2023 Volume 77 Issue 1 Pages 17-25
The structure of the C-S-H gel, the distribution of mobile water in the pores, and the amount of chemically bound water in hydrates in hardened cement paste vary with external relative humidity （RH）. In addition, hysteresis due to drying history exists, so that the properties of virgin-dried and subsequent re-humidified systems differ even when they are in equilibrium at the same RH. In this study, hardened cement pastes which was virgin-dried at RH 60％ and those re-humidified at RH 60％ after RH 23％ and D-dry drying were measured with 1H NMR Relaxometry, water vapor adsorption isotherm, TG, and XRD. It was confirmed that the decrease in interlayer distance due to RH 23％ and D-dry drying was not recovered by subsequent re-humidifying. In addition, the formation of new gel pores was observed after those drying processes. Changes in gel water and interlayer water content and AFt content due to drying and re-humidifying were quantitatively evaluated.
