A good inter layer adhesion is essential for a good performance of asphalt concrete roads. The empirical use of tack coats serves this goal. A parameter study should provide information for a more systematic use. Parameters like surface characteristics, cleanness, type of pavement, being of the practical importance, are investigated.
The aim of the research project is the evaluation of an appropriate testing scheme to asses tack coats (applicable type) and criteria for application (dosage, surface properties, and others). The project deals with new and used surfaces as well as surfaces after removal of upper layers. The project will proved a base for standardisation, thus contributing to a prolonged use of roads.
A basis for determining the quality of the layered composite is the shearing test according Leutner, where at selected systems but also the suitability of the strength tester is to be clarified. In some specimens, the water storage is carried out in order to discuss the influence of moisture on the coating adhesion. The long-term effects, that is e.g. the temporal variation of adhesion (setting process or building a adhesion effect under load) are considered in more detail in the system.
In road construction tack coats have been used for many years to improve the adhesion between the different layers of a pavement. Although the benefit of using a tack coats is not debated, it is not clear how much tack coats effectively contribute to the adhesion properties.
To evaluate the limits of the application of tack coats dirt and moisture was applied between the two layers before and after the application of a tack coat. For comparison the tack coat was applied on one side of the specimen only, when the other stayed untreated.
Besides, the influence of tack coats on fine milled surfaces and the influence of curing time on the adhesion were also investigated.
It could be shown that especially in the case of dirt and moisture – common phenomena on construction sites - tack coats have a great potential to secure and improve adhesion properties. When – in case of “no tack coat” - the cores already broke during coring, the cores with tack coat achieved shear forces up to 10kN. Furthermore, there is a great difference if the tack coat is applied before or after the dirt/moisture treatment.
As opposed to the benefit of tack coats on dirty and wet surfaces the advantage of tack coats on fine milled surfaces is doubtable. Also the use of polymer modified tack coats seems not to be beneficial when the pavement is constructed using ordinary e.g. non polymer modified binder.