Mechanical properties of tack coat on asphalt concrete interfaces

Tack coat is often used in the engineering project of new construction and maintenance of asphalt concrete pavements. At present, the relative construction norm of tack coat in Taiwan has neither detailed definition on the breaking time of tack coat material, nor does suggest or restrict to use what kind of tack coat material for different overlay type. Therefore, it's necessary to explore the influence of the type, application rates, curing time of tack coat to utilize on the shear strength of the interface of pavements. This research employs CRS-1, emulsified asphalt of rubber to be tack coat materials, and the direction shear testing apparatus to analyze the influence of tack coat on the engineering properties of the interface of asphalt concrete. The results shows that shear strength of interface is influenced by curing time of tack coat indeed. The breaking time of tack coat was quantified reasonably through the ratio of breaking time or viscousness development of tack coat material. According to the destroy criterion of Mohr-Coulomb, the cohesion of the interface significantly affected by specimen gradation of tack coat. The degree of cohesion of interface among different specimens of tack coat would be dense asphalt-dense asphalt (DA-DA) > porous asphalt-dense asphalt (PA-DA) > porous asphalt-stone mastic asphalt (PA-SMA). There is notable influence of the change of temperature on shear strength and cohesion of interface of asphalt concrete. Higher shear strength and cohesion were observed at low temperatures. The change in temperature had least influence on the shear strength of PA-SMA gradation through the result of test.