Synergic utilization of waste glass powder for fire-resilient and low alkali-activated concrete

Ordinary Portland Cement (OPC) concrete suffers severe degradation at high temperatures, and its production carries a significant carbon footprint, necessitating sustainable, fire-resilient alternatives. This study evaluates an Alkali-Activated Concrete (AAC) system based on Fly Ash (FA) and Ground Granulated Blast Furnace Slag (GGBFS), where Waste Glass Powder (WGP) was systematically investigated as a precursor replacement. Key variables included a 25% WGP replacement for FA or GGBFS and varied NaOH concentrations (8–10%). Specimens were tested for residual mechanical performance (compressive strength, stress-strain, ductility, energy absorption) after exposure to temperatures up to 1000 °C. Crucially, replacing 25% of fly ash with WGP (Mix M 3 C 5 ) yielded the highest ambient compressive strength (68.61 MPa) with a reduced alkali demand of only 8% NaOH. This significantly surpassed the baseline FA-GGBFS control mix (M 1 Na 10 ), which required 10% NaOH to achieve a lower peak strength of 53.16 MPa. Furthermore, the optimized WGP formulation (M3C5) demonstrated excellent thermo-mechanical stability, retaining 40.3% of its strength (27.66 MPa) at 1000 °C. This represents a superior residual load-bearing capacity compared to the baseline M1Na10 mix (24.25 MPa) and exhibited superior ductility compared to the baseline mixes at extreme temperatures. Microstructural analyses (XRD, SEM, EDS) confirmed that WGP promoted a denser, more homogeneous, silica-rich gel matrix, which mitigated thermal microcracking and explained the enhanced performance. This work establishes WGP as a synergistic precursor in AAC, enabling the production of high-performance, fire-resilient concrete with reduced alkali requirements. This strategy effectively valorizes waste glass, contributes to a lower-carbon built environment and supports the principles of a circular economy.