Effect of nano-silica on properties and microstructures of magnesium phosphate cement

Abstract

The prime concern of this work was to investigate the effects of nano-silica on the properties of magnesium phosphate cement (MPC), and were analyzed in terms of the fresh property, mechanical performance, microstructure, and hydration products. The results showed that successive additions of nano-silica from 0% to 6% caused a decreased fluidity and a shortened setting time of the fresh paste. The mechanical property of the hardened sample was enhanced by adding nano-silica, and the group containing 4% nano-silica (NS4) yielded the 28-day compressive strength of 95.3 MPa, which was the highest in the research. For NS4 with a fluidity of 270 mm and a setting time near 20 min, it met the requirement of the rapid-repair material. The microstructure and hydration product analyses of the hardened paste were conducted by X-ray diffraction (XRD), scanning electron microscopy-energy dispersive spectrometer (SEM-EDS), Fourier Transform Infrared Spectroscopy (FTIR), and thermal analysis (TGA-DTG). The ultra-fine nanomaterial had an excellent pore-filling effect in MPC, which compacted the microstructure. Nano-silica was highly reactive and could be involved in the acid-based reaction of MPC. The investigation on the hydration mechanism of magnesium-silica system confirmed that the vast heat released during the hardening period promoted the formation of magnesium silicate hydrates (M-S-H) and brucite (Mg(OH)2).