Reflective cracking of flexible pavements: Literature review, analysis models, and testing methods

Hot mixed asphalt (HMA) overlay is one of the commonly used methods for rehabilitating deteriorated pavements. The Nevada Department of Transportation (NDOT) uses HMA overlays as a rehabilitation technique for the majority of the state's flexible pavements. One major type of distress influencing the life of an overlay is reflective cracking. In the past, NDOT has experimented with a number of techniques to reduce the impact of reflective cracking on HMA overlays like cold in-place recycling, reinforced fabrics, stress relief courses, mill and overlay, Portland Cement Concrete (PCC) rubblization, and PCC crack and seat.; In 2006, the Nevada DOT initiated a three-phase research project to identify the promising techniques to mitigate reflective cracking in HMA overlays: (a) Phase I: Review of literature and the performance of the various techniques in Nevada, (b) Phase II: Identify analysis models and laboratory tests, and (c) Phase III: field verification of the selected techniques.; A literature review was conducted for the current and previous efforts outside Nevada on the reflective cracking mitigation techniques in HMA overlays. The standard specifications on the reflective cracking mitigation techniques from all fifty state DOTs were reviewed and summarized. Thirty two states out of fifty have specified a reflective cracking control system in their current standard specifications.; Based on the review of the currently available analytical models to predict the resistance of HMA overlays to reflective cracking, three design methods were identified and summarized: (1) Virginia Tech Simplified Overlay Design Model; (2) Rubber Pavements Association Overlay Design Model; (3) The New AASHTO model for Reflective Cracking.; An overlay design was conducted for three different HMA overlay mixes according to the three identified overlay design methods. In a summary, the Virginia Tech method showed a thinner overlay thickness for the stiffer mix whereas, the Rubber Pavements Association method, which considers both stiffness and fatigue characteristics of the mix, the overlay thickness was dependent on the interaction between the two material properties. On the other hand, a unique and thick overlay thickness was found with the new AASHTO method as it does not consider the material properties of the overlay mix as part of the design.; Additionally, a literature review was performed for the available laboratory tests to evaluate the resistance of HMA mixtures to reflective cracking. None of the reviewed laboratory test methods has undergone field validation except the Texas Transportation Institute (TTI) Overlay Tester which showed consistency between the mixtures' test results and their corresponding field performance. The TTI Overlay Tester results on the cores taken from different highway projects showed that asphalt mixtures performed very well in the field when the reflective cracking life (from the overlay tester) is larger than 300.; Finally, based on the analysis of the various findings it was recommended to: (1) Further evaluate the stress relief course as a reflective cracking mitigation technique under Nevada's conditions. (2) Use the TTI Upgraded Overlay Tester to evaluate mixtures in the Laboratory for reflective cracking resistance. (3) Use the Rubber Pavements Association Overlay Design Model to design the require overlay thickness.