Microwave dielectric study of water structure in the hydration process of cement paste

Microwave dielectric relaxation measurements, via the time-domain reflectometry method, were performed on portland cement paste for the first time, and the water structure during the hydration process was observed. The relaxation process due to the orientation of free water, which is independent of calcium silicate hydrate (C-S-H), was observed at similar to 10 GHz. The relaxation strength, in proportion to the amount of free water, decreased rapidly as the curing time increased for the first three days. This change is in good agreement with that of a chemical reaction that was reported by measurements of the heat that is evolved during hydration, The free water is taken into C-S-H and is transformed to hydrated water by the hydration process. When hydration proceeds, the relaxation processes due to the orientation of the hydrated water in C-S-H occur at similar to 100 MHz and 1 MHz.