Utilization of Desulfurization Gypsum in Alkali-Activated Mortar: Performance Enhancement and Microstructural Evolution

The engineering applicability of alkali-activated mortar (AAM) is limited by high shrinkage and fast setting time. In this study, the shrinkage performance of AAM was regulated by adding desulfurization gypsum (DG), and the effects of DG content on its workability, corrosion resistance, and mechanical properties were systematically investigated. The test included fluidity, setting time, compressive strength, drying shrinkage, water erosion resistance, and sulfate erosion resistance and was combined with microscopic analysis to reveal its phase composition and micro-morphology. The results show that DG can significantly prolong the setting time and reduce the drying shrinkage. With a DG content of 10%, alkali-activated materials exhibited a setting time similar to that of OPC, and the 56-d drying shrinkage of the AAM was reduced by 20.2%. However, the fluidity, water erosion resistance, and sulfate resistance decreased with an increase in DG content. When the DG content was 10%, the fluidity of the AAM reached 126 mm, and its setting time was equivalent to that of OPC. The mechanical properties showed a trend of increasing first and then decreasing. The optimum was reached when the DG content was 6%. The 28-d compressive strength of AAM-6 was 63.25 MPa, and after 60 days of water erosion and sulfate corrosion its residual strength was still higher than that of OPC in the same environment. Microscopic analysis showed that DG promoted the formation of ettringite, which filled pores with age and formed a dense structure, thereby improving mechanical properties and inhibiting shrinkage. This study enhances the engineering applicability of AAM while enabling high-value utilization of industrial solid waste for sustainable construction materials.