Influence of nano-SiO2 and steel fiber on mechanical and microstructural properties of red mud-based geopolymer concrete

Red mud-based geopolymer concrete (RMGC) is a new type of green building material widely studied at this stage, which has many advantages such as acceptable early strength, durability, and comprehensive utilization of industrial waste residue. But because of the chemical properties of red mud itself, the performance of RMGC is generally not satisfactory. Therefore, the research on its modified materials and mechanisms has become a hot spot. In this study, RMGC was prepared using red mud, coal gangue, and slag as raw materials. The effects of nano-SiO2 (0–2.5 wt%) and steel fiber (0–1.25 vol%), as well as the effect of the compounding of both on the mechanical properties of RMGC, were investigated, respectively. The microscopic morphology of RMGC was investigated using scanning electron microscopy (SEM). The results showed that the appropriate amount of steel fibers and nano-SiO2 could significantly enhance the performance of the RMGC, either alone or in combination, where the best modification effect can be obtained by mixing the two. On this basis, the mechanism of single and synergistic modification of RMGC by nano-SiO2 and steel fiber was analyzed. The results of this study will enrich the knowledge system of the performance of steel fiber and nano-SiO2 modified geopolymer composites and guide the further promotion and application of red mud-based geopolymer concrete.