Cellulose ether on the slag sand mortar

Using P·II 52.5 grade cement as the cementitious material and steel slag sand as fine aggregate, the steel slag sand with high fluidity and high strength is prepared by adding chemical additives such as water reducer, latex powder and defoamer Special mortar, and the effects of two different viscosities (2000mPa·s and 6000mPa·s) of hydroxypropyl methylcellulose ether (HPMC) on its water retention, fluidity and strength were studied. The results show that: (1) Both HPMC2000 and HPMC6000 can significantly increase the water retention rate of freshly mixed mortar and improve its water retention performance; (2) When the content of cellulose ether is low, the effect on the fluidity of the mortar is not obvious. When it is increased to 0.25% or above, it has a certain deterioration effect on the fluidity of the mortar, among which the deterioration effect of HPMC6000 is more obvious; (3) the addition of cellulose ether has no obvious effect on the 28-day compressive strength of the mortar, but the addition of HPMC2000 Improper time, it is obviously unfavorable to the flexural strength of different ages, and at the same time significantly reduces the early (3 days and 7 days) compressive strength of mortar; (4) The addition of HPMC6000 has a certain effect on the flexural strength of different ages , but the reduction was significantly lower than that of HPMC2000. In this paper, it is considered that HPMC6000 should be selected when preparing steel slag sand special mortar with high fluidity, high water retention rate and high strength, and the dosage should not be greater than 0.20%.

Key words: steel slag sand; cellulose ether; viscosity; working performance; strength

introduction

Steel slag is a by-product of the production of steel. With the development of the iron and steel industry, the annual discharge of steel slag has increased by about 100 million tons in recent years, and the problem of stockpiling due to the failure of timely resource utilization is very serious. Therefore, resource utilization and disposal of steel slag through scientific and effective methods is a problem that cannot be ignored. Steel slag has the characteristics of high density, hard texture and high compressive strength, and can be used as a substitute for natural sand in cement mortar or concrete. Steel slag also has a certain reactivity. Steel slag is ground into a certain fineness powder (steel slag powder). After being mixed into concrete, it can exert a pozzolanic effect, which helps to enhance the strength of the slurry and improve the interface transition between concrete aggregate and slurry. area, thereby increasing the strength of the concrete. However, it must be paid attention to that the steel slag discharged without any measures, its internal free calcium oxide, free magnesium oxide and RO phase will cause poor volume stability of the steel slag, which largely limits the use of steel slag as coarse and fine aggregates. Application in cement mortar or concrete. Wang Yuji et al. summarized different steel slag treatment processes and found that the steel slag treated by hot stuffing method has good stability and can eliminate its expansion problem in cement concrete, and the hot stuffy treatment process was actually implemented in Shanghai No. 3 Iron and Steel Plant for the first time. In addition to the problem of stability, steel slag aggregates also have the characteristics of rough pores, multi-angles, and a small amount of hydration products on the surface. When used as aggregates to prepare mortar and concrete, their working performance is often affected. At present, under the premise of ensuring volume stability, using steel slag as fine aggregate to prepare special mortar is an important direction for resource utilization of steel slag. The study found that adding water reducer, latex powder, cellulose ether, air-entraining agent and defoamer to the steel slag sand mortar can improve the mixture performance and hardened performance of the steel slag sand mortar as required . The author has used the measures of adding latex powder and other admixtures to prepare steel slag sand high-strength repair mortar. In the production and application of mortar, cellulose ether is the most common chemical admixture. The most commonly used cellulose ethers in mortar are hydroxypropyl methyl cellulose ether (HPMC) and hydroxyethyl methyl cellulose ether (HEMC). )Wait. Cellulose ether can improve the working performance of mortar to a large extent, such as giving mortar excellent water retention through thickening, but adding cellulose ether will also affect the fluidity, air content, setting time and hardening of mortar. Various properties.

In order to better guide the development and application of steel slag sand mortar, on the basis of the previous research work on steel slag sand mortar, this paper uses two kinds of viscosities (2000mPa·s and 6000mPa·s) of hydroxypropyl methyl cellulose ether (HPMC) Carry out experimental research on the influence of steel slag sand high-strength mortar on working performance (fluidity and water retention) and compressive and flexural strength.

