Developing a Durable Alternative Friction Course for the Suburban Environment in Florida

Abstract

The open-graded friction course, called FC-5, is widely used in Florida to enhance safety. However, the FC-5 layers on suburban roads are prone to premature raveling as a result of increased lateral stresses from turning, braking, and rapid acceleration. This study, therefore, aimed to develop a more durable alternative friction course (AFC) for suburban roads that would have minimal impact on permeability and surface friction. The AFC mixture was designed based on the FC-5 and 12.5 mm stone matrix asphalt (SMA) mixtures. Specifically, the gradation of AFC was designed to be finer than the FC-5 to improve durability but coarser than the SMA to ensure permeability. All three mixtures (FC-5, AFC, and 12.5 mm SMA) were prepared with two aggregate types (limestone and granite) and two asphalt binders (PG 76-22 and high polymer modified binder). Laboratory tests, including the Cantabro, Hamburg wheel tracking, overlay, Florida permeability, outflow meter, circular track meter, and dynamic friction tests, were performed to comprehensively evaluate the durability and functionality of the three mixtures. The laboratory results showed that AFC mixtures demonstrated better friction, durability, and resistance to cracking, rutting, weathering, and moisture damage than FC-5 mixtures while maintaining adequate permeability and drainability. Notably, AFC mixtures showed comparable durability and cracking resistance to SMA mixtures. Based on these laboratory findings, the preliminary AFC design requirements were proposed, including a gradation band, an air void range of 10% to 15%, and a maximum Cantabro loss of 10%.