Influences of water by cement ratio on mechanical properties of mortars submitted to drying

Concrete materials are submitted to drying when the relative humidity of their surrounding is decreasing. The main purpose of this study is to highlight the variation of multiaxial mechanical behaviour of mortars which depends on desiccation level and cement paste properties (quality). The behaviour under discussion includes uniaxial and triaxial strengths, elastic properties and volumetric strains due to hydrostatic loading. Multiaxial experiments, carried out on two mortars for which the only difference was the water by cement ratio (w / c = 0.5 and 0.8), show a competitive effect between the increase in material rigidity due to capillary suction and saturation gradients, and the microcracking which comes from material heterogeneity and differential shrinkages of the sample. This effect mainly depends on cement paste properties and its porosity; therefore the capillary suction effect is preponderant for a high paste quality (i.e. lower porosity) while a low paste quality would be more sensitive to microcracking.