The roles of hydration and evaporation during the drying of a cement paste by localized NMR

The moisture distribution during the setting of a thin mortar layer can be particularly complex to manage under dry (20% RH) and hot weather (above 25 °C) conditions. To better understand the fundamental phenomena at stake, we used static gradient relaxation NMR tools such as Profile MOUSE and STRAFI. This allowed disentangling the mutual effect of evaporation and self-desiccation by hydration. The interest of combining the two techniques is that the capillary water is observed with the MOUSE while STRAFI reveals quantitatively the build-up of the hydrate gel nanostructure. Spatially resolved and 2D relaxation exchange experiments on a model white cement paste revealed that although evaporation induced a capillary water gradient, the kinetics of the building of the pore structure and its homogeneity remained unaffected.