Silica fume is very important in the use of concrete, refractory materials, we all know that the use of the dosage control is very strict, and even in many cases will determine the amount of use through the test, in order to use, in general in the concrete, silica fume dosage of 5% to 10%, as a pumping agent dosage of 2% to 3%, the polymer and insulation mortar dosage of 10% to 15% The amount of silica fume is 5% to 10% in concrete, 2% to 3% as pumping aid, 10% to 15% in polymer and insulation mortar, and the amount of silica fume should be determined according to the liquidity experiment of unshaped refractory castables.
The impact of the amount of silica fume dosage
The dosage of silica fume is so strict, the main reason is that, although silica fume as an admixture can significantly improve the performance of concrete and other materials, but excessive use will make its performance becomes poor, such as concrete if silica fume is mixed in excess, it will cause the cement paste and concrete water demand and increased self-contraction, resulting in a large number of shrinkage cracks, especially in the concrete plane structure.
The factors that determine the amount of silica fume
Silica fume in cement paste and concrete applications there is a range of water-cement ratio, beyond the range, silica fume on hardened cement paste and concrete microstructure improvement will be reduced, so the amount is generally based on this water-cement ratio to determine.
The results of the study prove that at the age of 3 d or 7 d of cement mortar, the strength of mortar specimens containing silica fume with a water-cement ratio less than 0.45 (water-cement ratio of 0.35, 0.40) decreases, while the strength of mortar specimens containing silica fume with a water-cement ratio equal to 0.45 or 0.50 increases;
however, at the age of 28 d or 90 d of cement mortar, the strength of mortar specimens containing silica fume with a water-cement ratio less than 0.35, 0.40, 0.50 The strength of mortar specimens with 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 amount of silica fume is more than 27.5%, silica fume has a significant effect on the development of mortar strength in the later stage.
Silica fume use conditions
Although silica fume can effectively improve the microstructure of hardened cement paste and concrete, but because of the small particle size of silica fume and large specific surface area, so the cement paste and concrete mixed with silica fume, with the increase in the amount of silica fume, water demand increases, since the shrinkage also increases, so the amount of silica fume is generally limited to between 5% and 10%, and use high efficiency water reducing agent to adjust the water demand.
In the use of silica fume in concrete to harden the cement paste and concrete performance of the beneficial effects of the same time, must minimize the adverse effects of silica fume, an effective way to solve this problem is to add silica fume at the same time, mixed with other volcanic ash materials or other substances, so that they complement each other to achieve better technical and economic results.
At present, the use of ultrafine slag and silica fume compounding, or the use of fly ash and silica fume compounding. There are also studies that use silane to pretreat the surface of silica fume and then add to cement paste or concrete, or directly add silane and silica fume at the same time to 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.
It can be seen from the above that the amount of silica fume is not the more the better, more dosage will bring higher strength, but it will affect other technical and economic effects of concrete and other materials, and as an admixture, silica fume can be used with other materials to achieve better results. Henan Superior Abrasives specializes in the research, production and sale of silica fume for various purposes. If you want to buy it, please leave a message on our website or call our customer service for detailed consultation.