b. The minimum amount of silica fume: if the amount of silica fume in concrete is too small, the performance of concrete will not be improved. However, if the amount of silica fume is too large, the concrete will be too sticky, difficult to construct, large dry shrinkage deformation and poor frost resistance. Therefore, when adding silica fume, the minimum amount of silica fume should be found out in order to obtain the minimum results. Generally, the effect is satisfactory when the content is less than 10%. The appropriate content of silica fume is generally determined by selecting several silica fume content, such as 3%, 5%, 7% and 10%, forming concrete specimens and drawing r-sf (strength silica fume content) curve according to the silica fume used, cement type and aggregate properties. It is worth noting that the price of silicon powder is high, and the technical and economic indicators should also be considered when determining the minimum content of silicon powder.

c. The best dosage of water reducing agent: if silica fume is used in concrete without water reducing agent, in order to maintain the same fluidity, the water consumption and water cement ratio must be increased, and the strength of concrete mixed with silica fume can not go up, which is also the reason why silica fume was not popularized in concrete in the past. When silica fume is used in combination with water reducing agent, the water cement ratio of silica fume remains unchanged, that is, the water consumption does not increase, but also can achieve the same fluidity as the concrete without silica fume, and the strength and other properties of silica fume concrete have been greatly improved. Generally, naphthalene series high-efficiency water reducing agents are widely used in China, such as Jian 1, h, dh3, FDN, NF, N2b, etc., and their dosage is generally less than 1% of the amount of glue material, Sometimes, in order to reduce the water cement ratio and mix strong concrete, the amount of water reducing agent is up to 2% ～ 3%.

d. Adjustment of sand and stone consumption: generally, the amount of sand and stone does not need to be adjusted. For the addition of silica fume, the volume of sand and stone equal to the volume of silica fume shall be deducted.