Study on multi-objective matching ratio optimization and strength development law of basalt stone powder composite cementitious materials

Abstract

In order to better apply basalt powder to supplement cementitious materials ( SCMs), this paper chooses the content of basalt powder, fly ash and slag as the influencing factors, and the early strength ( 3d, 7d) and long-term strength ( 28d, 60d) of mortar as the evaluation index of SCMs. Based on the response surface and multi-objective optimization method, the Box-Benken experimental design method was used to study the influence of physical and chemical superposition between various factors on the strength development and optimize the ratio.The low-field nuclear magnetic resonance technique was used to detect the water change and porosity difference between the reference group and the optimization group at each age. The results show that the content of stone powder and fly ash has a significant effect on the early and long-term strength, the slag only has a significant effect on the early strength, the interaction between the three has no significant effect on the early and 60 d strength, and the interaction between stone powder and slag has a significant effect on the 28 d strength. The optimal compatibility of basalt stone powder-assisted cementitious materials is stone powder ( 10%), fly ash ( 5%), and slag ( 25.11%). Under this mix ratio, the strength activity index of mortar at each age meets the requirements. In the early hydration process, the physical filling effect of supplement cementitious materials such as stone powder in the optimization group can better optimize the pore structure inside the slurry, and the strength improvement is slower than that of the reference group. In the later stage of hydration, the number of hydration products in the optimized group increased, and the strength increased significantly, which was closer to the strength of the benchmark group.