Physico-mechanical performance of lightweight geopolymer foam aggregates developed by geopolymerization through microwave-oven irradiations

Climatic change and global warming are pushing researchers to develop waste-based alternatives to cement and conventional concrete, which would have low embodied energy and operational energy due to better insulation properties. In this context, the current study presents the production of ultra-lightweight geopolymer foam aggregate utilizing coal fly ash. Fly ash was activated by two alkaline activators, sodium hydroxide (NaOH) and sodium silicate (Na₂SiO₃), and Na₂SiO₃ performed as foaming agents as well. Sodium bicarbonate (NaHCO₃) was also used as an additive for geopolymer hardening and early strength gain. A novel curing method, microwave-oven curing, was practiced as an alternative to conventional energy and time-intensive curing techniques to promote rapid strength development and sustainability of materials and technology. The physicomechanical performance (morphology, expansion, density, specific gravity, water absorption, strength against compression, and impact loading) of manufactured aggregates was examined for pertinent use to formulate ultra-lightweight foam concrete, and the properties were also compared with natural as well as synthetic lightweight aggregate. Results indicated that manufactured aggregates experienced physicomechanical properties that would be suitable for designing lightweight concrete both for structural and insulation purposes. Satisfactory results of experimentation also confirmed the potential of microwave-oven curing to replace conventional curing techniques to realize economical, energy-efficient, and eco-efficient manufacturing of artificial aggregate.