Impact of Cl- on the performance of magnesium oxysulfate (MOS) cement

As magnesium oxysulfate (MOS) cement finds more applications in the engineering field, the influence of Cl- on the mechanical properties of MOS cement has gained more attention. In this paper, MgCl2<middle dot>6 H2O served as the source of Cl- to investigate its influence on the evolving properties of MOS cement. The results showed that MgCl2<middle dot>6 H2O extended the formation time of the 5Mg(OH)(2)<middle dot>MgSO4<middle dot>7 H2O phase, reduced the dispersion of the MOS cement system, and decreased the crystalline size of the 5Mg(OH)(2)<middle dot>MgSO4<middle dot>7 H2O phase (200) crystal plane. The addition of MgCl2<middle dot>6 H2O had a positive effect on improving flexural strength and increasing the content of gel. During the curing process, the presence of Cl- facilitated the dissolution and recrystallization of Mg(OH)(2), altering its growth tendency and promoting the formation of hexagonal crystal Mg(OH)(2). During soaking in water, the increased content of MgCl2<middle dot>6 H2O led to a decrease in the softening coefficient due to the dissolution of excess MgCl2. The structure of the 5Mg(OH)(2)<middle dot>MgSO4<middle dot>7 H2O phase underwent changes as Cl- entered the crystal interior, leading to an increase in the d-spacing of the 5Mg(OH)(2)<middle dot>MgSO4<middle dot>7 H2O phase at the (222) crystal plane. The introduction of Cl- endowed the 5Mg(OH)(2)<middle dot>MgSO4<middle dot>7 H2O phase with the potential to transform into 5Mg(OH)(2)<middle dot>MgCl2<middle dot>8 H2O. Following immersion in water, the modified structure of the 5Mg(OH)(2)<middle dot>MgSO4<middle dot>7 H2O phase retained its relative integrity, resulting in a higher softening coefficient of 0.73 after a 90-day soaking period, attributed to the proper introduction of Cl-.