Preparation of High Activity Admixture from Steel Slag, Phosphate Slag and Limestone Powder

The problem of low disposal and utilization rate of bulk industrial solid waste needs to be solved. In this paper, a high-activity admixture composed of steel slag-phosphate slag-limestone powder was proposed for most of the solid waste with low activity and a negative impact on concrete workability, combining the characteristics of each solid waste. The paper demonstrates the feasibility and explains the principle of the composite system in terms of water requirement of standard consistency, setting time, workability, and mechanical properties, combined with the composition of the phases, hydration temperature, and microscopic morphology. The results showed that the steel slag:phosphate slag:limestone = 5:2:3 gave the highest activity of the composite system, over 92%. Besides, the composite system had no signi fi cant effect on water demand and setting time compared to cement, and it could signi fi cantly increase the 7 and 28 d activity of the system. The composite system delayed the exothermic hydration of the cement and reduced the exothermic heat but had no effect on the hydration products. Therefore, the research in this paper dramatically improved the solid waste dissipation in concrete, reduced the amount of cement in concrete and positively responded to the national slogan of carbon neutral and peaking.