Interlayer bonding design of porous asphalt course interface

Interlayer bonding affects performance of asphalt concrete pavements. In order to guarantee good bonding, tack coats are frequently applied at various interfaces. Interlayer bonding design consists in the determination of the optimum tack coat rate and the ASTRA (Ancona Shear Testing Research and Analysis) test method can be used for this purpose. In this study, the tack coat design of the interface between an existing porous asphalt and a newly laid open graded course was developed. In order to check whether the two porous layers are independent or behave as a Twinlay, the drainability of the resulting double-layered system was also investigated. The ASTRA tests showed that acceptable interlayer bonding results can be obtained for each emulsion rate studied but higher tack coat rates mitigate the scatter of the results. In terms of drainability, the porosity of the existing layer does not increase the drainage characteristics of the double-layered system, for each interface treatment considered.