1. Introduction and classification of self-leveling cement/mortar
Self-leveling cement/mortar is a type that can provide a flat and smooth floor surface on which the final finish (such as carpet, wooden floor, etc.) can be laid. Its key performance requirements include rapid hardening and low shrinkage. There are different floor systems on the market such as cement-based, gypsum-based or their mixtures. In this article we will focus on flowable systems with leveling properties. Flowable hydraulic ground (if it is used as the final covering layer, it is called the surface material; if it is used as the intermediate transition layer, it is called the cushion material) are generally referred to as: cement-based self-leveling floor (surface layer) and cement-based self-leveling floor (cushion layer) ).
2. Product material composition and typical ratio
Self-leveling cement/mortar is a hydraulically hardened composite material made of cement as the base material and highly compounded with other modified materials. Although the various formulas currently available are different and different, but in general the materials
Inseparable from the types listed below, the principle is roughly the same. It is mainly composed of the following six parts: (1) mixed cementitious material, (2) mineral filler, (3) coagulation regulator, (4) rheology modifier, (5) reinforcing component, (6) water composition , the following are typical ratios of some manufacturers.
(1) Mixed cementitious material system
30-40%
High alumina cement
Ordinary Portland Cement
a- hemihydrate gypsum / anhydrite
(2) Mineral filler
55-68%
Quartz sand
calcium carbonate powder
(3) Coagulant regulator
~0.5%
Set retarder – tartaric acid
Coagulant – Lithium Carbonate
(4) Rheology modifier
~0.5%
Superplasticizer-Water Reducer
Defoamer
stabilizer
(5) Reinforcing components
1-4%
redispersible polymer powder
(6) 20%-25%
water
3. Formulation and functional description of materials
Self-leveling cement/mortar is the most complex cement mortar formulation. Generally composed of more than 10 components, the following is the formula of cement-based self-leveling floor (cushion)
Cement-based self-leveling floor (cushion)
Raw Material: OPC ordinary silicate cement 42.5R
Dosage Scale: 28
Raw Material: HAC625 High Alumina Cement CA-50
Dosage Scale: 10
Raw Material: Quartz Sand (70-140mesh)
Dosage Ratio: 41.11
Raw Material: Calcium Carbonate (500mesh)
Dosage Scale: 16.2
Raw Material: Hemihydrate Gypsum semi-hydrated gypsum
Dosage Scale: 1
Raw Material Raw material: Anhydrite anhydrite (anhydrite)
Dosage Scale: 6
Raw Material: Latex Powder AXILATTM HP8029
Dosage Scale: 1.5
Raw Material: Cellulose Ether HPMC400
Dosage Scale: 0.06
Raw Material: Superplasticizer SMF10
Dosage Scale: 0.6
Raw Material: Defoamer defoamer AXILATTM DF 770 DD
Dosage Scale: 0.2
Raw Material: Tartaric Acid 200 mesh
Dosage Scale: 0.18
Raw Material: Lithium Carbonate 800 mesh
Dosage Scale: 0.15
Raw Material: Calcium Hydrate Slaked Lime
Dosage Scale: 1
Raw Material: Total
Dosage Scale: 100
Note: Construction above 5°C.
(1) Its cementitious material system is generally composed of ordinary Portland cement (OPC), high alumina cement (CAC) and calcium sulfate, so as to provide enough calcium, aluminum and sulfur to form calcium vanadium stone. This is because the formation of calcium vanadium stone has three main characteristics, namely (1) fast formation speed, (2) high water binding capacity, and (3) ability to supplement shrinkage, which is fully in line with the macroscopic properties that self-leveling cement/mortar must provide Require.
(2) The grading of self-leveling cement/mortar particles requires the use of coarser fillers (such as quartz sand) and finer fillers (such as finely ground calcium carbonate powder) in combination to achieve the best compactness effect.
(3) The calcium sulfate produced in self-leveling cement/mortar is -hemihydrate gypsum (-CaSO4•½H2O) or anhydrite (CaSO4); they can release sulfate radicals at a fast enough rate without increasing water consumption . A question that is often asked is why -hemihydrate gypsum (which has the same chemical composition as -hemihydrate), which is more readily available and less expensive than -hemihydrate, cannot be used. But the problem is that the high void ratio of -hemihydrate gypsum will significantly increase the water consumption, which will lead to a decrease in the strength of the hardened mortar.
