Mechanical and microstructural property evolutions of MgO-slag cementitious materials under high temperatures

The property evolutions of MgO-slag cementitious materials at 20 degrees C, 100 degrees C, 200 degrees C, 300 degrees C, 400 degrees C, 600 degrees C and 800 degrees C are evaluated comprehensively, and the microstructural evolutions are revealed by X-ray diffraction (XRD), Raman spectroscopy, Mercury intrusion porosimetry (MIP) and Scanning electron microscope (SEM) tests. The results demonstrate that MgO-slag cementitious materials have good high-temperature resistance. At 800 degrees C, C-S-H and C-A-S-H have a relatively stable structure after dehydroxylation, and brucite is dehydroxylated to form MgO. The compressive strength after high temperatures is related to the formation of brucite, C-S-H, and CA-S-H. The greater the formation of brucite, the smaller the reduction rate of compressive strength at 800 degrees C. At 200 degrees C or 300 degrees C, the peaks of brucite and C-S-H are higher, resulting in an increase in compressive strength; At 600 degrees C and 800 degrees C, the structure of the hydrated product crystallizes seriously, the cohesion between the gel phase particles decreases, and the hydrated product crystallizes and reorganizes after dehydroxylation. High temperature causes changes in internal hydration products and pore structures, and the whole process is related to the formation of additional products, dehydration and crystallization, which can be explained by XRD, Raman spectroscopy, MIP and SEM tests. The microstructural test results are related to mechanical behaviors.