building Interior” and “JG 149.2003 Expanded Polystyrene Board Thin Plastering Exterior Walls” Insulation System”, we carried out the bond strength test of the bonding mortar, using the bonding mortar ratio in Table 4.2.1, and fixing the content of cellulose ether HPMC (viscosity 100,000) to 0 of the dry weight of the mortar .30%, and compared with the blank group.
Admixtures (fly ash and slag powder) are still tested at 0%, 10%, 20%, and 30%.
4.3.1 Test scheme of bond strength of bond mortar
4.3.2 Test results and analysis of bond strength of bond mortar
(1) 14d bond strength test results of bonding mortar and cement mortar
It can be seen from the experiment that the groups added with HPMC are significantly better than the blank group, indicating that HPMC is beneficial to the bonding strength, mainly because the water retention effect of HPMC protects the water at the bonding interface between the mortar and the cement mortar test block. The bonding mortar at the interface is fully hydrated, thereby increasing the bond strength.
In terms of admixtures, the bond strength is relatively high at a dosage of 10%, and although the hydration degree and speed of the cement can be improved at a high dosage, it will lead to a decrease in the overall hydration degree of the cementitious material, thus causing stickiness. decrease in knot strength.
It can be seen from the experiment that in terms of the test value of the operational time intensity, the data is relatively discrete, and the admixture has little effect, but in general, compared with the original intensity, there is a certain decrease, and the decrease of HPMC is smaller than that of the blank group, indicating that It is concluded that the water retention effect of HPMC is beneficial to the reduction of water dispersion, so that the decrease of mortar bond strength decreases after 2.5h.
(2) 14d bond strength test results of bonding mortar and expanded polystyrene board
It can be seen from the experiment that the test value of the bond strength between the bonding mortar and the polystyrene board is more discrete. In general, it can be seen that the group mixed with HPMC is more effective than the blank group due to better water retention. Well, the incorporation of admixtures reduces the stability of the bond strength test.
4.4 Chapter Summary
1. For high fluidity mortar, with the increase of age, the compressive-fold ratio has an upward trend; the incorporation of HPMC has an obvious effect of reducing the strength (the decrease in the compressive strength is more obvious), which also leads to The decrease of the compression-folding ratio, that is, HPMC has obvious help to the improvement of mortar toughness. In terms of three-day strength, fly ash and mineral powder can make a slight contribution to the strength at 10%, while the strength decreases at high dosage, and the crushing ratio increases with the increase of mineral admixtures; in the seven-day strength, The two admixtures have little effect on the strength, but the overall effect of fly ash strength reduction is still obvious; in terms of the 28-day strength, the two admixtures have contributed to the strength, compressive and flexural strength. Both were slightly increased, but the pressure-fold ratio still increased with the increase of the content.
2. For the 28d compressive and flexural strength of the bonded mortar, when the admixture content is 20%, the compressive and flexural strength performance is better, and the admixture still leads to a small increase in the compressive-fold ratio, reflecting its Adverse effect on the toughness of mortar; HPMC leads to a significant decrease in strength, but can significantly reduce the compression-to-fold ratio.
3. Regarding the bond strength of the bonded mortar, HPMC has a certain favorable influence on the bond strength. The analysis should be that its water retention effect reduces the loss of mortar moisture and ensures more sufficient hydration; The relationship between the content of the mixture is not regular, and the overall performance is better with cement mortar when the content is 10%.
Chapter 5 A Method for Predicting the Compressive Strength of Mortar and Concrete
In this chapter, a method for predicting the strength of cement-based materials based on admixture activity coefficient and FERET strength theory is proposed. We first think of mortar as a special kind of concrete without coarse aggregates.
It is well known that compressive strength is an important indicator for cement-based materials (concrete and mortar) used as structural materials. However, due to many influencing factors, there is no mathematical model that can accurately predict its intensity. This causes certain inconvenience to the design, production and use of mortar and concrete. The existing models of concrete strength have their own advantages and disadvantages: some predict the strength of concrete through the porosity of concrete from the common point of view of the porosity of solid materials; some focus on the influence of the water-binder ratio relationship on the strength. This paper mainly combines the activity coefficient of pozzolanic admixture with Feret’s strength theory, and makes some improvements to make it relatively more accurate to predict the compressive strength.
