Drying effect on cement paste porosity at early age observed by NMR methods

Nuclear Magnetic Resonance (NMR) methods (imaging and relaxation time) allow to study the water content and the pore size distribution in cementitious materials. Hydration of cement pastes with two water to cement ratios W/C (W/C = 0.4 and W/C = 0.45) has been studied under two conditions (with drying or without drying) at early age. The objectives of this study were, firstly (i) to determine the water content and the drying mechanisms with Magnetic Resonance Imaging (MRI) and to validate these results with oven-drying methods and secondly, (ii) to analyse the cement paste porosity modifications due to drying exposure with distribution of T1 relaxation times, which are compared to by Mercury Intrusion Porosimetry and N2 gas adsorption measurements. The results of this study highlight the pertinence of NMR and associated methods to understand mechanisms of hydration of cementitious materials and especially the influence of drying on hydration process and on microstructure of the materials.