Fracture of asphalt concrete: A cohesive zone modeling approach considering viscoelastic effects

Asphalt concrete is a quasi-brittle material that exhibits time and temperature dependent fracture behavior. Softening of the material can be associated to interlocking and sliding between aggregates, while the asphalt mastic displays cohesion and viscoelastic properties. To properly account for both progressive softening and viscoelastic effects occurring in a relatively large fracture process zone, a cohesive zone model (CZM) is employed. Finite element implementation of the CZM is accomplished via user subroutines that can be used in conjunction with general-purpose software. The bulk properties (e.g. relaxation modulus) and fracture parameters (e.g. cohesive fracture energy) are obtained from experiments. In this study, artificial compliance and numerical convergence (which are associated with the intrinsic CZM and the implicit finite element scheme, respectively) are addressed in detail. New rate-independent and rate-dependent CZMs, e.g. a power-law CZM, tailored for fracture of asphalt concrete are proposed. A new operational definition of crack tip opening displacement (CTOD), called delta25, is employed to considerably minimize the contribution of bulk material in measuring fracture energy. Predicted numerical results match well with experimental results without calibration. Simulations of various two- and three-dimensional mode I fracture tests, e.g. disk-shaped compact tension (DC(T)), are performed considering viscoelastic effects. The ability to simulate mixed-mode fracture and crack competition phenomenon is demonstrated in conjunction with single-edge notched beam (SE(B)) test simulation. The predicted mixed-mode fracture behaviors are found to be in close agreement with experimental results. Fracture behavior of pavement under tire and temperature loadings is explored.