Self-leveling mortar is a dry-mixed powder material. After processing, it can be used after mixing with water on site. As long as it is pushed away with a scraper, a high-quality base surface can be obtained. The characteristics are as follows;
The hardening speed is fast, and you can walk on it within 24 hours
Because it works fast, it doesn’t waste time doing other work.
Judging the quality of self-leveling mortar can be judged from the following aspects:
1. High fluidity, cohesiveness, no bleeding and segregation.
2. The strength and final compressive strength after grinding meet the requirements
3. The dimensional change rate is small (that is, no expansion and no shrinkage).
4. Under the condition of low water-cement ratio, it has good rheology;
5,, reach the national standard of 24h compressive strength greater than 6.0MPa, flexural strength greater than 2.0MPa.
Self-leveling cement reference formula
Raw materials Additives
42.5 300
plaster 50
heavy calcium 150
Sand 500
Rubber powder 10
Polycarboxylate 0.5
sm 2.5
p803 0.5
mc400 0.7
Tartaric acid 0.8
The amount of water added is 24% and the fluidity reaches 145~148
Sometimes if the mixing time is not enough, there will be oil spots, white spots, precipitation, bleeding, powder loss, strength, etc., which need to be paid attention to in the raw materials of the formula. Let’s analyze them one by one.
A. How to prevent oil spots
remove tartaric acid
For example, P803, this raw material may cause oil spots, we usually pre-mix P803 with 1 times of sand and 1 times of calcium carbonate to reduce oil spots.
B, how to prevent subsidence
1. Reduce the amount of water reducing agent,
2. Properly increase the amount of cellulose ether added,
3. Adjust the gradation of the sand.
C, how to prevent insufficient strength
1. The amount of high alumina cement is low, and the 1d strength is not up to standard;
2. The amount of rubber powder is too low;
3. Too much retarder is added;
4. The formulation system is unstable, resulting in self-leveling bleeding
D, how to prevent white spots
1. The additive particles are too coarse
2. There is agglomeration of raw materials.
E, the principle of raw material addition:
1. Heavy calcium is mixed with high alumina cement to generate calcium carbonoaluminate, which can improve the compressive strength.
2. Water reducing agent can reduce the amount of water and cement, and improve the strength and durability of concrete;
3. Methyl cellulose is used as a water-retaining agent to effectively avoid the defect of self-leveling mortar that loses water quickly due to a thin flow layer;
4. Using anhydrite as an expansion agent and using hexanediol as a reducing agent synergizes to effectively compensate for shrinkage. This formula explores the distribution ratio of each component, and the fluidity of the prepared cement-based self-leveling mortar is greater than 130mm in 20 minutes.