A multiphysics model for concrete at early age applied to repairs problems

Experience has shown that the repairs of concrete structures are often subject to premature cracking induced by the strain incompatibilities between the substrate and the hardening material of restoration. The thermo-hygro-mechanical behavior of cementitious materials is very complex especially during the first hours after the cast, when various physical and chemical phenomena determine thermal, hygral, chemical and viscous strains. To quantify these deformations by means of a mechanistic approach, a multiphysics model has been developed a few years ago by Gawin et al. (2006) [1], [2]. Nowadays, this model has been enhanced for structural applications, and has been implemented in 3D in Cast3M (the finite element code developed by the CEA, French Atomic Agency [3]). In this paper the most important aspects of the model and the numerical analysis of the behavior of a real repair case are presented. Two repaired beams are modeled. It is shown that, despite cracking induced by shrinkage restraint, when the repair concrete is similar to that of beam, the mechanical behavior of the repaired beam is similar to the sound one (reference beam), in term of stiffness and bearing load. Besides, the mechanical behavior of the beam repaired using an ultra-high performance fiber reinforced concrete is quite better than that of the reference one.