Multiscale modeling of concrete and of the FRP-concrete interface

Cracking and failure processes in concrete members as well as debonding mechanisms between concrete surfaces and fiber-reinforced polymer composites used for structural strengthening are often modeled through macroscopic empirically-based cohesive zone models. This approach presents a number of limitations, as macroscopic laws spatially homogenize complex damage and failure processes taking place at the lower scales. This paper proposes a multiscale approach for concrete and for the determination of mixed-mode cohesive zone models for the composite-concrete interface based on mesomechanical analysis. The mesomechanical model includes the explicit description of the heterogeneous material geometry close to the interfacial zone, as well as a continuum damage description for both the cement matrix and the matrix-aggregate interfacial transition zone. Macroscopic mixed-mode cohesive zone laws are then obtained through a numerical homogenization procedure. The choice of the representative volume element is discussed and the cohesive behavior under mode-I, mode-II and loading conditions with different degrees of mode mixity is analyzed. Comparisons with available experimental and analytical results are also performed.