Influence of the Addition of Eggshell Ash on the Strength of 1:3 Mortars

Abstract This study investigates the effect of incorporating eggshell ash (ESA) into 1:3 mortars and its influence on physical, mechanical, and microstructural properties. Mortars were prepared with 0%, 5%, and 10% ESA additions relative to cement weight. Characterization techniques included XRD, SEM, compressive and flexural strength tests, modulus of elasticity, and porosity analysis. Results demonstrated that 5% ESA enhanced early and 28-day compressive strength (31.34±1.14 MPa), reduced porosity (27.95%), and improved microstructure continuity, indicating nucleation and filler effects. In contrast, 10% ESA promoted excess Ca(OH)2 and ettringite formation, increasing heterogeneity and decreasing performance (26.61±1.80 MPa). XRD confirmed secondary phase formation, and SEM images corroborated matrix densification at optimal dosage. The findings suggest that ESA is a viable, eco-friendly additive, with 5% representing an optimal content that maximizes performance without compromising durability. Excess ESA (>10%) may impair mechanical behavior due to calcium oversaturation and porosity increase, highlighting the need for dosage control.