Synthesis of Current Practice on the Design, Construction, and Maintenance of Porous Friction Courses

Open-graded friction courses (OGFC), or porous friction courses (PFC) as defined by the Texas Department of Transportation (TxDOT), are a special gap-graded asphalt mixture characterized by a large interconnected air void content. In general, the voids content is at a minimum of 18 percent. Similar mixtures (porous asphalt [PA]) with voids contents as high as 25 percent are successfully applied in Europe. These interconnected voids make these mixtures highly permeable with the capacity to reduce tire-pavement noise. These characteristics are associated with the following advantages that can be obtained from the use of PFC as a surface layer: safety improvements, economic benefits, and environmental benefits. On the other hand, the following aspects are identified as disadvantages of PFC: reduced performance, high construction costs, winter maintenance issues, and limited structural contribution. Substantial efforts have been undertaken to correct previous failures in OGFC, and significant advances have been made since the 1990s with respect to mixture performance of service life. This report summarizes the current state of the practice related to mixture design methods (proposed by different U.S. and international agencies and institutions), construction, maintenance, and performance of surface courses using OGFC and PA identified from a worldwide literature review. In addition, the report presents a synthesis of the relevant aspects related to the current practice and application of PFC in Texas based on the interviews conducted with selected TxDOT districts. The report represents the baseline for a research project aimed to improve the PFC mixture design method using advanced research tools and develop guidelines for construction and maintenance of PFC. In this project, special efforts will be directed to address functionality in terms of permeability and noise reduction, and durability in terms of moisture damage and aging potential.