Effect of re-saturation after drying on hydric and strength behaviour of mortar

This experimental study investigates the effect of re-saturation after air-drying and oven-drying at 60 °C on the evolution of hydric and strength behaviour of a standard mortar. Various tests are carried out and lead to the following observations. The swelling occurs relatively quickly, then remains constant and slightly lower than the drying shrinkage for air-dried samples, whereas for oven-dried samples it develops progressively and largely exceeds the drying shrinkage before tending toward stabilisation. The uniaxial compressive strength increases with air and oven-drying in similar proportions. The compressive strength of air-dried samples decreases after one day of re-saturation then increases and overtakes that of saturated samples with time, which mainly indicates a resumption of hydration generated by the drying/re-saturation process that exposes un-hydrated cement to water. However, even if moderately improved after one month of re-saturation, the compressive strength of oven-dried samples almost does not vary any further for six months in remaining lower than that of saturated samples. Moreover, the bending strength increases moderately with air-drying but significantly with oven-drying. With re-saturation, the bending strength of air-dried samples decreases after one day, increases again after one month, then remains constant and lower than that of saturated samples whereas the bending strength of oven-dried samples decreases progressively and more significantly compared to that of saturated samples. All of these results illustrate the significant influence of drying conditioning mode on re-saturated behaviour.