Performance and Maintenance of Permeable Friction Courses
Burns Dennis Cooley, Inc.
L. Allen Cooley, Jr.
Permeable friction courses (PFC), which include new generation open-graded friction courses, asphalt-rubber friction courses, and porous European mixes (PEM), have gained wide acceptance throughout the southern and western portions of the United States. PFC mixtures are rapidly gaining popularity due to their ability to reduce hydroplaning, splash and spray, and pavement noise, and to improve ride quality and the visibility of pavement markings in wet weather.
There are numerous differences between PFC and the first generation open-graded friction courses (OGFC) widely introduced in the 1970s. PFC typically contains at least 20 percent more asphalt binder (by volume) than conventional OGFC. PFC is generally designed to have at least 18 percent air voids, whereas conventional OGFC mixtures typically contained between 10 and 15 percent air voids. The void structure of PFC allows the mix to be more permeable than conventional OGFC and less likely to trap water that could freeze. PFC--unlike conventional OGFC mixes--may contain fibers, polymer modifiers, or asphalt-rubber, alone or in combination. PFC mixtures are typically placed in thicker layers than conventional OGFC (1.0 to 2.0 inches as opposed to 1.0 inch or less). The thicker, more open matrix allows PFC to drain larger volumes of water off the roadway faster than conventional OGFC and keeps the void structure clean through the flushing action of high-speed traffic, therefore reducing the potential for loss of permeability over time.
All these differences have contributed to a longer reported performance life for PFC compared with conventional OGFC. Research on PFC indicates that the mixes typically last between 10 to 14 years, significantly longer than the first generation OGFC mixtures, which typically lasted between 5 and 7 years. No widespread performance problems such as raveling have been reported with PFC, but concerns remain whether PFC mixes will experience the same performance problems that plagued the first generation OGFC mixes used in freeze-thaw environments. In these environments, the benefits of PFC have generally been perceived to be outweighed by the associated inconveniences and increased cost of winter maintenance and the possible related formation of glaze ("black ice"). While black ice can form on any pavement under the right environmental conditions, there is anecdotal information that it is likely to form earlier on PFC and last longer than it does on other hot mix asphalt surfaces. These concerns are a likely reason that PFC mixes are used predominately in warmer climates found in the southern and western regions of the United States and are not used widely in areas that experience frequent freeze-thaw cycles. Pavement maintenance issues and snow and ice removal are also often cited as obstacles to further increased use of PFC in colder climates.
The objective of this project was to recommend design, construction, and maintenance guidelines that maximize the advantages and minimize the disadvantages associated with PFC use.