2-DIMENSIONAL NUCLEAR-MAGNETIC-RESONANCE STUDY OF A HYDRATED POROUS-MEDIUM - AN APPLICATION TO WHITE CEMENT

Structure and dynamics of a hydrated white cement were investigated by the T-1-weighted lineshape, two-dimensional (2D) exchange, and 2D sep aration of inhomogeneous and homogeneous lineshapes nuclear magnetic r esonance (NMR) techniques. T-1 weighting of the proton spectrum elimin ates the strong bulk water signal from the pores so that the weaker sp ectrum of the solid cement matrix becomes observable. The proton spect rum of the solid cement fraction exhibits a characteristic Fake double r shape and shows a close similarity to the powder spectra of pure cal cium hydroxide and the crystalline water of gypsum. The 2D exchange NM R spectrum of white cement demonstrates the existence of slow chemical exchange processes of protons in the solid matrix on a sub-kHz freque ncy scale. This exchange is orders of magnitude slower than the exchan ge between the surface and bulk water. The 2D NMR separation of inhomo geneous and homogeneous lineshapes technique demonstrates that the abs orption lines of a set white cement are inhomogeneously broadened due to the existence of a distribution of static local magnetic fields. Th e major contribution to these fields comes from the dipolar fields of the paramagnetic electrons whereas the magnetic susceptibility differe nces of the liquid and solid fractions add a small part at the solid-l iquid boundary where the direction of the external magnetic field is c hanged. (C) 1998 American Institute of Physics. [S0021-8979(98)04607-6 ].