Valorization of eggshell biowaste in cementitious composites: Mechanical properties and sustainable potential of eggshell powder-modified mortar

This study investigates the use of eggshell powder (ESP) as a partial replacement for cement in mortar, evaluating its effects on mechanical performance, physical properties, setting behavior, and environmental impact. Mortars containing 0–30% ESP by weight of cement were prepared and tested in compression and bending, while density, water absorption, and setting time were also assessed. Microstructural analyses were conducted to interpret the observed mechanical behavior. The results show that mortar performance is optimal at ESP substitution levels of 5–10%. Specifically, the 10% ESP mixture reached a compressive strength of 37.29 MPa (13.97% above control), an elastic modulus of 29.95 GPa, and a flexural strength of 7.74 MPa. In addition, ESP10 reduced the 28-day water absorption from 2.41% to 2.18% and extended the final setting time from 195 to 240 min without degrading mechanical performance. Under the study-specific conservative ESP-processing inventory and absolute volume yield, the 10% ESP mixture increased embodied carbon by 19.77% per cubic meter and increased embodied energy by 13.06% relative to the control mortar. These findings demonstrate that ESP10 provides a favorable measured balance between mechanical performance, physical properties, setting behavior, and normalized environmental efficiency among the investigated mixtures.