Modeling concrete shrinkage under variable ambient conditions

Drying shrinkage in concrete structures is an important part of the delayed strains. In this paper, drying shrinkage is analyzed and modeled under natural ambient conditions. An experiment on a 30-cm-thick concrete beam, monitored over a period of several years, shows that fluctuations in shrinkage correspond to the average relative humidity of the previous 90 days. Since this property depends on the type of concrete used and the geometry of the beam, we modeled drying and shrinkage of the beam to obtain a model that could be adapted to all types of concrete and geometry. Drying is modeled using a nonlinear diffusion equation, and the shrinkage is simply assumed to be proportional to the weight loss. An initial approach based on these hypotheses, however, does not correspond to the experimental results obtained when there is an increase in the average humidity. If it is assumed, on the other hand, that the diffusivity is lower in the wetting phase, a good approximation to the experimental results can be assumed.