Performance assessment of reclaimed fly ash-slag geopolymers incorporating waste spent garnet and waste foundry sand under different curing regimes.

Fly ash (FA) landfills are overflowing with materials, and unexplored waste streams like waste spent garnet (WSG) and waste foundry sand (WFS) are often dumped in onsite storage spaces, limiting land availability for future use and exacerbating environmental concerns related to waste disposal. Therefore, this research proposes recycling FA to produce reclaimed FA (RFA) as a binder, replacing 40-60 % of ground granulated blast furnace slag (GGBFS) and 30-50 % of river sand (RS) with WSG and WFS to produce geopolymers. The performance of geopolymers was assessed under different curing regimes, including ambient-temperature curing (ATC), ambient-temperature water curing (AWC), high-temperature curing (HTC), and high-temperature water curing (HWC). The results revealed that geopolymers with higher RFA content show similar or better performance than those with high GGBFS content in areas like acid attack resistance, drying shrinkage, and high-temperature resistance, confirming that up to 60 % RFA can be used for commercial applications. Moreover, at least 30 % of WSG and WFS can replace RS in geopolymers for various applications, while up to 50 % replacement is possible with WSG or WFS, provided some performance compromise, particularly in carbonation resistance, is acceptable. Overall, AWC outperformed other curing regimes, highlighting the importance of moisture for adequate performance without the need for high temperatures, unless very high early-age strength is required, thereby offering potential savings in cost and energy. These geopolymers gain strength and durability through the polymerization of GGBFS and RFA, forming calcium- and sodium-rich reaction products; the incorporation of WSG and WFS enhances packing density and reduces porosity, while and water-based curing regimes, such as AWC and HWC, promote greater reaction product formation and improved microstructural development. This research promotes the use of RFA and waste materials in geopolymer production, fostering sustainability by reducing material reliance and environmental impact.