(4) Redispersible rubber powder is the key component of self-leveling cement/mortar. It can improve fluidity, surface abrasion resistance, pull-out strength and flexural strength. In addition, it reduces the modulus of elasticity, thereby reducing the internal stress of the system. Redispersible rubber powders must be able to form strong polymer films. High-performance self-leveling cement/mortar products contain up to 8% redispersible rubber powder, and are mainly high-alumina cement. This product guarantees rapid setting hardening and high early strength after 24 hours, thus meeting the requirements for next-day construction work, such as renovation works.
(5) Self-leveling cement/mortar requires setting accelerators (such as lithium carbonate) to achieve early cement setting strength, and retarders (such as tartaric acid) to slow down the setting speed of gypsum.
(6) Superplasticizer (polycarboxylate superplasticizer) acts as a water reducer in self-leveling cement/mortar and thus provides flow and leveling performance.
(7) The defoamer can not only reduce the air content and improve the final strength, but also obtain a uniform, smooth and firm surface.
(8) A small amount of stabilizer (such as cellulose ether) can prevent the segregation of the mortar and the formation of the skin, thus causing a negative impact on the final surface properties. Redispersible rubber powders further improve flow properties and contribute to strength.
4. Product quality requirements and key technologies
4.1. Basic requirements for self-leveling cement/mortar
(1) It has good fluidity, and has good leveling property in the case of a few millimeters thick, and
The slurry has good stability, so that it can minimize adverse phenomena such as segregation, delamination, bleeding, and bubbling.
And it is necessary to ensure sufficient usable time, usually more than 40 minutes, so as to facilitate construction operations.
(2) The flatness is better, and the surface has no obvious defects.
(3) As a ground material, its compressive strength, wear resistance, impact resistance, water resistance and other physical mechanics
The performance should meet the requirements of general indoor building ground.
(4) Durability is better.
(5) The construction is simple, fast, time-saving and labor-saving.
4.2. Main technical properties of self-leveling cement/mortar
(1) Mobility
Fluidity is an important indicator reflecting the performance of self-leveling cement/mortar. Generally, the fluidity is greater than 210-260mm.
(2) Slurry stability
This index is an index reflecting the stability of self-leveling cement/mortar. Pour the mixed slurry on a glass plate placed horizontally, observe after 20 minutes, there should be no obvious bleeding, delamination, segregation, bubbling and other phenomena. This index has a great influence on the surface condition and durability of the material after molding.
(3) Compressive strength
As a ground material, this indicator must comply with the construction specifications for cement floors, domestic ordinary cement mortar surfaces
The compressive strength of the first floor is required to be above 15MPa, and the compressive strength of the cement concrete surface is above 20MPa.
(4) Flexural strength
The flexural strength of industrial self-leveling cement/mortar should be greater than 6Mpa.
(5) Coagulation time
For the setting time of self-leveling cement/mortar, after confirming that the slurry is evenly stirred, ensure that its use time is more than 40 minutes, and the operability will not be affected.
(6) Impact resistance
Self-leveling cement/mortar should be able to withstand the impact of human body and transported items in normal traffic, and the impact resistance of the ground is greater than or equal to 4 joules.
(7) Wear resistance
Self-leveling cement/mortar as a ground surface material must withstand normal ground traffic. Due to its thin leveling layer, when the ground base is solid, its bearing force is mainly on the surface, not on the volume. Therefore, its wear resistance is more important than compressive strength.
(8) Bond tensile strength to the base layer
The bonding strength between self-leveling cement/mortar and the base layer is directly related to whether there will be hollowing and falling off after the slurry is hardened, which has a greater impact on the durability of the material. In the actual construction process, brush the ground interface agent to make it reach a condition that is more suitable for the construction of self-leveling materials. The bonding tensile strength of domestic cement floor self-leveling materials is usually above 0.8MPa.
(9) Crack resistance
Crack resistance is a key indicator of self-leveling cement/mortar, and its size is related to whether there are cracks, hollowing, and falling off after the self-leveling material hardens. Whether you can correctly evaluate the crack resistance of self-leveling materials is related to whether you can correctly evaluate the success or failure of self-leveling material products.
5. Construction of self-leveling cement/mortar
(1) Basic treatment
Clean up the base layer to remove floating dust, oil stains and other unfavorable bonding substances. If there are large potholes in the base layer, filling and leveling treatment is required.
(2) Surface treatment
Apply 2 coats of ground interface agent on the cleaned base floor.
(3) Leveling construction
Calculate the amount of various materials according to the amount of materials, water-solid ratio (or liquid-solid ratio) and construction area, stir evenly with a mixer, pour the stirred slurry on the ground, and gently scrape the stubble.
(4) Conservation
It can be maintained according to the requirements of various self-leveling materials.
Post time: Dec-06-2022