Dynamic microstructural evolution of hardened cement paste during first drying monitored by 1H NMR relaxometry

In this study, the rate of change of microstructural re-organization in hardened cement paste under the first drying, which is caused by the colloidal nature of calcium-silicate-hydrate (C-S-H), is confirmed via 1H nuclear magnetic resonance relaxometry. Under the first drying, water evaporates from larger pores, while the interlayer water begins to increase. During the mass change, interlayer water continues to increase until reaching a peak. After the peak has been reached, interlayer water gradually decreases, while interhydrate water and capillary water appear with little observable change in mass. Based on the data, gel pores and interlayer spaces are considered to share movable C-S-H sheets, and removal of water from such pores causes a change in distance between C-S-H sheets, which transforms gel pores to interlayer spaces.