Study on effects of acidic environment on structure and property of magnesium oxychloride cement

Abstract To reveal the effects of acidic environment on structure and property of magnesium oxychloride cement (MOC), the evolution of macro- and micro-morphologies, phase composition and mechanical property of MOC samples with soaking time in 5 wt.% H₂SO₄ solution were studied by using SEM, XRD, FT-IR and microelectromechanical electrohydraulic servo-pressure testing machine, respectively. The results show that the deterioration of MOC sample under acidic environment is mainly attributed to the consumption of the sample caused by the reaction between H⁺ ions and the substances in sample. The longer the soaking time, the more the sample consumed by H⁺ ions, and the more serious the deterioration of the sample. After dipping in H₂SO₄ media for 12h, the mass loss rate of MOC sample is up to 77.5%, and its volume decreases by nearly 3/4. Meanwhile, the surface morphology of MOC sample is changed from gel and needle rod to granular, and the content of P5, Mg(OH)₂ and MgO reduce, resulting in the compressive strength of MOC samples declining by 92.2%. However, due to the volume effect, H⁺ ions do not invade the inner core of the sample, so that the micro-morphology and phase composition of the inner core are almost unchanged. In short, MOC sample gradually deteriorates under acidic environment through being consumed by H⁺ ions from the outside to the inside.