Investigation of the impact of conditions of application of tack coats on the interlayer bond strength

Abstract

An effective and durable bond between the various constituent layers is an absolute prerequisite for the durability of a road pavement. To ensure the adhesion between successive pavement layers, cationic bitumen emulsions are the most frequently used type of tack coats. 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 Belgian Road Research Centre actively participates in a Belgian working group on tack coats initiated by the Walloon federation of road contractors and the Walloon public service. The objective of this joint working group 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 emulsion, spraying equipment, nature and preparation of the binder course, breaking and curing times of the emulsion before overlaying, etc. With a view to this objective, a test site was constructed in the summer of 2014, consisting of four test sections differing in type of tack coat, milling speed and cleaning operation of the binder course. The bond strengths were investigated by direct shear test. This article describes the conditions of application, the measurements made on site (tack coat application rate, binder course texture and cleanliness, etc.) and the results of the interlayer adhesion test performed in the laboratory on specimens taken from the four test sections.