Sustainable mortar with waste glass fine aggregates and pond ash as an alkali-silica reaction suppressor

The construction industry seeks sustainable alternatives to conventional materials, with numerous waste types currently destined for landfills offering potential for repurposing. This study examines the replacement of natural sand with crushed waste glass and using pond ash as a supplementary cementitious material in mortar, with a particular focus on mitigating alkali-silica reaction (ASR) and assessing compressive strength. Fly ash, widely recognised for its ASR suppression capabilities, is becoming less available due to the decline in coal-fired power generation, necessitating the exploration of pond ash as a viable alternative. However, given the prolonged storage of pond ash in repositories, its direct substitution for fly ash necessitates thorough investigation. Hence, microstructural and chemical analyses are conducted to investigate the underlying reaction mechanisms. The strength results show that glass can replace natural sand with minimal impact on compressive strength up to 60 %, beyond which strength decreases by 11 % at 100 % glass. However, the ASR expansion results indicate that using more than 20 % glass could lead to long-term detrimental effects. Nevertheless, pond ash effectively mitigates ASR, keeping expansions below 0.1 % at a 10 % OPC replacement, although it performs slightly less efficiently than fly ash. At 20 % replacement, pond ash performs similarly to fly ash. Pond ash outperforms fly ash in 28-day strength up to a 20 % OPC replacement and shows better strength development. The optimal balance between ASR mitigation and compressive strength is achieved with 20 % pond ash, allowing for higher glass utilisation without increasing the risk of ASR. • Up to 20 % river sand replacement by waste glass is safe for OPC mortar. • Pond ash is proven to mitigate ASR in mortar with waste glass. • Up to 60 % glass inclusion marginally impacts strength; 100 % reduces it by 11 %. • Pond ash demonstrates superior strength development compared to fly ash. • Optimal performance achieved with 20 % pond ash, maintaining mortar integrity.