Meaning
Diffusion-governed evaporation of water from a porous material follows a rate proportional to the local concentration gradient of moisture. The fickian moisture loss describes this transport process, which dictates how concrete dries from its outer boundaries inward. This mode of drying depends on the relative humidity of the surrounding air and the porosity of the concrete matrix.
Transport Kinetics
Concentration gradients drive the movement of liquid water and vapor through the capillary network. As the concrete dries, the fickian moisture loss decreases over time because the path for moisture escape becomes longer. The rate of drying is highest immediately after stripping the formwork.
Industrial Prediction
Predicting the drying rate of concrete floors prevents the premature application of moisture-sensitive coverings. Engineers utilize the fickian moisture loss model to schedule floor installations and avoid adhesive failures. This calculation is particularly useful when estimating the behavior of thick slabs where moisture takes years to reach equilibrium.
By calculating the moisture profile at different depths, managers can optimize the heating and ventilation schedules of a building. When calculations ignore this diffusion behavior, floors are often covered too early, leading to bubbles and blisters.
Limit Condition
Cracking and carbonation change the microstructural pathways, making simple diffusion models less accurate. The assumption of fickian moisture loss holds best in uncracked concrete exposed to stable environmental conditions. When liquid water is absorbed through rain or washing, capillary suction dominates the transport, requiring a different mathematical description.
