Asphalt Pavement Fatigue Cracking Modeling.

Abstract

Fatigue is a major structural distress that leads to a reduction in the serviceability of asphalt pavements. In a mechanistic pavement design, asphalt fatigue cracking is considered as one of the three design criteria along with rutting and low-temperature associated cracks. The successful application of this design method to practice thus relies on a reliable crack prediction model. Most existing crack prediction models are based on the results of laboratory beam fatigue tests. Beam tests are not adequate because they can't realistically simulate the propagation of a crack in an asphalt pavement layer. This research studied the asphalt cracking through fatigue tests conducted on asphalt slabs taken from experiment pavements, which can more closely reflect the three dimensional characteristic of a pavement crack than beam fatigue tests. To model the cracking process in asphalt slabs, the stress intensity factor was evaluated for cracked slabs based on three-dimensional FEM models. The fatigue crack, at the underside of a slab, was simulated as a semi-elliptical surface crack. The J-integral approach was used from which the stress intensity factor was calculated. In asphalt slab fatigue tests, the loading cycles for defined crack initiation and propagation stages were recorded for developing crack prediction models. Based on the results of stress and stress intensity factor analyses and asphalt slab fatigue tests, two crack initiation and. propagation relationships were developed for predicting asphalt fatigue life. The crack initiation relationship was based on the critical stress and strain and the crack propagation relationship used the stress intensity factor as an estimator. The fracture parameters, C and n, were also determined based on asphalt slab fatigue tests. The proposed fatigue life prediction relationships were used to estimate the fatigue fives of the pavements at LTRC-ALF experiment site. The existing equations were used to evaluate the stress intensity factor for a fatigue crack in asphalt pavement layer. The predicted results were compared with the observed pavement life. It was found that the predicted pavement life based on the proposed relationship was very close to the observed pavement life.