Physicochemical properties of MgO-silica fume cementitious materials exposed to high temperatures

In this paper, MgO and silica fume (SF) are used to prepare MgO-SF cementitious materials, physicochemical properties of MgO-SF materials at room temperature (RT), 100 & DEG;C, 200 & DEG;C, 300 & DEG;C, 400 & DEG;C, 600 & DEG;C and 800 & DEG;C are studied. By means of X-ray diffraction (XRD), fourier transform infrared spectroscopy (FT-IR), nuclear magnetic resonance (Si-29 MAS-NMR), mercury intrusion porosimetry (MIP) and scanning electron microscopy-energy spectrometer (SEM-EDS), the changes of cementitious phase are explored to support the strength change results. The research results show that after a high temperature of 800 & DEG;C, the residual compressive strength of MgO-SF mortars is between 43.19% and 66.18%, showing excellent high-temperature resistance. XRD, FT-IR and SEM-EDS test results show that M-S-H gel has stronger thermal stability than brucite. The Si-29 MAS-NMR results show that the M-S-H gels at the Q(1) and Q(2) sites turned to the Q(3) site under the action of high-temperature, showing stronger stability. Under the action of high temperature, the presence of MgO-SF undergoes rehydration and M-S-H gel partially decomposes. When the temperature exceeds 400 & DEG;C, the brucite loses water and decomposes, the M-S-H gel dehydration and reorganization, and the unhydrated SF particles appear. The gel-like structure, SiO2 and MgO particles are loosely arranged, forming rough and uneven cluster morphology. This study provides an experimental and theoretical basis for the spreading and using MgO-SF materials under high-temperature conditions.

Automated summary

This study investigates the physicochemical properties of MgO-SF cementitious materials at different temperatures. The results demonstrate that MgO-SF materials exhibit excellent high-temperature resistance. The research also reveals the thermal stability of M-S-H gel and the rehydration and decomposition of MgO-SF under high temperatures.