Valorization of recycled concrete powder, clay brick powder, and volcanic pumice powder in sustainable geopolymer concrete

The use of recycled powder as a binder in geopolymer concrete (GPC) represents a promising approach to reducing construction waste and promoting the production of sustainable materials. This study examines the impact of recycled concrete powder (RCP), clay brick powder (CBP), and volcanic pumice powder (VPP) on the mechanical, durability, and thermal properties of GPC with fly ash and slag under water curing. Key mechanical properties, including compressive strength (CS), splitting tensile strength, and flexural strength, were evaluated, while durability was assessed through water absorption, water penetration, and resistance to sulfate and acid attacks. The thermal performance was tested by exposing the samples to elevated temperatures of 200 °C, 400 °C, and 600 °C. Results demonstrated that incorporating 25% RCP enhanced CS by 14.88% at 28 days compared to the control mixture, although higher replacement levels (50% and 75%) led to reduced CS due to increased porosity. Similarly, CBP at 25% substitution resulted in a 21.12% increase in CS, with declines observed at higher replacement levels. Conversely, VPP at 25% substitution decreased CS by 8.68% at 28 days, with further significant reductions at higher levels due to its high porosity. Sulfate resistance testing in a 5% MgSO₄ solution showed minimal mass loss for CBP mixtures (0.3–1.2%) and moderate CS reductions (5.7–29.6%). RCP mixtures exhibited low mass loss (0.3–1.7%) and CS reductions (8.7–15.8%), while VPP mixtures experienced the highest mass losses (1.36–3.4%) and CS reductions (20.5–31.3%). SEM analysis revealed that RCP and CBP mixtures exhibited denser microstructures, which contributed to their enhanced durability and thermal stability. Generally, optimizing the replacement levels of RCP, CBP, and VPP improves the durability, pore structure, and mechanical performance of GPC. Among the materials, CBP demonstrated superior resistance in acidic environments, while RCP excelled in thermal stability, demonstrating their potential for producing sustainable and durable geopolymer concrete.