Design, Construction, and Maintenance of Open-Graded Asphalt Friction Courses
Open-graded asphalt friction course (OGFC) is an open-graded Hot Mix Asphalt (HMA) mixture with interconnecting voids that provides improved surface drainage during rainfall. The rainwater drains vertically through the OGFC to an impermeable underlying layer and then laterally to the daylighted edge of the OGFC. In addition to minimizing hydroplaning potential during rainfall and providing improved friction values on wet pavements, the OGFC offers the following advantages compared to other dense-graded surfaces: (a) reduced vehicle splash and spray behind vehicles, (b) enhanced visibility of pavement markings, (c) reduced nighttime surface glare in wet weather, and (d) reduced tire-pavement noise.
Numerous states in the US currently using OGFC have experienced excellent performance in terms of safety (improved surface friction) and durability. The following problems, which were experienced by some states during OGFC trials in the 1970s, have been solved: (a) raveling, (b) delamination, (c) loss of permeability after a few years in service. This has been accomplished by one or more of the following: use of polymer-modified asphalt binders, relatively high asphalt content (by using fibers), and/or relatively open gradations.
Based on the experience of the successful states in the US, experience in several countries in Europe, and the recent National Center for Asphalt Technology (NCAT) research, a mix design method has been developed for a new-generation OGFC. In addition to using polymer-modified asphalt binder and fiber, the new-generation OGFC is highly open-graded with high permeability. The mix design procedure addresses the concerns of the northern tier states with cold climates by including abrasion tests on new and aged mixtures, and subjecting the OGFC mix to freeze and thaw cycles.
The recommendations discussed in this report for materials selection, mix design, construction, pavement structural design, winter maintenance, and rehabilitation should provide the necessary guidance to maximize the potential for OGFC.