Silica fume is a by-product of producing silicon metal or ferrosilicon alloys in smelters using electric arc furnaces. These metals are used in many industrial applications to include aluminum and steel production, computer chip fabrication, and production of silicones, which are widely used in lubricants and sealants.
Fresh concrete made with silica fume is more cohesive and therefore less prone to segregation than concrete without silica fume. Too offset this increased cohesion when placing, silica fume concrete is typically placed at 40 to 55 mm greater slump than concrete without silica fume in the same placement.
Also, because of the very high surface area of the silica fume and the usually very low water content of silica fume concrete, there will be very little, if any, bleeding. Once silica fume content of about 5% is reached, there will be no bleeding in most concretes.
In addition to improved durability, the lack of bleeding allows a more efficient finishing process to be used with silica fume concrete flatwork.
Advantages of silica fume in concrete:
1, micro silica fume powder is a neutral inorganic filler with very stable physical properties and chemical properties. It does not contain crystal water and does not participate in curing reaction, and does not affect the reaction mechanism.
2. It has good wettability to all kinds of resins, good adsorption properties, easy mixing and no agglomeration.
3, the size distribution of micro silica fume is reasonable, strong dense, hardness and wear resistance. It can greatly improve the tensile strength, compressive strength, impact strength and wear resistance of the cured products, and the abrasion resistance can be increased by 0.5 to 2.5 times.
4, it can increase the thermal conductivity, change the adhesive viscosity and increase the flame retardancy.
5, it can reduce the exothermic peak temperature of curing reaction of epoxy resin, reduce the linear expansion coefficient and shrinkage rate of solidified products, thereby eliminating internal stress and preventing cracking.
6. Due to the fine grain size and reasonable distribution of the microsilica, it can effectively reduce and eliminate precipitation and stratification.
7. The microsilica fume is pure, the impurity content is low, the physicochemical property is stable, which makes the curing material have good insulation property and anti arc property.
8, the chemical composition of silica fume is silica (SiO2), which belongs to inert material. It has no chemical reaction with most acids and alkaloids. Microsilica is evenly distributed and covered on the surface of objects. It has strong corrosion resistance and cavitation resistance increased by 3 to 16 times.
9, small packing density: one is in 0.2-0.8, one is between 1.0-2.2. As polymer filling material, it can reduce the cost by reducing the amount of loading and saving the amount of polymer.
10, frost resistance: after 300 to 500 cycles of rapid freezing and thawing, the relative elastic modulus of micro silica powder is 10 to 20%, while that of ordinary concrete is 25 to 50 cycles, and the relative elastic modulus is 30 to 73%. Therefore, the frost resistance of concrete can be improved.
11, early strength: silica fume concrete makes the induction period shorten and has the characteristics of early strength.
