Study on the synergistic effects of OPC and silica fume on the mechanical and microstructural properties of geopolymer mortar

Abstract

This study investigated the synergistic effects of ordinary Portland cement (OPC) and silica fume (SF) in fly ash-based geopolymer mortar (FA-GPM). The research comprehensively evaluated the impact of replacing fly ash (FA) with varying proportions of OPC and SF on the flowability and mechanical properties of the geopolymer mortar (GPM). Furthermore, this study analyzed the interaction mechanisms of these effects by examining the microstructure and hydration products. The results showed that increasing amounts of SF initially enhanced but subsequently reduced flowability, while the inclusion of OPC consistently decreased it. The combination of SF and OPC significantly improved the mechanical performance and microstructure of the GPM. Optimal mechanical performance, with compressive strengths of 37.66 MPa at 7 days and 50.52 MPa at 28 days, was achieved by adding 10% SF and 20% OPC. Microstructural analysis revealed that using OPC and SF together enhanced the dissolution of alumino-silicate materials in the alkaline activating solution, leading to increased polymerization reactions in the GPM. This process resulted in the formation of calcium-alumino-silicate-hydrate (C-A-S-H) gel, sodium-alumino-silicate-hydrate (N-A-S-H) gel, and calcium-silicate-hydrate (C-S-H) gel, creating a denser structure with reduced porosity and enhanced mechanical properties. This study highlights the advantages of incorporating SF and OPC into FA-GPM, providing valuable insights for further research and practical applications of geopolymer materials.