5.1 Feret’s Strength Theory
In 1892, Feret established the earliest mathematical model for predicting compressive strength. Under the premise of given concrete raw materials, the formula for predicting concrete strength is proposed for the first time.
The advantage of this formula is that the grout concentration, which correlates with concrete strength, has a well-defined physical meaning. At the same time, the influence of air content is taken into account, and the correctness of the formula can be proved physically. The rationale for this formula is that it expresses information that there is a limit to the concrete strength that can be obtained. The disadvantage is that it ignores the influence of aggregate particle size, particle shape and aggregate type. When predicting the strength of concrete at different ages by adjusting the K value, the relationship between different strength and age is expressed as a set of divergences through the coordinate origin. The curve is inconsistent with the actual situation (especially when the age is longer). Of course, this formula proposed by Feret is designed for the mortar of 10.20MPa. It cannot fully adapt to the improvement of concrete compressive strength and the influence of increasing components due to the progress of mortar concrete technology.
It is considered here that the strength of concrete (especially for ordinary concrete) mainly depends on the strength of the cement mortar in the concrete, and the strength of the cement mortar depends on the density of the cement paste, that is, the volume percentage of the cementitious material in the paste.
The theory is closely related to the effect of void ratio factor on strength. However, because the theory was put forward earlier, the influence of admixture components on concrete strength was not considered. In view of this, this paper will introduce the admixture influence coefficient based on the activity coefficient for partial correction. At the same time, on the basis of this formula, an influence coefficient of porosity on concrete strength is reconstructed.
5.2 Activity coefficient
The activity coefficient, Kp, is used to describe the effect of pozzolanic materials on the compressive strength. Obviously, it depends on the nature of the pozzolanic material itself, but also on the age of the concrete. The principle of determining the activity coefficient is to compare the compressive strength of a standard mortar with the compressive strength of another mortar with pozzolanic admixtures and replacing the cement with the same amount of cement quality (the country p is the activity coefficient test. Use surrogate percentages). The ratio of these two intensities is called the activity coefficient fO), where t is the age of the mortar at the time of testing. If fO) is less than 1, the activity of pozzolan is less than that of cement r. Conversely, if fO) is greater than 1, the pozzolan has a higher reactivity (this usually happens when silica fume is added).
For the commonly used activity coefficient at 28-day compressive strength, according to ((GBT18046.2008 Granulated blast furnace slag powder used in cement and concrete) H90, the activity coefficient of granulated blast furnace slag powder is in standard cement mortar The strength ratio obtained by replacing 50% cement on the basis of the test; according to ((GBT1596.2005 Fly ash used in cement and concrete), the activity coefficient of fly ash is obtained after replacing 30% cement on the basis of the standard cement mortar test According to “GB.T27690.2011 Silica Fume for Mortar and Concrete”, the activity coefficient of silica fume is the strength ratio obtained by replacing 10% cement on the basis of standard cement mortar test.
Generally, granulated blast furnace slag powder Kp=0.95～1.10, fly ash Kp=0.7-1.05, silica fume Kp=1.00～1.15. We assume that its effect on strength is independent of cement. That is, the mechanism of the pozzolanic reaction should be controlled by the reactivity of the pozzolan, not by the lime precipitation rate of cement hydration.
5.3 Influence coefficient of admixture on strength
5.4 Influence coefficient of water consumption on strength
5.5 Influence coefficient of aggregate composition on strength
According to the views of professors P K Mehta and P C Aitcin in the United States, in order to achieve the best workability and strength properties of HPC at the same time, the volume ratio of cement slurry to aggregate should be 35:65 [4810] Because of the general plasticity and fluidity The total amount of aggregate of concrete does not change much. As long as the strength of the aggregate base material itself meets the requirements of the specification, the influence of the total amount of aggregate on the strength is ignored, and the overall integral fraction can be determined within 60-70% according to the slump requirements.
It is theoretically believed that the ratio of coarse and fine aggregates will have a certain influence on the strength of concrete. As we all know, the weakest part in concrete is the interface transition zone between aggregate and cement and other cementitious material pastes. Therefore, the final failure of common concrete is due to the initial damage of the interface transition zone under stress caused by factors such as load or temperature change. caused by the continuous development of cracks. Therefore, when the degree of hydration is similar, the larger the interface transition zone is, the easier the initial crack will develop into a long through crack after stress concentration. That is to say, the more coarse aggregates with more regular geometric shapes and larger scales in the interface transition zone, the greater the stress concentration probability of the initial cracks, and the macroscopically manifested that the concrete strength increases with the increase of the coarse aggregate ratio. reduced. However, the above premise is that it is required to be medium sand with very little mud content.
