Comparative study of the effects of magnesium aluminum silicate and bentonite clay on the properties of magnesium phosphate cement-based grouting material

Abstract

In this paper, mineral admixtures of magnesium aluminum silicate (MAS) and bentonite clay (BC) were added to magnesium phosphate cement-based grouting material (MPCG) to improve its poor water resistance and large shrinkage deformation of the matrix, and the effects of MAS and BC on the properties of fresh slurry, compressive strength, volume stability and microstructure of MPCG were comparatively studied. The research results showed that MAS and BC reduced the shrinkage deformation of MPCG, increased MPCG’s density, and decreased porosity. After curing for 28 d, the compressive strength and water resistance of MPCG were improved by adding 2.0 wt% of MAS or BC, and the compressive strength and softening coefficient were 13.9 ± 0.4 MPa and 0.87 (MAS), 12.2 ± 0.7 MPa and 0.84 (BC), respectively, which were all higher than the control group. The hydration heat and phase composition showed that the addition of MAS or BC reduced the cumulative heat of MPCG, but no new crystal phase was formed. The addition of MAS increased the formation of K-struvite (MgKPO4·6H2O), while BC reduced the formation of K-struvite. Therefore, MAS and BC could be used as admixtures of MPCG to improve its workability.