Upcycling reclaimed fly ash and waste tire crumb rubber through geopolymerization: Synthesis, characterization, and...

The declining availability of high-quality fly ash (FA) poses a challenge to sustainable construction and reducing cement-related environmental impacts. Moreover, non-biodegradable wastes such as end-of-life tires present significant challenges due to their large volume, complex structure, and potential to release toxic chemicals, making recycling difficult. Therefore, this study investigates the potential of leveraging geopolymer technology to upcycle reclaimed FA (RFA) (recycled landfilled FA) and waste tire crumb rubber (WCR). RFA and ground granulated blast furnace slag (GGBFS) were used as binders, with river sand (RS) and WCR (30 % and 50 % replacements) as fine aggregates under various curing regimes, including ambient-temperature curing (ATC), ambient-temperature water curing (AWC), high-temperature curing (HTC), and high-temperature water curing (HWC). The performance of these geopolymers were evaluated based on flow diameter, mechanical performance, transport properties, and microstructural characteristics. The results revealed that incorporating 60 % RFA and 30 % WCR in geopolymers provided adequate fluidity and mechanical performance suitable for various construction applications. While geopolymers containing RS under ATC and HTC achieved sufficient strength, replacing RS with WCR led to a significant reduction in mechanical performance. In contrast, all geopolymers under AWC and HWC demonstrated both adequate strength and resistance to environmental agents. Additionally, increasing the RFA content slightly reduced production costs, whereas incorporating WCR led to a cost increase. These findings demonstrate that RFA and WCR can be used without compromising performance standards, promoting sustainable construction and effective waste management.