NEUTRON-SCATTERING STUDIES OF HYDRATING CEMENT PASTES

The progress of the hydration reactions of tricalcium silicate (C3S) h as been followed using quasielastic neutron scattering (QNS) at an ene rgy resolution of 60 mu eV and a momentum transfer of q = 1 Angstrom(- 1). The degree of reaction in the hydrating cement paste is inferred f rom the fraction of water that is chemically bound to the cement react ion products and the known stoichiometry of C3S hydration. Three diffe rent water-to-cement ratios were studied in this experiment: W/C = 0.7 , 0.5 and 0.3. The results of an Avrami-model analysis of the first 15 h of the reaction are consistent with three types of C3S-H2O reaction product morphology and growth mechanisms: (i) a plate-type product ph ase from either phase boundary growth with no nucleation; (ii) diffusi on-limited growth with constant nucleation; or (iii) a needle-type pro duct phase with phase boundary growth and constant nucleation. Analysi s of the later-time diffusion-limited portion of the reaction provides apparent diffusion constants for the migration of water through the C 3S hydration products. These data indicate that the diffusion constant s vary approximately exponentially over the range of water-to-cement v alues studied. (C) 1998 Elsevier Science B.V. All rights reserved.