Developing In-Situ Permeability and Air Voids Requirements for Open-Graded Friction Course Pavement: Case Study

Open-graded friction course (OGFC) is a functional mixture used in high-intensity rainfall areas where there exists a risk of flash flooding. To ensure its functionality, there is a need to specify the minimum volumetric requirements on the OGFC mixture. This study aimed at developing in-situ permeability and interconnected air voids content requirements for an OGFC pavement under various rainfall intensities. Seven air voids contents (16%, 17%, 18%, 19%, 20%, 21%, and 22%) of OGFC slab specimens were prepared in the laboratory, and volumetric properties (interconnected air voids and total air voids content) and hydraulic conductivities (permeability coefficient) were characterized. A rainfall simulator was developed to quantify the ultimate drainage capacities of OGFC mixtures under simulated rainfall events. It was found that the OGFC mixture with a higher designed air voids content exhibited a higher permeability coefficient and ultimate drainage capacity. However, the in-situ drainage capacity of an OGFC pavement was affected by the number and width of lanes. Based on a field project that was two-way eight-lane, 2% cross slope, 20% air voids content, and 5-cm thick OGFC, the minimum in-situ permeability coefficient was determined as 825 mL/15 s. It was recommended to integrate design factors such as number and width lanes, and local rainfall intensity into the OGFC pavement design process to achieve desirable in-situ drainage functionality.