超高性能混凝土 has high compressive strength, high resistance to deformation, high density and other characteristics, mainly because of a variety of mineral admixtures added in the formulation process, the more obvious effect is silica fume. The role of silica fume in ultra-high performance concrete is not only to increase the strength, there are other more obvious role.
The role of silica fume in ultra-high performance concrete
Reduce the heat of hydration
When the amount of silica fume is increased, the hydration rate of cementitious material becomes smaller, the peak of hydration exotherm decreases, and the amount of exotherm decreases, which means that the incorporation of silica fume delays the acceleration period of cementitious material and reduces the total amount of exotherm.
Lower calcium hydroxide content
The calcium hydroxide content of the hardened ultra-high performance concrete is inversely proportional to the amount of silica fume. Silica fume reacts with calcium hydroxide and forms secondary hydrated calcium silicate. Silica fume is more reactive and reacts more easily with calcium hydroxide, thus reducing the calcium hydroxide content. When only cement and silica fume are used as cementitious materials and hot curing is used to prepare ultra-high performance concrete, the calcium hydroxide content after hardening is less than 5%, thus reducing the carbonation rate.
Reducing water absorption porosity
The water absorption porosity of ultra-high performance concrete is inversely proportional to the amount of silica fume. The particle size of silica fume is much smaller than that of cement and has volcanic ash activity. The incorporation of silica fume can fill the pores in the hardened ultra-high performance concrete on the one hand, and the C-S-H gel produced by its volcanic ash effect also optimizes the pore size distribution of ultra-high performance concrete and reduces the water absorption porosity. When only cement and silica fume are used as cementitious materials and the ultra-high performance concrete is prepared by hot curing, the capillary pore content of the ultra-high performance concrete is zero.
强度增加
The strength of ultra-high performance concrete is proportional to the amount of silica fume admixture. From the test results of water absorption porosity, it can be seen that the incorporation of silica fume reduces the porosity of UHPC, 所以, the incorporation of silica fume can increase the strength of UHPC. 然而, when the amount of silica fume is too large, the viscosity of fresh UHPC increases and the fluidity decreases, which will increase the porosity of UHPC and reduce the strength of UHPC.
Dosing of silica fume in ultra-high performance concrete
Usually, when adding silica fume, we need to add water-reducing agent, otherwise we need to increase the water consumption (水灰比) if we want to maintain the flow of concrete, which will lead to the strength of concrete is difficult to ensure, but adding water-reducing agent can ensure that the water-cement ratio remains unchanged, to enhance the strength of concrete.
The amount of silica fume
Silica fume in the concrete is too little, not much improvement in concrete performance, but too much, the concrete is too sticky, not easy to construct, and dry shrinkage deformation, poor frost resistance. 所以, when mixed with silica fume, should be used according to the silica fume, cement type and the nature of the aggregate, choose a few doping ratio for concrete specimen analysis, 一般来说, the doping should be less than 10%, many projects on the different requirements of concrete, silica fume doping more than 3% 到 5% 或者.
The amount of water reducing agent
Usually with the use of silica fume water reducing agent are high-efficiency water reducing agent, its dose is generally within 1% of the amount of gel material, sometimes in order to reduce the water-cement ratio of ultra-high performance concrete, water reducing agent dose can reach 2% 到 3%.
It can be seen that the role of silica fume in ultra-high performance concrete is very powerful, but in most cases, 为了满足项目的需要, will also be mixed with some other mineral admixtures, which requires a targeted test to determine before the preparation.
作为中国最大的硅粉供应商之一, 河南优之源 has provided high quality silica fume for many projects using ultra-high performance concrete, 如果你需要, 您可以在我们的网站上留言或致电我们的客服进行详细咨询.
