Microstructural and micro-mechanical characteristics of cement paste incorporating cuttlebone powder

Introduction. Marine bio-waste provides a sustainable calcium-rich resource for cementitious materials, but its role in hydration control remains limited. Cuttlebone powder (CBP) is a marine bio-calcium with a porous hierarchical structure, and it forms a nanostructured calcium carbonate system. This system influences phase evolution and structure–property relationships in cement paste. This study evaluates its effects on phase composition, Ca/Si balance, microstructure, and structure–property relationships. Materials and Methods. The study prepares plain and CBP-modified cement paste. CBP replaces cement at 10–50% by weight. All mixtures use a constant w/b ratio of 0.5 and cure for 28 days. TGA evaluates phase composition, EDS determines Ca/Si ratio, SEM and mapping examine microstructure, and Vickers hardness measures micro-mechanical properties. Results. CBP modifies the phase composition of cement paste. Calcium hydroxide decreases from 18.68% to 13.13%, while calcium carbonate increases from 2.80% to 15.05%. The Ca/Si ratio increases and indicates a Ca-rich system. The microstructure becomes heterogeneous, and Ca distribution becomes more localized, while Si remains relatively stable. Micro-mechanical properties increase up to CBP40 and decrease at higher replacement levels. Discussion. CBP influences hydration through its porous hierarchical structure and calcium carbonate composition. This structure controls ion distribution and phase development and governs Ca/Si balance and microstructural evolution. The results establish a structure–property relationship and define the micro-mechanical response. Conclusion. CBP acts as a nanostructured calcium carbonate and alters phase composition, Ca/Si balance, and microstructure. This modification improves micro-mechanical performance at moderate replacement levels but reduces matrix continuity at higher levels.