Performance and RSM-based optimization of eco-friendly concrete incorporating seashell powder and bamboo chips

The depletion of natural fine and coarse aggregates due to rapid urbanization poses a significant threat to environmental sustainability. This study explores the performance of eco-friendly concrete incorporating seashell powder (fine aggregate) and treated bamboo chips (coarse aggregate) at replacement levels of 0%, 10%, 20%, and 30% by volume. A total of 111 cylindrical and 12 prism beam specimens were tested in a two-stage experimental program. In Stage I, 18 mix ratios were evaluated based on 28-day compressive strength, identifying the optimal combination (20% seashell powder + 10% bamboo chips, labelled S2B1). In addition to experimental work, Response Surface Methodology (RSM) was employed to statistically optimize replacement levels, with the cubic model predicting 21.6% seashell powder and 0.2% bamboo chips as the mathematical optimum (desirability = 1.0), thereby validating the experimental choice of S2B1 as the practical optimum mix. In Stage II, S2B1 was assessed for compressive strength, split tensile strength, flexural strength, modulus of elasticity, stress–strain response, mass loss, and toughness at 28 and 90 days under ambient and elevated temperatures (200°C, 400°C, 600°C). S2B1 achieved 25.37 MPa compressive strength at 90 days, only 11.9% lower than the control, while also demonstrating improved toughness, ductility, and thermal resilience after extended curing. The synergistic use of these sustainable materials offers a promising alternative for normal-strength concrete applications, with the added advantage of statistical optimization to support experimental findings.