Full-scale observation of drying-induced microstructure change in hardened cement paste by water and 2-propanol 1H NMR relaxometry

To understand the microstructural changes in the hardened cement paste during the drying, hardened white Portland cement pastes were D-dried or dried under 11, 33, 40, and 75% relative humidity, and then, pastes were impregnated with 2-propanol or water under vacuum. Measurement of ¹H NMR relaxometry was employed for the pastes before and after impregnation, and the full-scale microstructural changes of the hardened cement paste after drying were successfully visualized. It was observed that the volume of the coarse pores outside the agglomeration of calcium-silicate-hydrate (C-S-H) increased, and the volume of the C-S-H interlayer spaces and gel pores decreased as the drying relative humidity decreased. Thus, it was evidenced that interlayer space is decreasing during drying. It was also confirmed that 2-propanol can enter some of the interlayer space of C-S-H after harsh drying.