Synergistic effect of coral sand and coral powder on the performance of eco-friendly mortar

Raw materials for concrete are often harder to come by on islands farther inland. Converting coral waste from island construction into aggregates and binders for concrete is an eco-friendly strategy. This study focuses on the utilization of waste coral powder (CP) and coral sand (CS) as substitutes for cement and natural aggregate in the preparation of cement-based materials. The mechanical properties, volume stability, microstructure and environmental benefits were investigated. The results indicate that adding a minimal quantity of CP (10%) to the cement paste enhances the strength in the samples. Meanwhile, adding 10-40% CS effectively improves the mechanical properties of coral-based mortar. The coral-based mortar, with the combined application of 10% CP and 30% CS, has the highest mechanical properties, with its 28-d compressive strength being 28.89% higher than that of the reference group. Furthermore, adding a proper quantity of CP and CS enhances the volume stability of cement-based materials. The nanoscale characterization also reveals that CS incorporation increases the matrix's gel phase content, particularly the ratio of high-density C-S-H and exhibits a more excellent interfacial transition zone (ITZ) performance between CS and the matrix. In addition, the waste coral-based cement components exhibit reduced non-renewable energy consumption and CO2 emissions, facilitating the efficient utilization of waste materials and promoting sustainable development.