Abstract
To gain a more direct insight into nature of water in contact with calcium silicate hydrate (C-S-H), the main component of hardened cement, deuterium (2H or D) quadruple echo NMR (nuclear magnetic resonance analysis) spectra, deuterium relaxation time T1 and rotational correlation time τc were determined from white Portland cement and 2H2O mixtures subjected to different relative humidity curing conditions, (RH) 98, 60, 33 and 11%, for 91 days. The 2H NMR spectra shows two signals: a sharp central signal at 0 kHz and outer symmetric signals around ±100 kHz. The central signal is considered to belong to mobile deuterium and the outer symmetric signals are considered to belong to immobile deuterium. The strength of the central signal decreases with increasing curing RH, but even the RH 11% sample has shows a signal strength that indicates the existence of both mobile and rigid deuterium in the sample. The study on relaxation time T1 and rotational correlation time τc indicates that the signal of central signal contributes the mobile state deuterium can be distinguished into two different components by τc: a faster τc component is comparable to the liquid state and a slower τc showing restricted movement of the water. Previous studies have shown two water states near the surface of pores in C-S-H; one is a single-layer of adsorbed water like on the surface of protein and the other is a several layer thick ‘semi-adsorbed’ water layer around the absorbed water. Further, the water generating the slower τc value could belong to such adsorbed water and the faster τc value could be assigned to semi-adsorbed water. These results will help to describe and evaluate the structure changes of C-S-H induced by the relative humidity at curing.
