Properties of Portland cement paste blended with coral sand powder

This study presents the influence of coral sand powder (CSP) on the hydration and mechanical behaviours of Portland cement paste at the curing ages from 1 day to 90 days. The early hydration kinetics of Portland cement incorporated with CSP is studied by isothermal calorimetry test. The hydrates and pore structures of cement paste are determined by X-ray diffraction (XRD) and mercury intrusion porosimetry (MIP), respectively. Experimental results show that CSP can promote acceleration period to end in advance. XRD results imply that CSP can react with tricalcium aluminate (C ₃ A) to form monocarbonate (Mc) and hemicarbonate (Hc), which can suppress the conversion of Al-phase products, viz. from AFt to AFm. From the MIP results, the addition of CSP can refine the pore structure of Portland cement paste at long-term curing age, although negative effect of CSP on the total porosity can be observed. Low replacement level of CSP (5 wt%) improves the compressive strength of cement mortar at ages from 1 day to 7 days. However, from 28 days to 90 days, the addition of CSP decreases the strength of cement mortar regardless of replacement levels.