The Effect of Mg2+on the Solidification of Chloride Ions in Portland Cement Paste

Abstract

 In order to investigate the mechanism of the effect of Mg2+ on the solidification of chloride ions in hardened Portland cement slurry, a NaCl-MgCl2 composite solution was used to soak and corrode the hardened Portland cement slurry. Under the condition of fixed total chloride ion concentration of 0.6mol/L, the effects of Mg2+ concentration (0.1mol/L, 0.2mol/L, 0.3mol/L) and soaking time in environmental solutions on Friedel salt production, leaching Ca2+ ion concentration, and leaching of hardened Portland cement were studied The influence law of pH value and other properties in erosive environments. The results showed that in the early stage of immersion erosion, Mg2+ had little effect on the rate of pH increase of the erosion solution; After the pH value of the solution stabilizes, the final pH value of the solution decreases with the increase of Mg2+ concentration; As the concentration of Mg2+ in the erosion solution increases, Mg2+ promotes the dissolution of hydration product Ca(OH)2 and the dissolution of Ca2+, while generating Mg(OH)2 precipitates, resulting in a decrease in solution alkalinity and an increase in the amount of chloride ions solidified; When the pH of the solution exceeds 12.1, a lower pH value will promote the formation of Friedel salts; When the pH of the solution is less than 12.1, higher concentrations of Mg2+ cause Friedel salt to decompose.