1. Experimental part

1.1 Raw materials

Cement: Onoda P·II 52.5 grade cement.

Steel slag sand: The converter steel slag produced by Shanghai Baosteel is processed by hot stuffing process, with a bulk density of 1910kg/m³, belonging to medium sand, and a fineness modulus of 2.3.

Water reducer: polycarboxylate water reducer (PC) produced by Shanghai Gaotie Chemical Co., Ltd., in powder form.

Latex powder: Model 5010N provided by Wacker Chemicals (China) Co., Ltd.

Defoamer: Code P803 product provided by German Mingling Chemical Group, powder, density 340kg/m³, gray scale 34% (800°C), pH value 7.2 (20°C DIN ISO 976, 1% IN DIST, water).

Cellulose ether: hydroxypropyl methylcellulose ether provided by Kima Chemical Co., Ltd., the one with a viscosity of 2000mPa·s is designated as HPMC2000, and the one with a viscosity of 6000mPa·s is designated as HPMC6000.

Mixing water: tap water.

1.2 Experimental ratio

The cement-sand ratio of the steel slag-sand mortar prepared in the early stage of the test was 1:3 (mass ratio), the water-cement ratio was 0.50 (mass ratio), and the dosage of polycarboxylate superplasticizer was 0.25% (cement mass percentage, the same below. ), the latex powder content is 2.0%, and the defoamer content is 0.08%. For comparative experiments, the dosages of the two cellulose ethers HPMC2000 and HPMC6000 were 0.15%, 0.20%, 0.25% and 0.30%, respectively.

1.3 Test method

Mortar Fluidity Test Method: prepare mortar according to GB/T 17671-1999 “Cement Mortar Strength Test (ISO Method)”, use the test mold in GB/T2419-2005 “Cement Mortar Fluidity Test Method”, and stir Pour the good mortar into the test mold quickly, wipe off the excess mortar with a scraper, lift the test mold vertically upward, and when the mortar no longer flows, measure the maximum diameter of the spread area of the mortar and the diameter in the vertical direction, and take the average value, the result is accurate to 5mm.

The test of the water retention rate of mortar is carried out according to the method specified in JGJ/T 70-2009 “Test Methods for Basic Properties of Building Mortar”.

The test of compressive strength and flexural strength of mortar is carried out according to the method specified in GB/T 17671-1999, and the test ages are 3 days, 7 days and 28 days respectively.

2. Results and discussion

2.1 Effect of cellulose ether on the working performance of steel slag sand mortar

From the effect of different content of cellulose ether on the water retention of steel slag sand mortar, it can be seen that adding HPMC2000 or HPMC6000 can significantly improve the water retention of freshly mixed mortar. With the increase of the content of cellulose ether, the water retention rate of mortar increased greatly and then remained stable. Among them, when the content of cellulose ether is only 0.15%, the water retention rate of the mortar is increased by nearly 10% compared with that without the addition, reaching 96%; when the content is increased to 0.30%, the water retention rate of the mortar is as high as 98.5%. It can be seen that the addition of cellulose ether can significantly improve the water retention of mortar.

From the influence of different dosages of cellulose ether on the fluidity of steel slag sand mortar, it can be seen that when the dosage of cellulose ether is 0.15% and 0.20%, it has no obvious effect on the fluidity of mortar; when the dosage increases to 0.25% or above , has a greater impact on the fluidity, but the fluidity can still be maintained at 260mm and above; when the two cellulose ethers are in the same amount, compared with HPMC2000, the negative impact of HPMC6000 on the mortar fluidity is more obvious.

Hydroxypropyl methyl cellulose ether is a non-ionic polymer with good water retention, and within a certain range, the greater the viscosity, the better the water retention and the more obvious the thickening effect. The reason is that the hydroxyl group on its molecular chain and the oxygen atom on the ether bond can form hydrogen bonds with water molecules, making free water into bound water. Therefore, at the same dosage, HPMC6000 can increase the viscosity of the mortar more than HPMC2000, reduce the fluidity of the mortar, and increase the water retention rate more obviously. Document 10 explains the above phenomenon by forming a viscoelastic solution after cellulose ether is dissolved in water, and characterizing the flow properties by deformation. It can be inferred that the steel slag mortar prepared in this paper has a large fluidity, which can reach 295mm without mixing, and its deformation is relatively large. When cellulose ether is added, the slurry will undergo viscous flow, and its ability to restore shape is small, so lead to a decrease in mobility.

