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

Abstract Large H 2 O/MgCl 2 molar ratio is good to the soundness of magnesium oxychloride cement (MOC), but detrimental to its strength development. In this paper, the addition of H 3 PO 4 was used to prepare MOC with high H 2 O/MgCl 2 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 H 2 O/MgCl 2 molar ratios was Mg(OH) 2, and the primary hydrate in MOC became 5MgO·MgCl 2 ·8H 2 O (phase 5) in the presence of small amount of H 3 PO 4. The reaction type of MgO with MgCl 2 and the formation conditions of phase 5 of MOC with high H 2 O/MgCl 2 molar ratios were both modified by H 3 PO 4. [ABSTRACT FROM AUTHOR]