Eggshell-Derived Additives in Clay Bodies for Sustainable Decorative Ceramic Tiles

Abstract

Nigeria generates about millions of tons of eggshell bio-waste annually, most of which is discarded by informal food vendors, bakeries, and households, creating a significant environmental burden. This study explores the use of eggshell powder composed of roughly 94% calcium carbonate as a sustainable additive in clay bodies for ceramic tile production. The chemical basis lies in the decomposition of calcium carbonate during firing, which releases CO₂ and forms calcium oxide. This promotes liquid phase sintering, densification, and new mineral phases that enhance mechanical strength and surface quality. Collected eggshells were processed into fine (75 micrometres) and coarse (150 to 300 micrometres) fractions, incorporated into clay at 0–20 weight (wt%), and fired at 900°C, 1000°C, and 1100°C. Tiles were tested for modulus of rupture, porosity, shrinkage, water absorption, and surface finish. Results showed that fine eggshell powder at 10 wt% fired at 1100°C yielded the best performance, with an 18% increase in flexural strength and the lowest porosity (3.2%). Porosity decreased with higher firing temperatures, while shrinkage increased with both temperature and eggshell content. Fine fractions improved surface smoothness at ≥1000°C, whereas coarse fractions at 15–20 wt% caused blistering and high porosity due to localised CO₂ release. Overall, the study demonstrates that controlled incorporation of eggshell powder, optimising particle size, proportion, and firing temperature, offers a technically viable, low-cost, and eco-friendly route for ceramic tile production in Nigeria. This approach provides a replicable model for valorizing food industry bio-waste within the domestic ceramics sector.