Synergistic Effects of Silica Fume on the Mechanical and Thermal Stability Performance of Geopolymer Composite Mortars

Geopolymer materials have attracted considerable interest due to their economic, engineering, and environmental advantages. As global industrialization intensifies and infrastructure demands increase, the need for sustainable and alternative construction materials has become more urgent. Despite the considerable potential of Bottle Glass Powder (WBGP) incorporating Ground Blast Furnace Slag (GBFS)-based geopolymer materials, further research is required to improve their mechanical properties, reduce porosity, and enhance their resistance to elevated temperatures through effective modification of the binder system. In response to this challenge, the present study aims to develop high-performance geopolymer mortars by incorporating silica fume (SF) as a partial replacement for GBFS, with the goal of improving the performance of WBGP-based geopolymer systems. These were activated using a low-molarity sodium hydroxide solution in combination with sodium silicate and subsequently cured at ambient temperature. The influence of varying SF content on the mechanical, physical, and microstructural characteristics of WBGP-based geopolymer was evaluated using flexural, compressive, and tensile strength measurements, along with advanced analytical techniques, including XRD and FTIR. Furthermore, the durability characteristics of the developed geopolymer, including porosity and resistance to elevated temperatures (800 °C), were evaluated. The findings indicated that incorporating 3% and 6% SF as a replacement for GBFS enhanced strength performance. At the optimal mix containing 6% SF, the reported results showed enhanced bond strength between binder components, yielding a compressive strength of 36.2 MPa after 56 days, compared with 29 MPa for the control specimen. The substitution of GBFS by 6% of SF substantially reduces the geopolymer porosity and increases its resistance to elevated temperatures. These results offer valuable guidance for incorporating SF into the design and formulation of WBGP-GBFS geopolymer mortars, adding to the progression of sustainable and high-performance construction materials.