Quasielastic neutron scattering study of the effect of water-to-cement ratio on the hydration kinetics of tricalcium silicate

Quasielastic neutron scattering (QNS) measurements of the hydration kinetics of tricalcium silicate (C₃S) have been made with 60 μeV energy resolution at a momentum transfer q = 1 Å^-1. Monitoring the fraction of neutrons elastically scattered from C₃S paste specimens follows the progress of the C₃S hydration reactions. Three different water/cement ratios (w/c = 0.3, 0.5, and 0.7) were studied in this experiment. Analysis of the rate of reaction over the first approximately 15 h was by an Avrami model. After this time, the rate of hydration no longer follows nucleation and growth kinetics but enters a diffusion controlled regime. At this point, the rate of hydration depends strongly on the w/c, with more reaction at higher w/c ratios. A shrinking core model was used to analyze the diffusion-limited portion of the reaction at later times. The values of the apparent diffusion constant obtained from these data indicate a log-linear relationship between the diffusion constants and the w/c ratio.