Layered double hydroxides nanosheets for capturing chloride ions in magnesium oxychloride cement

Abstract

As an alternative inorganic cementitious material, the application of magnesium oxychloride cement (MOC) is often limited due to its poor water resistance, which caused by the migration of Cl- to the surface. In this research, magnesium aluminum layered double hydroxides (Mg2Al-LDH) nanosheets were used to capture the free Cl- in MOC paste taking advantage of the enormous specific surface area of the Mg2Al-LDH nanosheets with ultrathin structure. The Cl- adsorption capacity of Mg2Al-LDH nanosheets in KCl solution was one order of magnitude higher than that of LDH particles prepared traditionally. The scumming of the MOC cube under high humidity was efficiently avoided at the optimum dosage of 2.0% Mg2Al-LDH nanosheets. The compressive strength of the MOC cured under sealed conditions increased by 13–118% over the control sample at various dosages in the range of 0.5–2.0%, and the maximum value of compressive strength was obtained at optimum Mg2Al-LDH dosage of 2.0%. The morphology of MOC under high humidity curing showed that more rod-like hydration products were formed by adding LDH nanosheets into MOC paste. The results demonstrated a suitable dosage of LDH nanosheets not only increased the efficiency of capturing Cl-, but also stimulated the formation of rod-like crystals and enhanced the compressive strength of the MOC cube.