Phase modification of coral waste and its performance in cement-based materials: Rheology, hydration, and interface strength

This research endeavors to enhance the performance of coral waste in cement-based materials through heat treatment. The phase transformations of coral powder (CP) were analyzed using X-ray diffraction (XRD) and thermogravimetric analysis (TGA). The surface properties of CP and heat-treated coral powder (HTCP) were evaluated using scanning electron microscopy (SEM) and zeta potential tests. The effect of HTCP on the rheology of cement paste was examined, and the surface hydration morphology was analyzed through SEM and diffuse reflectance Fourier trans-form infrared spectroscopy (DR-FTIR). Furthermore, the compressive strength and interface strength of cement paste were assessed. The result showed that aragonite-type CaCO3 of CP is converted to calcite-type CaCO3 by 450 degrees C. HTCP demonstrates stronger adsorption of Ca2+ ions compared to CP, while the adsorption of SO42  ions is weaker. The rectangular sublattice structure of HTCP, composed of calcium and carbonate ions, enhances the adsorption of Ca2+. In contrast, the CP surface, where the Ca2+ layer is positioned between two parallel layers of carbonate ions, favors the adsorption of SO42  . The smoother angle of HTCP creates a "ball bearing" effect that reduces the detrimental impact of smaller particles on flowability, and the higher zeta potential of HTCP particles potentially leads to stronger electrostatic repulsion, improving fluidity. The strong adsorption of Ca2+ ions by HTCP stimulates the nucleation and growth of C-S-H, and the Ca2+ ions adsorbed on the HTCP surface are bonded to C-S-H through similar ionic covalent bonds, resulting in improved adhesion between HTCP and hydrates.