Effects of steel slag content on the performance of alkali-activated coal gangue-slag mortar

To address the significant shrinkage issue of alkali-activated materials (AAMs) and to utilize industrial solid waste, this study used steel slag (SS), coal gangue (CG), and ground granulated blast furnace slag (GGBFS) as the raw materials, maintaining the proportion of GGBFS at 50% to guarantee fundamental strength, and substituting a portion of CG with SS to formulate alkali-activated coal gangue-slag mortar (ACGM). Based on existing research, this study examined the mechanical characteristics and desiccation contraction of ACGM with various SS proportions. In addition, microscopic analyses were employed to analyze the impact of SS on the reaction processes and structural evolution of ACGM. The results demonstrated that when 40% SS was added, more gel and ettringite were produced in the system. These products interwove to form a dense microstructure while inhibiting gel deformation, leading to a 41.7% increase in the 28-day compressive strength regarding ACGM. Furthermore, the 28-day drying shrinkage associated with ACGM was reduced by 28.9%. This improvement was attributed to the addition of SS, which slowed the decrease in internal relative humidity. Additionally, the formation of ettringite inhibited matrix deformation and reduced drying shrinkage. However, incorporating 50% SS was found to inhibit both mechanical strength development and drying shrinkage reduction. The utilization of SS in ACGM provided a pathway for large-scale application of SS in AAMs, offering novel insights for mitigating shrinkage in AAMs.