Mesoscale modelling of the FRP-concrete debonding mechanism in the pull-off test.

This study comprehensively investigated the FRP-concrete debonding mechanism in the pull-off test using a mesoscale cohesive zone modelling approach. Pull-off tests were performed on the FRP-strengthened concrete elements, and corresponding 2-D mesoscale finite element models were established. The numerical stress-separation responses and strain/crack initiation and propagation in the pull-off test were examined. Subsequently, a parametric study numerically investigated the effect of adhesive and FRP properties, concrete heterogeneity, loading fixture stiffness, and sample scale on the debonding mechanism. Finally, the 2-D mesoscale model was extended to the 3-D. The main conclusions are: (1) global separation between FRP and concrete in the pull-off test is minimal; (2) the normal bond strength of the epoxy resin-concrete interface controls the failure mode; however, FRP stiffness does not affect the result; (3) the aggregate content and mortar porosity significantly influence the bond strength, and the effect of aggregate shape and gradation is slight; (4) the loading fixture stiffness should increase with an increase in sample size; (5) the pull-off bond strength aligns with the size effect theory; (6) the bond stiffness and strength of the 3-D model is significantly greater than that of the 2-D model, which is attributed to the out-of-plane concrete constraining. [ABSTRACT FROM AUTHOR]