Mesoscale modelling of concrete damage in FRP-concrete debonding failure

It is challenging to simulate fibre-reinforced polymer (FRP)-concrete debonding failure in detail because concrete damage usually occurs with a thin layer of mortar debonding attached to the FRP. This study applied a single-lap shear test with a digital image correlation technique to externally bonded FRP-strengthened concrete elements. An improved random walk algorithm method generated a realistic mesostructure of concrete. The twodimensional mesoscale finite element model for FRP-strengthened concrete was established. The cohesive interface elements were inserted along all mortar-aggregate interfaces. Concrete damaged plasticity and cohesive zone model were applied to simulate the nonlinear properties of mortar and mortar-aggerate interface, respectively. The experimental and numerical load-displacement curves, strain/stress distribution, and local bond-slip curves were obtained and compared. A numerical parametric study investigated the effects of the aggregate, mortar, and adhesive on debonding failure. The main conclusions are: (1) the initiation and propagation of mortar damage and mortar-aggregate interface cracking in the FRP debonding process were directly conducted by the mesoscale model; (2) the numerical curves showed considerable oscillation, possibly due to the stress concentration near the aggregate boundary when the crack transmitted the aggregate, and the stiffness decreased after cracking was initiated at the mortar-aggregate interface; (3) concrete damage may extend to a depth of 25 mm, indicating that the concrete damage is greater than a thin layer of mortar debonding observed in the test; (4) applying polygonal aggregates, increasing aggregate size and surface mortar thickness, and reducing the adhesive layer thickness improves bond performance.