Effect of relaxation on eigenstresses and microcracking in concrete under imposed deformation

For the dimensioning of concrete structures it is customary to determine the forces and stresses occurring in construction elements on the basis of the prescribed loads. In an iterative process, the final dimensions of the elements and reinforcement are then determined. This process becomes less simple if not only the external loads, but also the deformations imposed by shrinkage and temperature change are the cause of forces and stresses. The determination of stresses in the concrete becomes even more complicated if we not only want to know the distribution of forces and the associated stresses in the structures, but also the socalled eigenstresses, which are the result of non-linear temperature and shrinkage fields in concrete cross-sections. These eigenstresses can give rise to microcracks, often in the surface zone of concrete elements. These microcracks can jeopardize the durability of the concrete. With the methods for calculating the force distribution in a concrete construction, these eigenstresses remain out of sight. In current design practice, these eigenstresses are almost never taken into account. The assumption is that as a result of relaxation the eigenstresses largely disappear and will have no influence on the behavior and durability of concrete structures. This research examines whether this assumption is justified...