High-strength and low-absorption geopolymer artificial aggregates produced under heat, autoclave, and heat-solution curing

Countries like Bangladesh face a shortage of natural aggregate resources, necessitating the development of sustainable alternatives. This study explores the production of durable artificial aggregates using three waste materials: Coal-based Fly Ash (CFA), Medical Waste Incineration Ash (MWIA), and Sewage Sludge Ash (SSA). To address limitations of traditional crushing techniques, a novel heat-solution curing method is developed and compared with heat curing and autoclave curing approaches. Sixteen combinations of cubic geopolymer pastes were prepared and cured for 28 days, with eight selected based on compressive strength for further analysis. The physical and mechanical properties of the aggregates were evaluated through specific gravity, water absorption, aggregate impact value, and soundness tests. Advanced characterization techniques, including Scanning Electron Microscopy (SEM), Energy-dispersive X-ray Spectroscopy (EDS), and X-ray Diffraction (XRD), were employed to understand the microstructural properties. Among the samples, the heat-solution cured C100 (CFA: SSA: MWIA = 100:0:0) demonstrates the lowest water absorption of 16.4% and aggregate impact value of 24. The heat-solution cured C80S10M10 (CFA: SSA: MWIA = 80:10:10) exhibits the lowest mass loss of 2.1% after a five-cycle soundness test and satisfactory physical and mechanical properties across all curing methods. XRD analysis identifies crystalline compounds such as quartz, mullite, and calcite, indicating successful geopolymerization. SEM analysis reveals dense, amorphous formations on CFA and SSA particles, confirming effective bonding, while EDS analysis shows a maximum silica-to-alumina (Si/Al) ratio of 2.03 for C80S10M10, correlating with superior mechanical strength. In addition to having substantially lower heavy metal leaching than raw ashes, stabilized C80S10M10 samples satisfy USEPA's LDR requirements under all curing conditions. Life cycle analysis further underscores the environmental benefits of this approach compared to conventional brick aggregates. This study concludes that artificial aggregates produced from CFA, MWIA, and SSA offer a sustainable and eco-friendly alternative to natural aggregates, contributing to waste management and resource conservation.