Three-Dimensional Finite Element Analysis Of Fatigue Reflection Crack Propagation In Unbonded Concrete Overlay Pavements

As a typical type of rigid pavements, concrete pavements are widely used in pavement engineering due to their excellent durability and stability. Among various concrete pavement rehabilitation techniques, unbonded concrete overlays(UBCOs) are increasingly popular because of their good performance and efficiency. However, since their design theory is highly simplified and a mechanism for fatigue reflection crack propagation in the UBCO is not well understood, current design approaches are still mechanistic-empirical. Therefore, observing the full process of the fatigue crack propagation, fully understanding its mechanism, and analyzing the influence of the overlay thickness on the UBCO’s fatigue life are crucially meaningful to evaluate the overlay material’s performance, to determine the minimum overlay thickness, and to improve the overlay technique.In order to achieve above goals, numerous literature references haves been studied first. To address their limitations, a fracture mechanics-based approach is proposed. A threedimensional finite element model of the UBCO with an existing crack is established using the general purpose finite element program ABAQUS. The fatigue crack propagation under cyclic moving vehicle loading is simulated using the extended finite element method(XFEM). The mesh quality and mesh sensitivity of the model are systematically investigated to ensure its reliability. Moreover, to determine the values of the materials’ fatigue parameters, simulated results using the same procedure are compared to classic experimental results for agreement. The fatigue parameters are further amended based on the size effect law.Simulation results of the UBCO model show that the fatigue reflection crack exhibits different modes in different propagation stages and locations under varying parameters, although it is mainly type I fatigue crack. Meanwhile, it is observed from the increment rate of the fatigue life that the influence of the cyclic moving loading on the fatigue life decreases when the UBCO is poorly damaged. Furthermore, the thickness of each layer, especially the overlay, has significant effect on the UBCO’s fatigue life. Minimum overlay thicknesses suitable for different traffic conditions has been recommended for the purpose of practical engineering design.