Effect of sodium sulfate and gypsum on performances of expansive grouting material with aluminum as expansion agent

Abstract

In order to compensate the shrinkage of cement-based grout after hardening, volume expansion was produced by adding sodium sulfate or gypsum into aluminum powder blended grouting materials to enhance the expansion and strength. It was found that the addition of sodium sulfate or gypsum not only improved the expansive performances, but also enhanced the strength of specimens by increasing the amount of hydration products. When the water-cement ratio was fixed at 0.40 and aluminum powder content was at 0.5 wt‰, with the increase of sodium sulfate content, the volume expansion was accelerated, and the expansion rate gradually increased. The compressive strengths at 3d and 28d were the best at 0.5 wt%, especially the 28d compressive strength was increased by 14.7%. With the increase of gypsum content, the starting time of expansion was delayed, but the expansion rate was increased. The 3d compressive strength first increased and then decreased, and the 28d compressive strength was increased by 59.8% with 4 wt% gypsum. The mechanisms were that sodium sulfate increased the pH value of the slurry, while gypsum promoted the formation of ettringite (AFt), which caused different effects on the gas generation characteristics of aluminum powder. The results indicated that the optimum contents of sodium sulfate and gypsum in this aluminum powder blended grouting material were 0.5 wt% and 4 wt%, respectively, which had highest compressive strength and good expansion behaviors.