Micro-silica is finely processed from silicon dioxide (SiO2), also known as quartz, through crushing, purification, grinding, grading and other processes. It has high purity, white colour, and reasonable particle size distribution. It has unique properties and a wide range of uses.
Because the micro-silica fume can fill the pores between cement particles and, at the same time, form a gel with the hydration product and react with the alkaline material magnesium oxide to form a gel. In cement-based concrete, mortar, concrete and refractory castables, mixing a proper amount of micro-silica fume silica fume can play the following roles:
1. Significantly improve the compression resistance, flexural resistance, impermeability, corrosion resistance, impact resistance and wear resistance.
2. It has the functions of retaining water, preventing segregation and bleeding, and greatly reducing the resistance of concrete pumping.
3. Significantly prolong the service life of concrete. Especially in harsh environments such as chloride pollution erosion, sulfate erosion, and high humidity, the durability of concrete can be doubled or even several times higher.
4. Significantly reduce the floor ash of sprayed concrete and castables and increase the thickness of a single spray layer.
5. It is a necessary component of high-strength concrete, and C150 concrete has been used in engineering.
6. It has about five times the effect of cement, and its application in ordinary concrete and low-cement castables can reduce costs and improve durability.
7. Effectively prevent the occurrence of concrete alkali-aggregate reactions.
8. Improve the compactness of castable refractories. When coexisting with Al2O3, it is easier to form a mullite phase, which increases its high-temperature strength and thermal shock resistance.
The design of the mixing ratio of micro-silica fume concrete is mainly based on the design requirements to determine the method of mixing silica fume with the optimal amount of micro-silica.
Ordinary concrete design method
1. The method of mixing silica fume: There are generally two methods for micro-silica fume in concrete: one is internal mixing, and the other is external mixing, both of which are used in conjunction with a water-reducing agent. The internal mixing method often uses micro-silica fume instead of cement and is divided into equal replacement and partial equal replacement. The equal replacement is micro-silica fume content instead of equal cement, and the partial replacement is 1 kg micro-silica fume instead of 1～3. Kg cement, as a research, the general mixing amount is 5% to 30%, and the water-cement ratio generally remains unchanged, while the external mixing method refers to the micro-silica fume is mixed into the concrete like an admixture, and the amount of cement is not reduced. Generally, it is 5% to 10%. Generally, the mechanical properties of concrete obtained by the external admixture method are much higher, but the amount of cementing material in the concrete is increased.
2. The optimum amount of silica fume: Too little silica fume is added to the concrete, which will not improve the performance of the concrete much, but if the amount is too much, the concrete will be too sticky and difficult to construct, and the shrinkage deformation will be large, and it will resist freezing Poor performance, therefore, when doping micro-silica powder, the optimal dosing amount should be found in order to obtain the best results. Under normal circumstances, the effect is more satisfactory if the dosage is less than 10%. The appropriate amount of micro-silica fume is generally selected according to the micro-silica fume, the type of cement and the nature of the aggregate, such as 3, 5, 7, 10%, etc., to form the concrete specimen and draw R-SF (Intensity-micro silica content) curve is determined.
3. The optimal dosage of water-reducing agent: Use micro-silica fume in concrete. If you want to keep the same fluidity without adding a water-reducing agent, you must increase the water consumption and the water-cement ratio. Combined use of micro-silica fume and water-reducing agent. The water-cement ratio of mixed micro-silica fume remains unchanged; that is, the water consumption does not increase, and the same fluidity and strength of micro-silica concrete can be achieved with concrete without micro-silica fume. Has been greatly improved.
4. Adjustment of the amount of sand and gravel: Generally, there is no need to adjust the amount of sand and gravel mixed with micro-silica powder. The volume of sand and gravel equal to the volume of the micro-silica powder should be reduced when the micro-silica powder is added.
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