Concrete sanding penetrant
1、 Main causes of sand on concrete surface There are many reasons for sanding on the concrete surface, the main reasons are ：
one cement Improper variety and low cement consumption.
2. The water cement ratio is too large: that is, the amount of water in the mixed concrete is large, which causes bleeding on the concrete surface and reduces the strength of the concrete surface.
three sand The material grading is unreasonable and the mud content is high: the unreasonable aggregate grading and too fine soil sand are also easy to lead to ground sanding, which affects the early hydration of cement and the setting of concrete.
4. Excessive vibration during construction: increase bleeding on the concrete surface, resulting in low strength of the concrete surface.
5. Improper maintenance.
6. The calendering time is not well controlled, the concrete surface is not up to a certain strength, and the construction concrete surface is frozen under low temperature.
7. If the service life is too long, the aging wear will also cause sanding.
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2、 Concrete penetrant used for sand removal treatment
two point one Action mechanism
(1) Infiltration curing: effective penetration of 3~10mm, chemical reaction with substances in the concrete, forming a dense whole; Compressive strength increased by 30-40%, effectively improving hardness and density;
(2) Wear resistance and hardening: effectively improve the hardness, density and wear resistance of concrete, and prevent the concrete surface from sanding and loosening
(3) Sealing and dust-proof: penetrate into the concrete for deep sealing, extend the service life of the concrete floor, and make the floor easier to clean and maintain.
two point two Operation steps
l Base course requirements
The sanding ground shall be cleaned, free of floating ash and kept dry (damp is allowed, but there shall be no open water);
l Base course strengthening treatment
(1) Spray penetrant to ensure that the base course is fully soaked and absorbed, so that the whole ground is completely saturated; There should be no surplus material accumulation;
(2) The ground with serious sanding can be sprayed three times continuously.
3、 Engineering application
In recent years, due to various reasons, concrete ground sanding has become a common quality problem in the construction industry. Concrete penetrant is directly painted on the sanded concrete with transparent liquid, which can effectively increase the hardness of the sanded ground without changing the original concrete color. Because of its advantages of simple operation and low cost, it has been widely used in school playground, factory floor The accumulated use area of sanding treatment for concrete parts such as underground garage and community pavement has exceeded 8 million square meters.
4、 How to prevent ground sanding
l Strictly control the water cement ratio
The water cement ratio directly affects mortar strength. If the water cement ratio is too large, the ground strength is low, the ground surface is rough, not wear-resistant, and easy to sand; Excess free water evaporates, resulting in pores on the surface of cement slurry, which reduces the compactness of mortar and is easy to wear and sand.
l Use ordinary Portland cement as much as possible ( Strength grade not less than 42.5MPa)
Compared with slag cement and pozzolanic cement, ordinary Portland cement has the advantages of good water retention, small drying shrinkage and high early strength, which is beneficial to ensure the ground quality and construction progress. The use of ordinary Portland cement is the prerequisite to ensure the strength of cement mortar and prevent sanding on the floor.
l It is prohibited to use expired cement and damp cement
Cement stored for more than three months is called expired cement. When the expired cement is used for the ground surface course, its strength, hardness and wear resistance will be significantly reduced, resulting in sanding. Damp cement is the cement and water coagulate into blocks, which greatly reduces the activity and poor cementation performance. Compared with expired cement, the quality is worse, so it cannot be used on the ground surface.
l Do not use fine sand for ground surface mortar
The ground must have certain strength and wear resistance to withstand various pressures, friction and impacts. Coarse sand and medium sand are superior to fine sand in strength and wear resistance. The mortar mixed with fine sand has large drying shrinkage and is easy to crack. Water retention is also poor, which is not conducive to calendering. The silt content of sand shall not be more than 3%, otherwise the strength of mortar will be reduced, resulting in sanding on the floor.
l Master the calendering time
Cement mortar shall be compacted as it is laid, leveled with wood trowel and polished with iron trowel. Calendering shall be completed before final setting. If the calendering is too early, the surface will float a layer of water, which will inevitably affect the mortar strength; If the calendering time is too late, it will disturb or damage the setting structure of cement gel, affect the growth of mortar strength, and the surface pores are difficult to eliminate, which will also lead to sanding.
l Sufficient curing time
The quality of maintenance is closely related to the quality of the ground. The general curing time should be more than 7 days. If the curing time is not enough, the moisture will continuously evaporate in the dry air, which will slow down or even stop hardening. The surface mortar will not reach the design strength, and sanding is inevitable. Similarly, early use when the strength is low will inevitably interrupt the curing, affect the strength growth and damage the surface.
l Winter construction of cement floor
During winter construction, the surface layer is thin and should be protected from freezing. Ensure that the temperature of the construction environment is above 5 ℃. After the mortar is frozen, its volume expands, resulting in the increase of void ratio and the formation of loose particles. The strength of the surface layer will be greatly reduced, and sanding will occur during use.
