When a pavement surface becomes heavily deteriorated, the pavement designer can choose from a number of maintenance and rehabilitation alternatives spanning from thin surface-type treatments to more substantial surface renewal programs involving milling an d the placement of a hot-mix asphalt overlay. In the past, thin surface treatments were generally limited to lower volume roads, as ride quality and the existence of loose aggregate prevented its use on higher volume, higher speed facilities. However, th is is no longer the case with the advent of bonded overlay systems, where a spray paver application system enables heavier tack coat application rates to be used in conjunction with aggregates already coated with asphalt. Thin bonded overlay systems, or TBOs, appear to have performance benefits over traditional surface treatments and overlay systems. However, the assessment and, moreover, the quantification of the crack resistance of these thin pavement surface renewal systems presents a significant scientific challenge. The development of such a system is the focus of this paper. Nineteen pavement sections representing five pavement projects, various tack coat application rates and types, asphalt concrete gradations (dense and gap), construction techniques (conventional and spray paver) are evaluated in this study. Core samples from each of the pavement projects were procured and fracture characterization tests were performed using the disk-shaped compact tension fracture test (ASTM D7313-07b) and/or a variation of the test. The test variation, termed the compact tension test, or C(T), is a specifically tailored version of the DC(T) test designed for testing TBOs. The laboratory fracture results obtained from both of these tests demonstrate significantly higher fracture resistance characteristics for gap-graded TBOs as compared to conventionally placed asphalt overlays. This appears to be due to the significant upwards wicking of the heavy tack coat material into the gap graded mix. The dense graded TBOs, which are a relatively new concept, showed fracture energies that were slightly higher than conventionally placed overlays but significantly lower than the gap graded TBOs, probably as a result of the lower amount of upwards wicking of the tack c oat binder as compared to the gap graded system. In order to further explore the cracking resistance of TBOs, a series of numerical simulations were performed to evaluate the relative thermal cracking potential of dense and gap graded TBOs as compared to conventional HMA overlays. The simulation results further reinforce the finding obtained from laboratory fracture testing.