The sand rate also has a certain influence on the slump. Therefore, the sand rate can be preset by the slump requirements, and can be determined within 32% to 46% for ordinary concrete.
The amount and variety of admixtures and mineral admixtures are determined by trial mix. In ordinary concrete, the amount of mineral admixture should be less than 40%, while in high-strength concrete, silica fume should not exceed 10%. The amount of cement should not be greater than 500kg/m3.
5.6 Application of this prediction method to guide mix proportion calculation example
The materials used are as follows:
The cement is E042.5 cement produced by Lubi Cement Factory, Laiwu City, Shandong Province, and its density is 3.19/cm3;
The fly ash is grade II ball ash produced by Jinan Huangtai Power Plant, and its activity coefficient is O. 828, its density is 2.59/cm3;
The silica fume produced by Shandong Sanmei Silicon Material Co., Ltd. has an activity coefficient of 1.10 and a density of 2.59/cm3;
Taian dry river sand has a density of 2.6 g/cm3, a bulk density of 1480kg/m3, and a fineness modulus of Mx=2.8;
Jinan Ganggou produces 5-’25mm dry crushed stone with a bulk density of 1500kg/m3 and a density of about 2.7∥cm3;
The water-reducing agent used is a self-made aliphatic high-efficiency water-reducing agent, with a water-reducing rate of 20%; the specific dosage is determined experimentally according to the requirements of slump. Trial preparation of C30 concrete, the slump is required to be greater than 90mm.
1. formulation strength
2. sand quality
3. Determination of Influence Factors of Each Intensity
4. Ask for water consumption
5. The dosage of water-reducing agent is adjusted according to the requirement of slump. The dosage is 1%, and Ma=4kg is added to the mass.
6. In this way, the calculation ratio is obtained
7. After trial mixing, it can meet the slump requirements. The measured 28d compressive strength is 39.32MPa, which meets the requirements.
5.7 Chapter Summary
In the case of ignoring the interaction of the admixtures I and F, we have discussed the activity coefficient and Feret’s strength theory, and obtained the influence of multiple factors on the strength of concrete:
1 Concrete admixture influence coefficient
2 Influence coefficient of water consumption
3 Influence coefficient of aggregate composition
4 Actual comparison. It is verified that the 28d strength prediction method of concrete improved by the activity coefficient and Feret’s strength theory is in good agreement with the actual situation, and it can be used to guide the preparation of mortar and concrete.
Chapter 6 Conclusion and Outlook
6.1 Main conclusions
The first part comprehensively compares the clean slurry and mortar fluidity test of various mineral admixtures mixed with three kinds of cellulose ethers, and finds the following main rules:
1. Cellulose ether has certain retarding and air-entraining effects. Among them, CMC has a weak water retention effect at low dosage, and has a certain loss over time; while HPMC has a significant water retention and thickening effect, which significantly reduces the fluidity of pure pulp and mortar, and The thickening effect of HPMC with high nominal viscosity is slightly obvious.
2. Among the admixtures, the initial and half-hour fluidity of fly ash on the clean slurry and mortar has been improved to a certain extent. The 30% content of the clean slurry test can be increased by about 30mm; the fluidity of the mineral powder on the clean slurry and mortar There is no obvious rule of influence; although the content of silica fume is low, its unique ultra-fineness, fast reaction, and strong adsorption make it have a significant reduction effect on the fluidity of clean slurry and mortar, especially when mixed with 0.15 When %HPMC, there will be a phenomenon that the cone die cannot be filled. Compared with the test results of the clean slurry, it is found that the effect of the admixture in the mortar test tends to weaken. In terms of controlling bleeding, fly ash and mineral powder are not obvious. Silica fume can significantly reduce the amount of bleeding, but it is not conducive to the reduction of mortar fluidity and loss over time, and it is easy to reduce the operating time.
3. In the respective range of dosage changes, the factors affecting the fluidity of cement-based slurry, the dosage of HPMC and silica fume are the primary factors, both in the control of bleeding and the control of flow state, are relatively obvious. The influence of coal ash and mineral powder is secondary and plays an auxiliary adjustment role.
