Mix Design Of Silica Fume Concrete

wallpapers Robot Tech 2021-01-29
Silica fume, also called micro-silica fume, scientific name "silica fume", is made by special trapping device to collect and process the smoke and dust escaping from exhaust gas during the process of smelting industrial silicon and ferrosilicon at high temperature in industrial electric furnace. In the escaping smoke and dust, the content of SiO2 accounts for about 90% of the total smoke and dust. The particle size is very small, and the average particle size is almost nanometer level, so it is called silica fume.
 
Mix ratio
 
For the design of the mixing ratio of silica fume concrete, it is mainly based on the design requirements to determine the mixing method of silica fume, the optimal amount of silica fume, the optimal amount of water reducing agent and the adjustment of sand and gravel materials, while the others are based on ordinary concrete. The design method is carried out.
 
a) The mixing method of silica fume: There are generally two methods for 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 silica fume instead of cement, and is divided into equal replacement and partial equal replacement. The equal replacement is the silica fume content instead of the equal cement, and the partial replacement is 1 kg silica fume instead of 1~3 kg cement. As a research, the general mixing amount is 5%~30%, and the water-cement ratio generally remains unchanged: while the external mixing method refers to that the silica fume is mixed into the concrete like an admixture, and the amount of cement is not reduced, the mixing amount is generally 5% ~10%. Generally, the mechanical properties of concrete obtained by the external mixing method are much higher, but the amount of cementing material in the concrete is increased.
 
b) The optimum amount of silica fume: Too little amount of silica fume in the concrete 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 will be large and the frost resistance will be poor Therefore, when adding silicon powder, the optimal dosage should be found to obtain the best results. In general, the effect is more satisfactory if the dosage is less than 10%. The appropriate amount of silica fume is generally selected according to the 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 (strength- The silicon powder content) curve is determined. It is worth noting that the price of silica fume is relatively high, and technical and economic indicators should also be considered when determining the optimal amount of silica fume.
 
c) Optimal dosage of water-reducing agent: When using silica fume in concrete, if you want to maintain the same fluidity without adding water-reducing agent, you must increase the water consumption, increase the water-cement ratio, and increase the strength of concrete with silica fume It can't go up, which is the reason why silica fume has not been popularized in concrete in the past. The water-cement ratio of silica fume and water-reducing agent mixed with silica fume remains unchanged, that is, the water consumption does not increase, and the same fluidity as concrete without silica fume can be achieved, and the strength of silica fume concrete is greatly improved. In general, naphthalene-based superplasticizers, such as Jian 1, H, DH3, FDN, NF, N2B, etc., are generally used in China. The dosage is generally within 1% of the amount of glue. Sometimes in order to reduce the water-cement ratio, mix To make super high-strength concrete, the amount of water reducing agent can reach 2%~3%.
 
d) Adjustment of the amount of sand and gravel: Generally, the amount of sand and gravel does not need to be adjusted when the silica fume is added. The volume of sand and gravel equal to the volume of silica fume should be deducted for the externally mixed silica fume.
 
Production Process
 
There are many methods for preparing silicon powder from silicon blocks. Among them, the Raymond method, the counter-roll method, the disc grinding method and the punching and spinning method are more effective and widely used. The equipment used is Raymond method, roller mill, disc mill (also called vertical mill) and punching and spinning method. In terms of the principle of milling, the first three are extrusion crushing, and the latter is impact crushing. In terms of their structure, they are very different, each with its own characteristics, and each has its own advantages and disadvantages.

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