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) Γ₁(Q) and Γ₂(Q), the self-diffusion coefficients D_t1 and D_t2 of water molecules, the average residence times τ₀₁ and τ₀₂, and the proton mean squared displacement (MSD) <u²> are obtained. The results show that the QENS spectra can be fitted very well not only for small Q ( ≤ 1 Å^-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 Ų (the MSD of bound/immobile water) as the Q increases to 1.9 Å^-1, no matter what the temperature and water content are. Furthermore, by the abrupt changes of the fitted values of D_t1, τ₀₁, and Γ₁(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.