This work aimed to gain a better understanding on the mechanisms of creep/microcracking coupling with changes in water content, and to develop a numerical creep/damage model at the mesoscale for the prediction of long-term delayed strains. Creep of concrete depends on multiple coupled factors among which microcracking is of major significance.

In order to predict in a reliable manner the long term performance of nuclear civil engineering structures, concrete constitutive models require a basis on realistic deformation mechanisms at the micro scale. The delayed strains induced by creep and shrinkage are the cause of a loss of prestress that may increase the risk of potential leaks in accidental conditions. The safety of double wall concrete containment buildings in the French nuclear fleet primarily depends on the integrity of prestressed concrete.

For larger values of pull-out displacements, more diffuse damage of the fiber–matrix interface was observed between the ribs, especially in plaster matrices. These results suggest that fiber–matrix interlocking may be affected by geometry-driven tensile stiffening effects between the ribs. Vertical strain concentrations were observed in correspondence to lateral protrusions (or ribs) of the reinforcing fibers. An articulated load transfer mechanism between the fiber and the matrix was observed in the examined tests, as demonstrated by zigzagged distributions of vertical displacement jumps and vertical strain profiles in the fibers at the initial stages of pull-out. Profiles of normal, tangential and vertical displacement jumps as well as vertical strains in the fibers were used to study interfacial debonding. Relative motions at the interfaces were measured thanks to adapted meshes with split nodes. Three pull-out tests were carried out inside of an X-ray tomograph allowing for Digital Volume Correlation analyses. The quantification of debonding was performed for additively manufactured “fractal” fibers embedded within two brittle matrices.

Ct flexture