Impact of tack coat application conditions on the interlayer bond strength

Abstract

The intrinsic characteristics of tack coats play an important role in the adhesion between layers, but the conditions of application of these coats are equally crucial. In this context, the BRRC actively participates in a Belgian working group on tack coats and the objective is to carry out a “field” study about adhesion between layers while evaluating the influence of different parameters– such as type and rate of spread of tack coat, nature and preparation of the binder course, etc. With a view to this objective, a test site was constructed consisting of four test sections differing in type of tack coat, texture due to milling speed and cleaning operation of the binder course. The bond strengths were investigated by direct shear tests performed in the laboratory on specimens taken from the four test sections. This paper describes the conditions of application, the measurements made on site and the results of the interlayer adhesion test. The test sections were constructed in good conditions, leading to high shear strength values. Only the effect of tack coat type could be demonstrated, while for all milling speeds and cleaning operations considered in this study, the results were equally good and not significantly different.