Effectiveness of Heavier Tack Coat on Field Performance of Open-Graded Friction Course

Compared with a conventional hot-mix asphalt mixture, an open-graded friction course (OGFC) is more prone to pavement distresses, such as cracking and raveling, which result in a shorter service life. One way to potentially improve the performance of OGFC is to enhance the interface bond between the OGFC and the underlying layer by applying a heavier tack coat. This study evaluated the effectiveness of using a heavier tack coat on the field performance of OGFC by comparing the field performance of the same OGFC mixture with different tack coats placed on Sections N1 and N2 of the National Center for Asphalt Technology pavement test track in Opelika, Alabama. In Section N1, a heavier polymer-modified tack coat was applied with a spray paver immediately before the OGFC layer was placed. In Section N2, a distributor truck applied a trackless tack at a regular application rate. The sections were trafficked to 10 million equivalent single-axle loads by a fleet of heavy trucks for 2 years. The field performance of these two sections was monitored weekly. Field performance characteristics measured included pavement stiffness, pavement structural response, surface functional characteristics, and pavement distresses. The results showed that the OGFC layer in Section N1, in which a heavier tack coat was applied, performed better than that in Section N2, in which a conventional tack coat was used. It is recommended that a heavier tack coat be used to improve the performance of OGFC surfaces.