Evaluation of Bonding between HMA Layers Produced with Different Tack Coat Application Rates using Shear-type and Tension-type Tests

摘要

Bonding between adjacent pavement layers is one of the most important factors affecting overlayservice life. Poor bonding between adjacent layers of hot mix asphalt can lead to different typesof distresses in pavement system such as slippage cracking, top-down cracking, prematurefatigue, and in some cases complete delamination. Despite the importance of interface behaviorbetween different pavement layers, there is no consensus as to the best bond testing technique.In most cases, interface bonding is assessed in terms of shear strength. Considering that interfacedebonding can be caused by both shear and tension loading, and that the optimum tack coatobtained from shear-type and tension-type interface tests may be different, a study to compareshear versus tension testing results was conceived and carried out. Optimum tack coat rates asobtained from shear-type and tension-type interface tests were obtained and compared. It wasfound that a significantly higher tack coat rate is needed to create a strong adhesive bondbetween layers as compared to the optimum rate suggested by shear type tests. In addition, shearand tension tests produced difference rankings in tack coat types in terms of their expectedperformance under shearing and tensile forces, respectively. It is recommended that tension-typetests such as Interface Bond Test (IBT) be used along with shear-type tests in the design andcontrol of tack coats and thin-bonded overlay systems and that additional studies be performed todevelop a system that allows the holistic optimization of pavement bond on the basis of meetingfunctional requirements in both shear and tension for a given pavement system, traffic level, andenvironment.