Developing a Method for Testing Tackiness of Bituminous Tack Coats

In the construction of roads, asphalt is paved in individual layers. To ensure that these layers behave as a single, cohesive unit, a bituminous tack coat is applied between layers. It is critical that this tack coat is adhesive when the hot mix asphalt is applied and non-adhesive otherwise. As of present, there is no standard method for testing the adhesion of bituminous tack coats. A procedure was developed such that a sample tack coat of ~1 mm thickness was allowed to adhere to a temperature-controlled lower plate. After a set time, the upper geometry was lowered until a set normal force was achieved. After a short adhesion period, the upper geometry was raised as a controlled, constant rate such that a plot of the resulting normal force over deformation could be generated. The area beneath the resulting curve was determined to be the pull-off work necessary for contact between the upper geometry and the tack coat to be broken. Using this method, two asphalt bases were tested with incremental increases in additive to empirically determine the relative tackiness of each sample. By this method, the bases and their modifications could be ranked qualitatively in terms of tackiness for easy reference.