Mechanisms of asphalt cracking and concrete-asphalt debonding in concrete overlay on asphalt pavements

The research presented in this paper identifies several distress mechanisms that asphalt base and concreteasphalt interphase may experience in concrete overlay on asphalt (COA) pavements. The identification of the distresses is based on visual examination of cores extracted from a relatively large pool of COA test sections in a dry climate. Concrete-asphalt debonding was particularly severe at the transverse joints of 3.6 m (12 ft) long slabs as compared with 1.8 m (6 ft) long slabs. Transverse joint propagation into the asphalt base was observed in the shorter slabs. The debonding and the propagation of the transverse joints into the asphalt base negatively impacted the capacity of concrete-asphalt composite structure to resist traffic loading and the load transfer efficiency (LTE) of the transverse joints. Based on the analysis of the structural response of the test sections and finite element method modeling, two main distress mechanisms were identified. The first mechanism is the curling and warping of the slabs under thermal and drying shrinkage actions. This mechanism produces very high tensile and shear strains at the concrete-asphalt interphase likely to cause concrete-asphalt debonding starting at the transverse joints. The second mechanism is traffic-induced shearing of the asphalt below the transverse joints likely to cause cracking of the underlying asphalt. The results indicate that for the dry and hot climates such as California the contribution of the asphalt base to the COA structure may be far from ideal and two common assumptions of the mechanistic-empirical design of COA pavements, namely full concrete-asphalt bonding and high LTE, are not realistic. Based on the results of this research, the use of short slabs, around 1.8 m (6 ft) long, is recommended in dry and hot climates.