Valorization of agricultural and industrial wastes in geopolymer foam concrete, a ternary binder approach using corncob ash, red mud, and fly ash

This study examines the growing need for sustainable and thermally efficient lightweight concretes, specifically through the advancement of geopolymer foam concrete (GFC). This novel material integrates industrial red mud (RM) and agricultural corncob ash (CCA) as partial replacements in a fly ash–based binder. This study aims to investigate the issues associated with foam instability, increased water absorption, and reduced mechanical strength that are commonly observed in waste-derived GFC materials. Six mix formulations (GC1–GC6) were developed by adjusting the CCA content from 0 to 250 kg/m³, and their rheological, thermal, mechanical, electrical, and microstructural properties were assessed. The measurement of compressive strength was conducted at both 3 and 28 days, whereas all additional tests were executed on samples that had been cured for 28 days.The findings indicated that the incorporation of moderate amounts of CCA (100–150 kg/m³) led to improvements in foam stability, enhanced thermal insulation properties, and preserved sufficient structural integrity, with GC3 demonstrating the highest 28-day compressive strength of 2.86 MPa. Excessive CCA (GC6) resulted in unstable pore structures, diminished gel formation, increased water absorption (62.7 %), and the lowest strength recorded (1.45 MPa). The thermal conductivity exhibited a reduction from 0.91 to 0.52 W/m·K, while the electrical resistivity demonstrated an increase from 6.1 to 35.2 Ω·m across the various mixes, suggesting enhanced insulating characteristics as the content of CCA increased. SEM–EDS analysis validated the presence of well-structured geopolymer gels in low-to-moderate CCA mixtures, while revealing disrupted matrices at elevated CCA concentrations.The findings of the study indicate that optimized RM–CCA–FA ternary binders are capable of generating lightweight, low-carbon GFC that exhibits enhanced thermal and electrical properties, thereby supporting the development of sustainable construction materials in accordance with the Sustainable Development Goals 9, 11, 12, and 13.