Modeling Reflective Cracking Development In Hot Mix Asphalt Overlays And Quantification Of Control Techniques

Hot-mix asphalt (HMA) overlay is regarded as an efficient method to rehabilitate moderately deteriorated pavements. Despite the application of an adequately designed overlay, when HMA overlays are built on jointed concrete pavement (JCP) or a cracked surface, reflective cracking can develop shortly after the overlay application due to traffic loads and environmental changes. Several remedial techniques, including interlayer systems, have been incorporated into HMA overlays to control reflective cracking. This study examined the behavior of traffic-induced reflective cracking using a finite element (FE) model for an HMA overlay with and without interlayer systems, and evaluated the performance of interlayer systems in controlling reflective cracking. To achieve these objectives, a three-dimensional FE model was built for a typical HMA overlay constructed over JCP. A linear viscoelastic model and a bilinear cohesive zone model (CZM) were incorporated into the FE model to characterize continuum and fracture behavior of the HMA. Using the bilinear CZM, reflective cracking initiation and propagation were simulated. Transient moving vehicular loading was applied across a joint to develop reflective cracking. In order to force reflective cracking development by one pass of load application, various levels of overload were applied. Two distinct interlayer systems, sand mix and steel netting with slurry seal, were examined for their effectiveness in controlling reflective cracking. The sand mix was modeled with the LVE model and bilinear CZM. The steel netting interlayer system was modeled with beam elements for steel wires and membrane elements for slurry seal. To quantify the status of reflective cracking development, a representative fractured area (RFAOL), that is an equivalent stiffness degradation in the entire HMA overlay, was used. A limit state load approach was used to determine the resistance of the HMA overlay to reflective cracking in terms of normalized axle load of an overload equivalent to a 80-kN single-axle load. The service life of the HMA overlay regarding reflective cracking was specified by the number of load repetitions based on the Paris law. A reflective cracking control factor was defined as the ratio of the service life to the HMA overlay without an interlayer system; the factor was used to evaluate the performance effectiveness of these interlayer systems in controlling reflective cracking. It was found that the bearing capacity of existing JCP played an important role in developing reflective cracking. Reflective cracking potential increased inversely with the modulus of base and subgrade layers. Interface bonding conditions, especially bonding strength, affected the development of reflective cracking. Lower interface bonding strength resulted in greater potential for developing reflective cracking. The study concluded that the sand mix interlayer system extended the service life of the HMA overlay regarding reflective cracking due to its relatively high fracture energy. A macro-crack level of reflective cracking was initiated in the wearing course in the HMA, so-called crack jumping. The softer the sand mix, the tougher it may be, but it may cause shear rutting in HMA overlay. Hence, sand mix fracture energy and thickness thresholds should be identified. The steel netting interlayer system performed better than the sand mix; the performance of the latter is thickness and fracture energy dependent. When the steel netting interlayer system was installed properly, the reflective cracking service life of the HMA overlay was found to be six times longer than that of the HMA. The performance was still better than sand mix when localized deboning induced. However, severe debonding of steel netting can be detrimental to its performance.