Self-Diffusion of Water in Cement Pastes as Studied by 1H PFG NMR and DDCOSY NMR

Abstract

The chapter considers the data of one-dimensional 1H NMR diffusion studies in white Portland cement paste (the water-cement ratio (w/c) = 0.4) with the age of 1 to 14 days and 1 year. Two-dimensional diffusion-diffusion correlation (DDCOSY) experiments have been carried out in cement paste (w/c= 0.4) aged from 1 to 7 days. It was found that the 1H pulsed field gradient (PFG) NMR experiments measure diffusivities of capillary water. A log-normal pore size distribution and relaxation times dependent on pore size have been applied to fit the data. Mature paste has been characterized by mean capillary pore size of 4.2 μm. The data for cement pastes with the age of 1 week showed similarity. On the basis of data obtained it was suggested that gel porosity and hydrates do not form in the capillary porosity. 2D DDCOSY experiments did not discover any diffusion anisotropy in capillary pores.

Keywords: 2D diffusion-diffusion correlation NMR spectroscopy (DDCOSY), Apparent diffusion coefficient Dapp, Cement paste, Diffusion time (Δ), Inverse Laplace transform (ILT), Length of gradient pulse (δ), Pulsed Field Gradient (PFG) NMR, Restricted diffusion, Spin-lattice relaxation time T1, Spin-spin relaxation time T2, Stimulated echo (STE), Water.