The role of phosphoric acid in improving the strength of magnesium oxychloride cement pastes with large molar ratios of H2O/MgCl2

Large H2O/MgCl2 molar ratio is good to the soundness of magnesium oxychloride cement (MOC), but detrimental to its strength development. In this paper, the addition of H3PO4 was used to prepare MOC with high H2O/MgCl2 molar ratio (>= 20) and desirable strength development. It was revealed by X-ray diffraction (XRD) and scanning electronic microscopy (SEM) that the primary hydrate of MOC with high H2O/MgCl2 molar ratios was Mg(OH)(2), and the primary hydrate in MOC became 5MgO center dot MgCl2 center dot 8H(2)O (phase 5) in the presence of small amount of H3PO4. The reaction type of MgO with MgCl2 and the formation conditions of phase 5 of MOC with high H2O/MgCl2 molar ratios were both modified by H3PO4.