The effects of heavy calcium powder and slag together as auxiliary cementitious materials on the compressive strength of cementitious sand and the synergistic effects were investigated. The hydration products, microscopic morphology and pore size distribution of cementitious materials were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), heat of hydration method, nuclear magnetic resonance (NMR) technique and mercury intrusion porosity (MIP). The results show that the strength of cement mortar being mixed with heavy calcium powder and slag is higher than that of single slag, and higher than that of pure cement mortar in the later stage. Heavy calcium powder particles become the core of cement hydration product growth, and promote cement hydration, so that the hydration products are tightly bound; heavy calcium powder later has hydration, and reacts with the aluminum phase in slag to generate calcium monocarboaluminate hydrate (Ca₄Al₂O₆·CO₃·11H₂O), which improves the pore size distribution of cement paste and refines the pore size. This is the main reason that heavy calcium powder and slag as an auxiliary cementitious material improve the strength of cement mortar.

Keywords: Heavy calcium powder, Supplementary cementitious material, Porosity, Microstructure.