Today, the sustainable development has been deeply rooted in the hearts of the people. The improvement of durability and the utilization of industrial and mining waste slag have become two major themes of concrete scientific research.With the increasing requirements for high-strength and high-performance concrete, the application technology of superfine powder of admixture has been paid more and more attention. The superfine powder of admixture has good filling effect, active effect and micro aggregate effect, which can reduce the rate of hydration heat and hydration heat release, improve the workability, and improve the early strength and corrosion resistance.Guangxi ash has become an essential component of high-strength pumping concrete, and superfine slag powder has gradually been applied in engineering.

1 Research progress of superfine powder of admixture

The superfine powder of concrete admixture refers to the particle size less than 10 μ M, such as mineral powder, fly ash, phosphorus slag powder, etc. After the material reaches the ultra-fine state, its physical properties change, the specific surface area increases, the surface energy increases, and the surface activity increases, which can give full play to the morphological effect, active effect and micro aggregate effect of concrete admixtures.

1.1 Influence of superfine powder on workability and mechanical properties of concrete

The test of Li Hui shows that 40% ultra-fine fly ash (D50=3.09 μ m) When the slump of concrete mixture is higher than that of reference concrete and mixed with ordinary fly ash (D50 ＝ 18.28 μ m) 14.6% and 23.7% respectively; The 7d, 28d and 90d strength of concrete mixed with ultra-fine fly ash is 13.69MPa, 10.2MPa and 13.2MPa higher than that of concrete mixed with ordinary fly ash.Jiang Yonghui studied the influence of the particle distribution of fly ash on the strength of cement by using the grey system method, and pointed out that to improve the strength of fly ash cement, it should increase the proportion of fly ash less than 30 μ M particle content, limited to 30-45 μ M particle content, reduced by more than 45 μ M particle content. According to the theory of composite materials, the strength of cement concrete is mainly related to its submicroscopic structure, and the porosity is the decisive factor to control the strength, so reducing the porosity can greatly improve the strength.The relative particle size significantly affects the packing compactness of the system. The smaller the particle size of mineral admixture, the better its physical filling effect. At the early age, the most probable pore diameter and cumulative porosity of cement-based materials with superfine admixture are smaller than those of cement paste and pure cement paste with ordinary mineral powder. The pore structure of cement-based materials becomes thinner and disconnected, which plays a role in improving the pore structure of the paste and enhancing the compactness at the early age.

1.2 Influence of superfine powder on concrete durability

Guo Shuhui studied the influence of superfine slag powder on the sulfate corrosion resistance of cement mortar. Adding 15% and 25% superfine slag powder can not only increase the strength of cement mortar, but also improve its sulfate corrosion resistance.Gaoyingli have prepared fly ash high-strength lightweight aggregate concrete by using fly ash with fineness of 305m2/kg, 425m2/kg and 550m2/kg respectively. The research results show that when the fly ash content is the same, with the increase of fly ash fineness, the chloride ion permeability and reinforcement resistance of concrete will increase accordingly.The higher the fineness of fly ash is, the more obvious the shrinkage reduction effect is, and the more significant the early crack resistance is. The superfine powder of admixture can significantly improve the pore structure of cement-based materials and improve the compactness of the structure. Improve the pore structure and interface transition zone of concrete, and improve the comprehensive durability of concrete.