Particle Size–Controlled Sintering of Stoneware Ceramics via Uncalcined Green Mussel Shell Waste for Reduced-Temperature Stoneware Production

The demand for sustainable ceramic processing has stimulated interest in waste-derived fluxing materials that can reduce firing requirements. This study investigates the direct incorporation of uncalcined green mussel shell powder into stoneware bodies, thereby eliminating an additional precalcination step. Three shell particle-size fractions were incorporated at 10–20 wt% and fired at 800–1250 °C. Rietveld refinement showed that all fractions were aragonite-rich, indicating that differences in thermal behavior were primarily associated with particle size rather than CaCO 3 polymorph composition. Medium-sized shell particles at 10 wt% (MGS10) exhibited the most favorable processing behavior, with concentrated carbonate decomposition occurring over approximately 650–800 °C, allowing CO 2 to evacuate before advanced matrix vitrification. Shell-derived Ca 2+ subsequently acted as a network modifier within the aluminosilicate glass, promoting liquid-phase sintering and densification at 1150 °C, while further reaction at 1250 °C resulted in anorthite crystallization. MGS10 achieved a bulk density of approximately 2.38 g cm -3 and a water absorption value of approximately 0.8% at 1250 °C, comparable to that of the unmodified stoneware body, while maintaining structural integrity at 1150 °C. These results demonstrate that particle-size control is critical for integrating uncalcined biogenic CaCO 3 into stoneware and provides a practical route for shell-waste valorization and reduced-temperature ceramic processing.