In order to make more effective use of silica fume on the improvement of the microstructure of hardened cement paste, many researchers at home and abroad have conducted more detailed studies on the optimal conditions for the application of silica fume in cement paste and concrete, including the water-cement ratio, the amount of silica fume, the selection of admixtures and other volcanic ash admixtures and their dosage.
Silica fume in cement paste and concrete applications there is an optimal water-cement ratio range, generally beyond the range, silica fume on hardened cement paste and concrete microstructure improvement will be reduced.
As a researcher pointed out, at the age of 3 d or 7 d in cement mortar, the water-cement ratio is less than 0.45 (water-cement ratio of 0.35, 0.40) of the mortar specimens containing silica fume strength decreases, while the water-cement ratio is equal to 0.45 或者 0.50 of the mortar specimens containing silica fume strength increases;
but at the age of 28 d or 90 d in cement mortar, the water-cement ratio is less than 0.35, 0.40, 0.50 The strength of mortar specimens containing silica fume is approximately the same;
while the strength of mortar specimens containing silica fume (regardless of the silica fume content) with a water-cement ratio equal to 0.45 is lower;
when the water-cement ratio is equal to 0.50 and the silica fume admixture is greater than 27.5%, silica fume has a significant effect on the later strength development of the mortar.
Although silica fume (硅微粉) can effectively improve the microstructure of hardened cement paste and concrete, but because of the small particle size and large specific surface area of silica fume, so the cement paste and concrete mixed with silica fume, with the increase of silica fume admixture, 需水量增加, and the self-shrinkage also increases. 所以, the amount of silica fume is generally limited to between 5% 和 10%, and high efficiency water reducing agent to adjust the water demand, 同时, there is a compatibility problem between cement, 微硅粉, 外加剂, 所以, when using silica fume must pay attention to its application conditions.
Since the addition of silica fume in concrete may lead to self-shrinkage of concrete, and the addition of silica fume concrete is generally a special requirement of concrete, 所以, the use of silica fume in concrete to harden the cement paste and concrete properties of the beneficial effect at the same time, must minimize the adverse effects brought about by silica fume, the most effective way to solve this problem is the addition of silica fume at the same time mixed with other volcanic ash materials or Other substances, so that they complement each other’s strengths and weaknesses to achieve better technical and economic results. 现在, more research is the use of ultrafine slag and silica fume compounding, or the use of fly ash and silica fume compounding.
Another area of silica fume application conditions are more research is the use of silane on the surface of silica fume pretreatment after mixing into the cement paste or concrete or directly silane and silica fume at the same time into the cement paste or concrete, they can improve the workability of fresh cement paste and concrete, thus improving the microstructure of hardened cement paste and concrete.