4. The three kinds of cellulose ethers have a certain air-entraining effect, which will cause bubbles to overflow on the surface of the pure slurry. However, when the content of HPMC reaches more than 0.1%, due to the high viscosity of the slurry, the bubbles cannot be retained in the slurry. overflow. There will be bubbles on the surface of mortar with a fluidity above 250ram, but the blank group without cellulose ether generally has no bubbles or only a very small amount of bubbles, indicating that cellulose ether has a certain air-entraining effect and makes the slurry viscous. In addition, due to the excessive viscosity of the mortar with poor fluidity, it is difficult for the air bubbles to float up by the self-weight effect of the slurry, but is retained in the mortar, and its influence on the strength cannot be ignored.
Part II Mortar Mechanical Properties
1. For high fluidity mortar, with the increase of age, the crushing ratio has an upward trend; the addition of HPMC has a significant effect of reducing the strength (the decrease in the compressive strength is more obvious), which also leads to the crushing The decrease of the ratio, that is, HPMC has obvious help to the improvement of mortar toughness. In terms of three-day strength, fly ash and mineral powder can make a slight contribution to the strength at 10%, while the strength decreases at high dosage, and the crushing ratio increases with the increase of mineral admixtures; in the seven-day strength, The two admixtures have little effect on the strength, but the overall effect of fly ash strength reduction is still obvious; in terms of the 28-day strength, the two admixtures have contributed to the strength, compressive and flexural strength. Both were slightly increased, but the pressure-fold ratio still increased with the increase of the content.
2. For the 28d compressive and flexural strength of the bonded mortar, when the admixture content is 20%, the compressive and flexural strengths are better, and the admixture still leads to a small increase in the compressive-to-fold ratio, reflecting its effect on the mortar. Adverse effects of toughness; HPMC leads to a significant decrease in strength.
3. Regarding the bond strength of bonded mortar, HPMC has a certain favorable effect on the bond strength. The analysis should be that its water retention effect reduces the loss of water in the mortar and ensures more sufficient hydration. The bond strength is related to the admixture. The relationship between the dosage is not regular, and the overall performance is better with cement mortar when the dosage is 10%.
4. CMC is not suitable for cement-based cementitious materials, its water retention effect is not obvious, and at the same time, it makes the mortar more brittle; while HPMC can effectively reduce the compression-to-fold ratio and improve the toughness of mortar, but it is at the expense of a substantial reduction in compressive strength.
5. Comprehensive fluidity and strength requirements, HPMC content of 0.1% is more appropriate. When fly ash is used for structural or reinforced mortar that requires fast hardening and early strength, the dosage should not be too high, and the maximum dosage is about 10%. Requirements; considering factors such as the poor volume stability of mineral powder and silica fume, they should be controlled at 10% and n 3% respectively. The effects of admixtures and cellulose ethers are not significantly correlated, with
have an independent effect.
The third part In the case of ignoring the interaction between admixtures, through the discussion of the activity coefficient of mineral admixtures and Feret’s strength theory, the influence law of multiple factors on the strength of concrete (mortar) is obtained:
1. Mineral Admixture Influence Coefficient
2. Influence coefficient of water consumption
3. Influence factor of aggregate composition
4. The actual comparison shows that the 28d strength prediction method of concrete improved by the activity coefficient and Feret strength theory is in good agreement with the actual situation, and it can be used to guide the preparation of mortar and concrete.
6.2 Deficiencies and Prospects
This paper mainly studies the fluidity and mechanical properties of the clean paste and mortar of the binary cementitious system. The effect and influence of the joint action of multi-component cementitious materials need to be further studied. In the test method, mortar consistency and stratification can be used. The effect of cellulose ether on the consistency and water retention of mortar is studied by the degree of cellulose ether. In addition, the microstructure of mortar under the compound action of cellulose ether and mineral admixture is also to be studied.
Cellulose ether is now one of the indispensable admixture components of various mortars. Its good water retention effect prolongs the operating time of the mortar, makes the mortar have good thixotropy, and improves the toughness of the mortar. It is convenient for construction; and the application of fly ash and mineral powder as an industrial waste in mortar can also create great economic and environmental benefits
Post time: Sep-29-2022