Time–temperature superposition principle for interlayer shear strength of bituminous pavements

Poor interlayer bonding leads to a reduction in service life of bituminous pavements, thus the identification and measurement of the parameters affecting interlayer shear strength (ISS) are becoming increasingly important. This study focuses on the effects of test temperature and interlayer deformation rate (IDR) on the ISS of double-layered asphalt concrete specimens, with the aim of comparing two different shear testing devices. Specifically, tests were performed by means of Ancona Shear Testing Research and Analysis and Leutner devices, at temperatures ranging from 5°C to 40°C and deformation rates ranging from 1 to 50 mm/min. Moreover, two interface conditions (with and without tack coat) were investigated. Experimental data showed that for both shear testing devices, higher IDR results in higher ISS, because of the time-dependent response of bituminous mixture and that the effect of IDR and temperature on ISS can be superposed allowing a master curve to be satisfactorily obtained using a three-parameter sigmoidal model.