From Waste to Resilience: A State-of-the-Art Review on Fly Ash-Based Rubberized Geopolymer Concrete

The construction sector remains heavily dependent on Ordinary Portland Cement (OPC) and natural aggregates worldwide, making it one of the largest contributors to carbon emissions and resource depletion. At the same time, industries still have challenges in properly disposing of fly ash and tires with a minimum useful life, both of which are produced in enormous quantities annually. Fly Ash-Based Rubberized Geopolymer Concrete (FRGC) presents a suitable alternative to replace cement, natural aggregates used in conventional concrete, and reduce carbon footprint by utilizing waste products. A geopolymer binder made from low-calcium fly ash is used in place of OPC in FRGC, and rubber fragments recovered from used tires are used in place of some of the natural aggregates. An extensive review is therefore performed in this study to highlight the research gaps to be addressed in the future and potential challenges in achieving the goal. The present study also examines the effects of rubber size/content, curing regime, silicate-to-hydroxide ratio, and alkaline activator molarity on the mechanical, fresh, and durability characteristics of FRGC. Results from previous studies show that adding rubber by 6% can lower compressive strength by 10–25%. However, it significantly improves ductility, impact resistance, and energy absorption by more than 50%. However, the geopolymer binder lowers the carbon footprint of concrete by 60–80% as compared to OPC and offers great early strength and exceptional durability in harsh settings. This consolidated literature reveals that while the alkaline chemistry of geopolymer binders and the toughness benefits of rubber are individually well studied, their combined influence under elevated curing and fire exposure remains critically underexplored. Furthermore, long-term durability and corrosion studies of FRGC are scarce, and no comprehensive datasets exist for machine learning-based prediction. Addressing these gaps will define the trajectory for future research and standardization.