An experimental and statistical investigation into the optimisation of eco-friendly concrete incorporating agricultural and industrial wastes

This research aims to develop a sustainable concrete matrix incorporating fire clay, rice husk, and fly ash. This study investigates the use of fire clay (FC) as a partial substitute for sand, fly ash (FA), and rice husk (RH) in cement-based concrete mixes to enhance sustainability, reduce costs, and improve mechanical and microstructural properties. Concrete specimens with varying levels FC replacement (0%, 12%, 25%, 36%, and 50%), FA, and RH (0, 4%, 8%, 12%, 16%) were tested for compressive and flexural strength at 3, 7, 14, and 28 days. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to investigate changes in microstructural and phase composition. The results demonstrated a progressive decline in mechanical properties with increased FA, RH, and FC content, primarily due to the dilution effect of FA, RH, and FC particles, which disrupt the cementitious matrix and weaken structural integrity. The control mix had a compressive strength of 29.32 MPa, whereas the mix with 8% FA, 8% RH, and 25% fire clay replacement had a compressive strength of 31.65 MPa, a 2.5% increase with equivalent mechanical properties. After an acid attack, the control mix had decreased hydration products, whereas the FA, RH, and FC replaced mixes had sustained quartz peaks, indicating structural integrity. SEM study showed that FA, RH, and FC enhance the porosity of the cement matrix and micro-cracks after acid exposure, but improve packing density and stability before acid exposure. Furthermore, a two-way statistical analysis of variance (ANOVA) with a p-value of less than 0.001 and R-squared (R²) values ranging from 0.925 to 0.954 demonstrated that the model is statistically significant. By optimising the substitution levels of FA, RH, and FC, the importance of achieving the desired mechanical and microstructural properties while maximising sustainability benefits can be further enhanced. This research advances sustainable construction practices by demonstrating the potential of FA and RH as partial cement substitutes and FC as a fine aggregate substitute. The results facilitate the development of sustainable concrete technology and the implementation of environmentally favourable construction practices.