Open-Graded Friction Courses Suitable for Suburban Environments

Abstract

The Florida Department of Transportation (FDOT) utilizes an open-graded friction course (OGFC), called FC-5, on all multi-lane roadways with a design speed of 50 mph or greater, except for curb and gutter sections, to enhance safety by minimizing hydroplaning. However, FC-5 layers on high-speed multi-lane suburban roadways experience premature raveling due to high lateral stresses caused by turning, rapid acceleration, and braking activities. Currently, the FC-5 mixture is designed with a 12.5-mm nominal maximum aggregate size (NMAS) gradation and a polymermodified PG 76-22 binder. To improve the durability of the FC-5 mixtures, 9.5 mm NMAS gradation and high polymer modified (HP) binder were evaluated. Besides, an alternative friction course was developed which is more durable in suburban environments and is drainable while maintaining adequate friction and texture properties. The experimental plan included four mix designs (FC-5, 9.5 mm OGFC, 12.5 mm SMA, and an alternative friction course), designed with two aggregate types (granite GRN and limestone LMS), and two binder types (PG 76-22 and HP). The laboratory tests included the Cantabro test, Permeability test, Drainability test, Circular Track Meter (CTM) test, Dynamic Friction Test (DFT), Overlay Test (OT), and Hamburg Wheel Tracking Test (HWTT), which characterized the mixture’s durability, permeability, drainability, texture, friction, cracking resistance, and rutting resistance, respectively. Note that the Cantabro and OT specimens were tested both before and after conditioning at the NCAT Accelerated Weathering System (NAWS) to evaluate the aging resistance of the mixtures. The results show that using HP significantly improved the durability and cracking resistance of the asphalt mixture while maintaining permeability, drainability, rutting resistance, macrotexture, and friction resistance. Mixtures with HP showed higher aging resistance compared to those designed with PG 76-22. Using the finer gradation of 9.5 mm NMAS also improved the performance of the FC-5 mixture, but the improvement was generally not significant. The alternative friction course enhanced FC-5 performance, especially with durability. Although the mixture had lower permeability and drainability than that of the OGFC mixture, it was significantly higher than that of 12.5 mm SMA mixtures, indicating its permeable ability. Additionally, the alternative friction courses generally demonstrated higher aging resistance compared to FC-5 and 9.5 mm OGFC mixtures.