Microstructure of Alkali-Activated Slag in Ultralow Temperature Environments

In this study, the changes in the phase and microstructure of alkali-activated slag (AAS) in ultralow-temperature environments (-170 degrees C) was experimentally studied by means of X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, thermal gravimetric (TG), scanning electron microscopy energy dispersive X-ray spectroscopy (SEM-EDS), Si29 magic-angle spinning nuclear magnetic resonance (MAS NMR), and pore structure. The results show that as the modulus of water glass increased, the mass loss of AAS after the ultralow-temperature freeze-thaw cycles (ULT-FTC) decreased, the freeze-thaw resistance increased. The ULT-FTC caused the internal structure of the AAS samples using different activators to slip and rearrange. Partial calcium-(alumina)-silicate-hydrate gel [C (A) S H] gel was decalcified. The gel structure formed using 2.0 M water glass as the activator was the most stable. The dense structure with a lower Ca/Si ratio enables the AAS to maintain a relatively stable microstructure after undergoing ULT-FTC.