Experimental investigation on the strength and durability behaviour of high-strength nano silica concrete with eggshell powder

This study investigates the combined effects of treated eggshell powder (ESP) and nano silica (NS) on the fresh, mechanical, durability, sustainability, and economic performance of M60 HSC. A constant replacement of 5% cement with ESP was adopted, while NS was incorporated at 0, 0.5, 1.0, 1.5, and 2.0% by mass of the total binder. Fresh concrete properties were evaluated through slump tests, whereas hardened concrete performance was assessed using compressive strength, split tensile strength, flexural strength, water absorption, and water permeability tests. The results demonstrated that increasing NS content reduced workability because of its high specific surface area. However, the mixture containing 5% ESP and 1.5% NS exhibited the optimum performance, achieving compressive, split tensile, and flexural strengths of 71.6 MPa, 5.6 MPa, and 8.2 MPa, respectively. The optimum mixture also recorded the lowest water absorption (2.6%) and water permeability coefficient (1.6 × 10⁻¹¹ m/s), indicating improved pore refinement and enhanced durability. Sustainability assessment revealed a 6.5% reduction in Portland cement consumption, corresponding to an estimated reduction of 31.76 kg CO₂/m³ of concrete. Economic analysis showed that although the optimum mixture increased the initial material cost by 27.35%, the substantial improvements in mechanical performance and durability are expected to enhance long-term service life and reduce maintenance requirements. Overall, the synergistic incorporation of 5% ESP and 1.5% NS provides an effective approach for producing sustainable high-strength concrete with improved structural performance, enhanced durability, and reduced environmental impact.