Mechanical Properties, Microstructure, and Mechanism of Nanosilica-Modified Low-Carbon Magnesium Silicate Hydrate Cement

The slow formation of magnesium silicate hydrate (M-S-H) results in insufficient early strength of M-S-H cement, restricting its wide application. In this study, nanosilica (NS) was applied to modify the performance of M-S-H cement. The influence of NS on the mechanical performance and microstructure was investigated through compressive strength measurements, X-ray diffraction (XRD), derivative thermogravimetry (TG-DTG), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and Mercury intrusion porosimetry (MIP). Subsequently, the hydration mechanism of the M-S-H cement was illustrated after adding NS. The results showed that NS could effectively improve the early strength of M-S-H cement. The compressive strength after 3 days of reaction increased by 59.8%, 130.7%, and 25.7% for 1.5%, 3.0%, and 4.5% NS addition, respectively. After curing for 28 days, the addition of 1.5% NS resulted in a 25.7% increase in compressive strength, whereas the enhancements for samples with 3.0% and 4.5% NS were minimal. NS quickly dissolved to form HSiO43-, H2SiO42-, and H3SiO4-, accelerating the formation of M-S-H and resulting in a higher early compressive strength of the sample. In this study, the novel concept of the addition of NS to M-S-H cement was proposed, which has significant value for the wider application of M-S-H cement in civil engineering.