Mechanical Properties of Eggshell Filled Non-Post-Cured and Post-Cured GFRP Composites: A Comparative Study

Eggshells, typically discarded as bio-waste in landfills, offer a valuable source of calcium carbonate. Incorporating these shells into polymer composites effectively reduces landfill waste and substitutes inorganic calcium carbonate. The established fact that adding eggshell as a bio-filler enhances the mechanical properties of GFRP composites prompts further investigation, considering variables like reinforcement-material combination, fabrication technique, and curing process. This study aims to assess the impact of different eggshell bio-filler variants on the mechanical properties of glass fiber/polyester composite, also exploring the effects of post-curing. Waste eggshells were processed into uncarbonised and carbonised fillers, which were further mixedto create a hybrid eggshell filler. Three eggshell-filled composite variants and one unfilled variant were fabricated and naturally cured. Another set underwent post-curing after 24 hours of natural curing. Tensile and flexural tests according to their respective ASTM standards were conducted on both non-post-cured and post-cured composites. Results revealed higher strengths in filled composites compared to unfilled ones in both cases. Post-curing enhanced tensile and flexural strengths for all variants. The results of the tensile test indicated that post-curing improved the tensile strength of unfilled composites by 9%, uncarbonised eggshell filled composites by 11% and both carbonised eggshell filled and hybrid eggshell filled composites by 13%. A similartrend was observed with flexural tests. The flexural strength of post-cured unfilled composites improved by 8%, uncarbonised eggshell filled composites by 12%, carbonised eggshell filled composites by 14%, and hybrid eggshell filled composites by 12%. Microscopic analysis highlighted improved crack arrests and reduced propagation in post-cured composites. In conclusion, this study underscores the benefits of post-curing in enhancing the mechanical properties of glass fiber/polyester composites.