Composite specimen testing to evaluate the effects of pavement layer interface characteristics on cracking performance

Open graded mixture which is widely used for Open Graded Friction Course (OGFC) has considerably lower values of fracture energy density and dissipated creep strain energy density to failure than dense-graded mixture. Since those OGFC may be 'first front' in resisting top-down cracking, previous research has suggest that the quality of the OGFC mixture and the bond between OGFC and the structural layer affects top-down cracking performance. The primary objective of this study is to identify a method to evaluate the effect of interface bonding condition on top-down and reflective cracking within the composite pavement system.;A composite specimen interface cracking (CSIC) test was developed to evaluate the effects of pavement layer interface characteristics on cracking performance. The following factors were considered and evaluated when developing the testing system: loading mode, specimen symmetry, stress concentration method and specimen curved end surface reinforcement. Proper data collection and interpretation methods were developed to properly account for the complex stress distribution and progressive damage during the test. Three types of interface conditions were evaluated for top-down cracking, while two types of interface conditions were evaluated for reflective cracking. In addition, the effect of OGFC on top-down cracking was evaluated using this newly developed test method. NovabondRTM when used as a bonding agent between the OGFC and underlying structural layer, polymer modified asphalt emulsion (PMAE), increased the top-down cracking performance of composite pavement. More generally, it was determined that the effectiveness of bonding agent is closely related to its brittleness. Trackless tack coat, which is also polymer modified, but much more brittle than NovabondRTM, was determined to have a negative effect on top-down cracking performance. As compared with conventional tack coat, NovabondRTM was determined to improve the reflective cracking resistance of composite pavement. NovabondRTM application rate was determined to have a significant effect on the top-down and reflective cracking resistance. The introduction of an OGFC with conventional tack coat on dense-graded mixture was determined to reduce the cracking resistance of composite pavement as compared with pavements without OGFC. The research clearly illustrated the importance of interface bond and flexibility on top-down and reflective cracking performance.