Dry co-ball-milled hybrid glass cement for high-volume waste glass mortars

The large-scale utilisation of waste glass in cementitious systems is limited by strength reduction and alkali-silica reaction (ASR) risk at high replacement levels. This study develops a dispersion-controlled hybrid glass cement produced by dry co-ball milling glass powder, binder constituents, and nanomaterials for direct use in mortars containing 100% glass sand. A low-alkali hybrid alkaline binder activated with solid sodium carbonate and sodium citrate was used as the base system. Three dispersion methods, including ball milling, ultrasonication, and high-shear mixing, were compared, followed by optimisation of nanosilica (NS) and graphene nanoplatelet (GNP) dosages. Dry co-ball milling produced higher flowability and compressive strength than wet dispersion methods, indicating improved dispersion effectiveness at the mortar level. The incorporation of 1.5 wt% NS and 0.07 wt% GNPs increased 28-day compressive strength by 27% and 21%, respectively, relative to the control mortar. Accelerated mortar-bar testing showed that the 14-day ASR expansion decreased from 0.25% in the control mortar to below 0.10% in the optimised mixes under ASTM C1260 conditions. Microstructural observations indicate that improvements are mainly associated with matrix densification, pore refinement, and improved particle packing. These findings demonstrate that dry co-ball milling offers a practical strategy for improving the performance of high-volume waste glass mortars.