Permeable Friction Course for Sustainable Highways

Abstract

A permeable friction course (PFC) is a 50 mm layer of porous asphalt placed on top of conventional, impermeable pavement. This paper describes a multi-year research effort on the water quality and hydraulic aspects of PFC. Water quality monitoring of three field sites near Austin, Texas showed a 90% reduction of total suspended solids (TSS) compared to conventional pavement. Significant reductions were also observed for total copper, total lead and total zinc, though concentrations of dissolved constituents were not significantly different. The hydraulic properties of PFC are of interest to assess the drainage capacity of the pavement and the effects of clogging. The properties investigated in this study were the porosity and the hydraulic conductivity. Porosity was measured from core specimens and found to range from 0.12 to 0.23. Hydraulic conductivity was also measured from core specimens and ranged from 0.1 to 3 cm/s. A new field method for measuring the in-situ hydraulic conductivity of PFC was developed and compared to the laboratory measurements. Predictions of the water depth on PFC roads are needed to assist designers in selecting a pavement thickness and to evaluate the effects of clogging. A Permeable Friction Course Drainage Code (PERFCODE) was developed to make these predictions. Measured porosities and hydraulic conductivities were used as inputs to PERFCODE. Outputs were the variation of water depth through a storm and the runoff hydrograph. The modeled hydrograph is compared to runoff hydrographs obtained by field measurement.