SURFACE MAGNETIC-RELAXATION IN CEMENT PASTES

Surface magnetic relaxation in porous media is usually attributed to h indered rotation or to paramagnetic impurities on the surface. In ceme nt pastes, however, it seems reasonable to attribute surface relaxatio n to dipole interactions in water adsorbed as water of hydration on gr ain surfaces. The rate limiting factor would then be the exchange rate between mobile water in the pores and adsorbed water. The hydrate rel axation time is 17 mu s while the measured surface relaxation time is 30-40 mu s. This difference is explained if the exchange time between mobile and adsorbed water is about the same as the relaxation time of the water of hydration. The exchange model also suggests that the surf ace relaxation time should decrease with temperature. Measurements tes ting this theory are now being prepared.