Impact of Sodium Gluconate Admixture on the Properties of Magnesium Oxysulfate Cement

Magnesium oxysulfate (MOS) cement, a building material, can be considered the result of the hydration reaction between magnesium sulfate, caustic-burned magnesia powder, and water. Despite its desirable properties, such as limited mechanical strength and water resistance, MOS cement can hinder its use in engineering applications. We employed several testing methods to assess the impact of sodium gluconate (SG) addition on the compressive strength, microstructure, moisture resistance, coagulation time, pH profile, micropore parameters, phase composition, and thermal decomposition of MOS cement's hydration products. The addition of sodium gluconate improves the stability of the hydration film surrounding active magnesium oxide in magnesium sulfate. This extension in the setting time of MOS cement is observed. Additionally, it inhibits the creation of magnesium hydroxide while facilitating the formation of numerous needlelike structures corresponding to the 5Mg(OH)2·MgSO4·7H2O (5·1·7 phase). Consequently, the mechanical strength and water resistance of MOS cement are substantially improved compared to the unmodified sample.