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.