Waste Glass Powder as a Circular-Economy Precursor in Geopolymer Binders

The transition toward low-carbon and resource-efficient construction materials has intensified interest in geopolymer binders incorporating industrial and post-consumer wastes. Waste glass powder (WGP), a silica-rich component of the global glass waste stream, has emerged as a promising circular-economy precursor in alkali-activated systems; however, reported durability trends remain inconsistent and are often interpreted without mechanistic integration. This review synthesises current knowledge of WGP reactivity, gel chemistry, and long-term performance through an explicit reaction–transport–ageing (R–T–A) framework that links dissolution behaviour and phase assemblage development to pore connectivity, ion ingress, and time-dependent degradation. Under alkaline activation, the amorphous structure of WGP promotes silica release, modifying Si/Al ratios and governing the formation of N-A-S-H or hybrid N-A-S-H/C-(A)-S-H gels. These reaction products determine transport characteristics and ageing evolution, which collectively control chemical resistance, chloride ingress, alkali–silica reaction-type instability, and dimensional stability. Variability across studies is shown to arise from imbalances in particle fineness, replacement level, precursor chemistry, and activator design rather than intrinsic inconsistency in WGP behaviour. The R–T–A framework clarifies how reaction completeness, pore network architecture, and long-term phase stability interact to produce system-dependent durability outcomes. WGP demonstrates strong potential as a circulareconomy precursor in alkali-activated binders; however, reliable structural application requires durability-informed mix design grounded in coupled reaction–transport–ageing mechanisms and supported by extended exposure testing under realistic service conditions.