Rheology and Fresh-State Performance of Wet-Mix Shotcrete Containing Crushed Glass Aggregate

The increasing demand for sustainable construction materials has intensified interest in alternative fine aggregates for shotcrete production. Crushed glass aggregate (CGA) offers environmental and economic benefits by diverting waste glass from landfills and reducing reliance on natural sand; however, its influence on the fresh-state rheological behaviour of wet-mix shotcrete remains poorly understood. This study investigated the effects of replacing natural sand with a commercially processed angular CGA (particle size approximately 0.1–2.0 mm) at levels of 5–100% by volume on flowability and early-age rheological behaviour using mixtures with constant water content and optimised superplasticiser dosage. Flow table testing was combined with steady-shear and oscillatory rheological measurements to characterise viscosity, shear stress, and viscoelastic transitions relevant to flow initiation. Moderate CGA replacement levels (10–20%) exhibited the most favourable rheological performance, characterised by reduced low-shear viscosity, lower resistance to flow initiation, and earlier viscoelastic transition compared to the control mix. By contrast, high CGA replacement levels (≥75%) exhibited increased low-shear viscosity, stronger elastic behaviour, and delayed or absent viscoelastic transition despite achieving target flow values through admixture adjustment. These results demonstrate that empirical flow tests alone cannot fully capture shear-dependent flow behaviour. Moderate CGA replacement therefore represents a viable pathway for improving shotcrete sustainability while maintaining favourable fresh-state rheological performance.