Effect of nano-silica@ chitosan phosphate ester on the mechanical properties and water resistance of magnesium oxychloride cement

Nano-silica is used in various composite materials as a kind of filler with good performance. In this study, hydrogen peroxide was used to repair and activate the hydroxyl group on the surface of nano-silica, and chitosan phosphate ester was loaded onto the surface of nano-silica through intermolecular dehydration to prepare nano-silica@ chitosan phosphate ester, and nano-silica@ chitosan phosphate ester was added to the magnesium oxychloride cement for water resistance modification. The results showed that the addition of nano-silica@ chitosan phosphate ester increased the compressive strength of magnesium oxychloride cement at different ages, and the compressive strength of the modified magnesium oxychloride cement at 7 days and 28 days were 116 MPa and 127 MPa, respectively, which increased by 11.5% and 5.8% compared with the unmodified samples. The compressive strength of the modified magnesium oxychloride cement reached 102 MPa after 28 days of water immersion, which was 8.3% higher than that of the phosphoric acid modified sample under the same water immersion duration. At the same time, it was found that nano-silica@ chitosan phosphate ester can increase the fluidity of magnesium oxychloride cement slurry, accelerate the hydration reaction rate and refine the pores.