Determination of isothermal unsaturated capillary flow in high performance cement mortars by NMR imaging

The time-dependent liquid water distribution in cement mortar mixtures during water absorption was determined using a proton nuclear magnetic resonance imaging (NMRI) technique. The variation of the material water diffusion coefficient with the water content was established on the basis of these results. Eight different mortar mixtures were prepared and tested. Test variables included water/binder ratio (0.60, 0.40 and 0.25), type of cement (an ASTM Type 1 cement and a commercial white cement) and the use of silica fume. In addition, the effect of drying treatments on the water transport properties was also investigated. The absorption of water in dry mortars is found to be well described by a non-linear diffusion equation based on the extended Darcy's law of continuum mechanics. Results also confirm that the macroscopic water diffusion coefficient (D(¿)) of mortar is strongly dependent on the material water content. The relationship between the two parameters can be modeled by two exponential equations. Test results finally show that a reduction of the mortar water/binder ratio and the use of silica fume tend to significantly decrease the absorption of water. This phenomenon is well described by the water penetration coefficient ¿max.