In-Depth Insight into the Effects of Steel Slag and Calcium Hydroxide on the Properties of a Fly Ash–Red Mud Geopolymer.

The low mechanical strength of a low-calcium fly ash (FA)–red mud (RM) geopolymer severely limits its application. Steel slag (SS) and Ca(OH)₂ can provide calcium and alkali for the hydration process of a low-calcium FA-based geopolymer. In this study, SS was used to replace part of the RM, and Ca(OH)₂ was introduced. The effects of SS and Ca(OH)₂ on the properties of the FA-RM geopolymer were investigated. The experimental results show that SS promoted the matrix to generate more C(N)-A-S-H and C-S-H gels and optimized the pore structure, thereby improving the mechanical properties of the FA-based geopolymer. The addition of 4 wt.% Ca(OH)₂ increased the hydration products of the FA-based geopolymer, the microstructure was denser, and the mechanical properties were significantly improved. The 28 d compressive strength of the FA-based ternary composite geopolymer prepared by replacing part of the RM with SS and adding Ca(OH)₂ reached 30.6 MPa, which provided an experimental basis for the resource utilization of various bulk solid wastes. [ABSTRACT FROM AUTHOR]