Application of spin-spin relaxation to measurement of surface area and pore size distributions in a hydrating cement paste.

Nuclear magnetic resonance (NMR) relaxation analysis has been applied to interpret the evolution of microstructure in a cement paste during hydration. Measurements of transverse magnetic relaxation were made in fully and partially filled white cement pastes for hydration times between 1 h and 6 mo. It was found that only the evaporable water molecules contributed to the echo amplitude in the NMR measurement, while both the evaporable and the hydrated water contribute to the amplitude of the free induction decay. The spin-spin relaxation rate was found to increase markedly during hydration and can be directly related to the total surface area of the CSH gel accessible to evaporable water. The amount of water consumed during the hydration process was determined independently from the amplitude of the NMR echo signal extrapolated to the beginning of the pulse sequence. A numerical inversion of the full spin-spin relaxation profile, determined with a CPMG pulse sequence, was interpreted as a pore volume distribution function. The measurements of total surface area, amount of water consumed, and pore distributions were performed in situ nondestructively, throughout the hydration period for a single sample of cement paste.