applications of microsilica in concrete
The micro silica powder as a blending agent in the concrete industry is an area in which the use of silica fume at home and abroad is early, most successful and the most wide used. Due to the fine particle size, large specific surface area and high pozzolanic activity, the microsilica can be used as an additive to prepare high strength concrete. The addition of micro silica powder to concrete can improve the multifaceted properties of concrete as following:
Foreign studies have shown that when the substitution rate of micro silica powder to cement is less than 30%, the steaming temperature is 80℃, and the compressive strength of mortar is twice that of non-microsilica powder(100MPa); If adopting autoclaved curing, it is almost three times(150MPa). Canadian studies have shown that when microsilica is used in combination with super-plasticizer, the compressive strength of concrete is 3 to 5 times that of non-silicon doping. At present, the United States, Denmark, Norway and other countries have silica fume as a blending agent to prepare concrete with a strength of up to 1100kg／cm2 with simple process. The effect of micro silica powder in concrete increases with the amount of micro silica powder, and the effect of activity and particles on concrete strength is gradually enhanced.
Micro silica powder adding into the concrete can increase the silicon content of the reaction. Under the electron microscope, crystal growth occurs in the voids of the cement stone mixed with microsilica concrete. In addition, the silica fume particles are fine, uniformly filling the concrete micro pores, reducing the micro-empty volume so as to enhancing the compactness.
★Improve concrete segregation and bleeding performance
Foreign studies have proved that the more the microsilica is mixed, the more difficult it is for the concrete material to segregate and bleed. When the substitution rate reaches 15%, the concrete slump doesn’t produce segregation and bleeding even if it reaches15-20cm, when the substitution rate reaches 20%-30%, it is not easy to isolate the concrete directly into the tap water.
★Improve the impermeability, chemical resistance and specific resistance of concrete.
Since the incorporation of microsilica improves the compactness of concrete and greatly reduces the voids of cement stone, the impermeability of micro silica powder concrete is improved. Domestic and foreign studies believe that when the silica fume substitution rate in concrete is 10%-20%, the impermeability and chemical resistance of concrete are significantly improves, and the corrosion resistance of steel bars is also improved. Due to the improvement of compactness and the increase of SiO2content, it prevents effectively the intrusion and corrosion of acid ions. In addition, because of the high specific resistance of silica fume, the specific resistance of concrete can be increased by 1.9-16 times, which is beneficial to protect steel bars and embedded parts.