2.2 Effect of cellulose ether on the strength of steel slag sand mortar

The addition of cellulose ether not only affects the working performance of steel slag sand mortar, but also affects its mechanical properties.

From the effect of different dosages of cellulose ether on the compressive strength of steel slag sand mortar, it can be seen that after adding HPMC2000 and HPMC6000, the compressive strength of mortar at each dosage increases with age. Adding HPMC2000 has no obvious effect on the 28-day compressive strength of mortar, and the strength fluctuation is not large; while HPMC2000 has a greater effect on the early (3-day and 7-day) strength, showing a trend of obvious decrease, although the dosage increases to 0.25% and Above, the early compressive strength increased slightly, but still lower than that without adding. When the content of HPMC6000 is lower than 0.20%, the impact on the 7-day and 28-day compressive strength is not obvious, and the 3-day compressive strength decreases slowly. When the content of HPMC6000 increased to 0.25% and above, the 28-day strength increased to a certain extent, and then decreased; the 7-day strength decreased, and then remained stable; the 3-day strength decreased in a stable manner. Therefore, it can be considered that the cellulose ethers with two viscosities of HPMC2000 and HPMC6000 have no obvious deterioration effect on the 28-day compressive strength of mortar, but the addition of HPMC2000 has a more obvious negative effect on the early strength of mortar.

HPMC2000 has different degrees of deterioration on the flexural strength of mortar, no matter in the early stage (3 days and 7 days) or the late stage (28 days). The addition of HPMC6000 also has a certain degree of negative impact on the flexural strength of mortar, but the degree of impact is smaller than that of HPMC2000.

In addition to the function of water retention and thickening, cellulose ether also delays the hydration process of cement. It is mainly due to the adsorption of cellulose ether molecules on cement hydration products, such as calcium silicate hydrate gel and Ca(OH)2, to form a covering layer; moreover, the viscosity of the pore solution increases, and cellulose ether hinders The migration of Ca2+ and SO42- in the pore solution delays the hydration process. Therefore, the early strength (3 days and 7 days) of the mortar mixed with HPMC was reduced.

Adding cellulose ether to the mortar will form a large number of large bubbles with a diameter of 0.5-3mm due to the air-entraining effect of cellulose ether, and the cellulose ether membrane structure is adsorbed on the surface of these bubbles, which to a certain extent plays a role in stabilizing the bubbles. role, thereby weakening the effect of the defoamer in the mortar. Although the formed air bubbles are like ball bearings in the freshly mixed mortar, which improves the workability, once the mortar is solidified and hardened, most of the air bubbles remain in the mortar to form independent pores, which reduces the apparent density of the mortar. The compressive strength and flexural strength decrease accordingly.

It can be seen that when preparing steel slag sand special mortar with high fluidity, high water retention rate and high strength, it is recommended to use HPMC6000, and the dosage should not be greater than 0.20%.

in conclusion

The effects of two viscosities of cellulose ethers (HPMC200 and HPMC6000) on the water retention, fluidity, compressive and flexural strength of steel slag sand mortar were studied through experiments, and the mechanism of action of cellulose ether in steel slag sand mortar was analyzed. The following conclusions:

(1) Regardless of adding HPMC2000 or HPMC6000, the water retention rate of freshly mixed steel slag sand mortar can be significantly improved, and its water retention performance can be improved.

(2) When the dosage is lower than 0.20%, the effect of adding HPMC2000 and HPMC6000 on the fluidity of steel slag sand mortar is not obvious. When the content increases to 0.25% and above, HPMC2000 and HPMC6000 have a certain negative impact on the fluidity of steel slag sand mortar, and the negative impact of HPMC6000 is more obvious.

(3) The addition of HPMC2000 and HPMC6000 has no obvious effect on the 28-day compressive strength of steel slag sand mortar, but HPMC2000 has a greater negative effect on the early compressive strength of mortar, and the flexural strength is also obviously unfavorable. The addition of HPMC6000 has a certain negative effect on the flexural strength of steel slag-sand mortar at all ages, but the degree of effect is significantly lower than that of HPMC2000.