Influential Depth by Water Absorption and Surface Drying in Concrete Slabs

Water is one of the major factors that contribute to the deformation and deterioration of concrete structures. The top surface of structures such as slabs or pavements on the ground can be subject to external drying, and the bottom surface can be in contact with water from ineffective drainage. A knowledge of moisture distribution significantly improves durability prediction. The water-to-cement ratio, the environment relative humidity (RH), and the moisture transport properties of concrete affect moisture distribution in slabs. This study investigated the effects of surface drying, self-desiccation, and bottom water absorption on moisture profiles in concrete slabs at water-to-cement ratios of 0.3, 0.4, and 0.5. The RH distributions along slab depths were measured continuously from final set with specially designed RH sensors. The hydraulic diffusivity of concretes was obtained through sorptivity testing. An analytical procedure that considered external drying, self-desiccation, and water absorption was implemented for RH simulation of slabs exposed to different environmental conditions. Experimental measurements and simulations showed that the influential depth is about 50 to 100 mm from the external surface drying. The influential depth from water absorption is about 50 mm. An equivalent temperature gradient (Delta T-e) can be used to quantify the moisture gradient effect. Given that the environmental conditions are the same, the analytical simulation suggests that greater Delta T-e results in a concrete slab with a higher water-to-cement ratio.