Dynamic behaviors of water contained in calcium–silicate–hydrate gel at different temperatures studied by quasi-elastic neutron scattering spectroscopy

The dynamic behaviors of water contained in calcium-silicate-hydrate (C-S-H) gel with different water content values from 10% to 30% (by weight), are studied by using an empirical diffusion model (EDM) to analyze the experimental data of quasi-elastic neutron scattering (QENS) spectra at measured temperatures ranging from 230 K to 280 K. In the study, the experimental QENS spectra with the whole Q-range are considered. Several important parameters including the bound/immobile water elastic coefficient A, the bound water index BWI, the Lorentzian with a half-width at half-maximum (HWHM) Gamma(1)(Q) and Gamma(2)(Q), the self-diffusion coefficients D-t1 and D-t2 of water molecules, the average residence times tau(01) and tau(02), and the proton mean squared displacement (MSD) < u(2)> are obtained. The results show that the QENS spectra can be fitted very well not only for small Q (<= 1 angstrom(-1)) but also for large Q. The bound/immobile water fraction in a C-S-H gel sample can be shown by the fitted BWI. The distinction between bound/immobile and mobile water, which includes confined water and ultra-confined water, can be seen by the fitted MSD. All the MSD tend to be the smallest value below 0.25 angstrom(2) (the MSD of bound/immobile water) as the Q increases to 1.9 angstrom(-1), no matter what the temperature and water content are. Furthermore, by the abrupt changes of the fitted values of D-t1, tau(01), and Gamma(1)(Q), a crossover temperature at 250 K, namely the liquid-to-crystal-like transition temperature, can be identified for confined water in large gel pores (LGPs) and/or small gel pores (SGPs) contained in the C-S-H gel sample with 30% water content.