Influence of H2O/MgCl2 molar ratio on strength properties of the magnesium oxychloride cement solidified soft clay and its associated mechanisms

•Eco-friendly magnesium oxychloride cement (MOC) is used to solidify soft clay, and the optimal H2O/MgCl2 molar ratio ranges of MOC-solidified soft clay is suggested.•The influence of the H2O/MgCl2 molar ratio on the mechanical properties of MOC-solidified soft clay is dependent on MgO/MgCl2 molar ratio.•The UCS of MOC-solidified soft clay is higher than that of Portland cement-solidified soft clay under appropriate H2O/MgCl2 and MgO/MgCl2 molar ratios.•The relationship between elastic modulus and UCS of MOC-solidified soft clay is similar to that of solidified soil with traditional methods.•Phase 5, phase 3 and Mg(OH)2 are identified as dominant products of MOC-solidified soft clay. The solidifying soft soils with eco-friendly magnesium oxychloride cement (MOC) have gained much attention due to increasing environmental protection concerns. In this paper, a parametric study has been conducted to investigate the influence of H2O/MgCl2 molar ratio on the mechanical properties of MOC-solidified soft clay at different MgO/MgCl2 molar ratios and curing times by performing unconfined compressive strength (UCS) tests. The microstructure and pH were studied to the inherent mechanisms by scanning electron microscopy (SEM), X-ray diffraction (XRD), and acid-base tests. The results indicate that the influence of the H2O/MgCl2 molar ratio on the mechanical properties of solidified soft clay is dependent on MgO/MgCl2 molar ratio. The optimal H2O/MgCl2 molar ratio was found as 15–20 when MgO/MgCl2 molar ratio was 3:1 – 5:1, while it was 29 – 41 when MgO/MgCl2 molar ratios were 6:1 and 7:1. The main hydration products of MOC-solidified soft clay with MgO/MgCl2 molar ratio of 3:1 – 4:1 were 5 Mg(OH)2·MgCl2·8H2O (phase 5) and 3 Mg(OH)2·MgCl2·8H2O (phase 3), whereas phase 5 and Mg(OH)2 were mainly produced when MgO/MgCl2 molar ratio was 5:1–7:1. The UCS increases and then exhibits a decreasing trend with the curing time due to the gradual transformation of phase 5 into phase 3 and Mg(OH)2. The influence of curing time is dependent on H2O/MgCl2 molar ratio. The pH value first increases and then decreases with the H2O/MgCl2 and MgO/MgCl2 molar ratios, while it decreases with the curing time. The decreasing pH value results in the instability of the hydration products and reduced UCS of MOC-solidified soft clay.