Research on Hydration of Cement at Early Age by Proton NMR

Changes of initial distribution,weighted mean values and total signal intensity of longitudinal relaxation time(T_1) of water in fresh cement pastes as a function of hydration time and its correlation with hydration process during the early age was studied with low field proton nuclear magnetic resonance(NMR).T_1 distribution curves at initial time exhibit two peaks.The main peak is related to water filling in space around the cement grains while the minor one represents the water constrained in flocculations.The evolution curves of weighted mean values of T_1 are in good agreement with the hydration process of cement pastes and could be roughly divided into four stages: initial period,dormant period,accelerated period and steady period.The total signal intensity detected in experiments is proportional to the amount of physically bound water in the pastes.Since the transition from physically to chemically bound water,the relative percentage decreases as the hydration time increases.