Properties of cement mortar containing recycled glass and rice husk ash

Abstract Using recycled glass (RG) to replace river sand in the production of cement-based materials saves the increasingly depleting natural sand resources. Previous studies have shown that the smooth surface and reactive silica of RG adversely affected its bonding with the cement paste and thereby caused a potential alkali-silica-reaction (ASR). This study used rice husk ash (RHA) as an eco-friendly mineral admixture to ameliorate the properties of the RG incorporated mortar. A fixed replacement of 50% RG was used to replace sand, while varying proportions (10%, 20% and 30%) of RHA were adopted to replace cement. For comparison, a mixture containing only sand and cement was used as the reference sample. The flexural and compressive strength, water absorption, ASR expansion, and rapid chloride mitigation (RCM) of the hardened samples were evaluated. In addition, SEM, XRD, and TG analysis were employed to analyze the microstructures and chemical compositions of different samples. The results showed that incorporating RG as a river sand replacement in cement mortar reduced flexural and compressive strength and increased water absorption and chloride ion penetration. Moreover, the ASR expansion value (0.34%) was beyond the permissible limit (0.1) indicated by the ASTM C1260. The addition of RHA improved the mechanical properties and durability of the cement mortar at a later curing age as a result of the RHA-induced pozzolanic reaction and micro-filler effect. By converting portlandite (CH) derived from cement hydration into secondary C-S-H, the use of RHA greatly reduced the porosity (augmenting the compressive and flexural strength) and concurrently suppressed the RG-induced ASR expansion. The results of XRD, SEM and TG analysis corresponded well with the macro-property analysis and helped to elucidate the underlying mechanisms of the RHA-induced beneficial effects. Findings from this study provide new insights into the potential use of eco-friendly RHA in addressing the mechanical and durability problems associated with the use of RG as aggregate in cementitious materials.