Proton NMR Relaxometry of Portland Cement Hydration

In situ proton NMR relaxometry measurements on the hydration of Portland cement pastes were carried out to follow the hydration process. The spin-spin (T$_{2})$ relaxation times are about 3 orders of magnitude smaller than the spin-lattice relaxation times (T$_{1})$, indicating the presence of high amounts of paramagnetic ions. The hydration time dependence of T$_{2}$ is still determined by the confined nature of exchangeable water in the micropores. T$_{1}$ evolution with hydration time is dominated by the enhanced self-diffusion due to fast molecular exchange of confined water molecules. A ``hump'' structure is seen in T$_{1}$ during the middle stages of hydration and is attributed to the development of transient high concentration of polymeric ions in the solution phase. The present NMR investigations provide convincing evidence that even in the presence of high concentrations of paramagnetic impurities, molecular self-diffusion is the principal mechanism governing the spin-lattice relaxation of fluids confined in porous media.