Drying shrinkage in concrete structures is an important part of the delayed
strains. In this paper, drying shrinkage is analyzed and modeled under nat
ural ambient conditions. An experiment on a 30-cm-thick concrete beam, moni
tored 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 co
uld be adapted to all types of concrete and geometry. Drying is modeled usi
ng a nonlinear diffusion equation, and the shrinkage is simply assumed to b
e proportional to the weight loss. An initial approach based on these hypot
heses, however, does not correspond to the experimental results obtained wh
en there is an increase in the average humidity. If it is assumed, on the o
ther hand, that the diffusivity is lower in the wetting phase, a good appro
ximation to the experimental results can be assumed.