Exploring the influence of calcinated eggshell powder on lightweight foamed concrete: A comprehensive study on freshness, mechanical strength, thermal characteristics, and transport properties

This research aimed to explore the feasibility of using calcined eggshell powder (CESP) as a substitute for cement in the production of lightweight foamed concrete (LWFC), considering its high calcium content. Ten LWFC mixtures consisting of two densities of 600 kg/m3 and 1200 kg/m3 were produced and tested. Each density comprised mixtures with varying proportions of CESP, ranging from 0% to 20% in increments of 5%. The ES was calcined at 900 °C to convert the CaCO3 into CaO. The fresh, transport, mechanical, microstructural, and thermal properties were investigated. The findings revealed that the slump flow and setting times progressively decreased as the CESP proportion increased. The water absorption, sorptivity and intrinsic air permeability improved steadily as the CESP proportions were increased from 5% to 20%. Additionally, the compressive strength, flexural strength, splitting tensile strength, modulus of elasticity, and drying shrinkage went through an initial increase and then a decrease, and the optimal CESP replacement rate was found to be 15%. The 28-days compressive, flexural and splitting tensile strengths enhancements with 15% CESP replacement were 44.3%, 41.2% and 41.7% and 39.7%, 56.5% and 57.6% for 600 kg/m3 and 1200 kg/m3 densities respectively compared to control mix. Besides, a marginal rise in thermal conductivity and diffusivity was observed as the proportion of CESP increased. Based on the SEM and pore dispersion results, the incorporation of up to 15% CESP into both LWFC densities resulted in an improved microstructure and enhanced pore dispersion, leading to the formation of a greater amount of C–S–H compounds. The findings were substantiated by enhanced mechanical properties, transport characteristics and SEM results.