Performance optimisation of biomass ash and rice husk ash-based geopolymer concrete using response surface methodology for enhanced strength and durability

This study optimises and evaluates the performance of geopolymer concrete (GPC) produced using biomass ash (BA) and rice husk ash (RHA) sourced from Punjab, India. A Box–Behnken design within the Response Surface Methodology (RSM) framework examined four key variables – BA content (40–60%), RHA content (40–60%), alkaline-to-binder ratio (0.35–0.45) and NaOH molarity (8–12 M) – to assess their effects on mechanical and durability properties. Twenty-nine GPC mixes were tested for strength, permeability and chemical resistance. Statistical analysis identified NaOH molarity as the most influential factor, followed by the A/B ratio and ash proportions. The optimal mix (B50R50A35M12) achieved 29.5 MPa compressive strength, 3.55 MPa split tensile strength, low permeability (5.46% water absorption, 0.057 mm/min0·5 sorptivity, 15.15% porosity, 2430 C RCPT) and enhanced acid (5.69% weight loss) and sulphate resistance (6.51% strength loss), outperforming M30-grade OPC concrete. Microstructural analysis (SEM, XRD, FTIR and TGA) confirmed a dense, well-polymerised sodium aluminosilicate hydrate (N–A–S–H) gel. Cost and life-cycle analyses revealed 25–30% lower cost and up to 70% reduced CO2 emissions. Overall, BA–RHA-based GPC offers a sustainable, high-performance and low-carbon alternative for durable structural applications.