Assessment of Winter Maintenance of Porous Asphalt and Its Function for Chloride Source Control

This study presents the findings from research conducted at the University of New Hampshire Stormwater Center (UNHSC) which investigated porous pavements as a potential strategy for minimizing the use of deicing chemicals for winter maintenance. In cold regions, chloride is an integral component of winter maintenance and safe usage of transportation surfaces. Chloride-laden runoff from impervious surfaces threatens aquatic habitats, degrades drinking water supplies, and corrodes infrastructure. State and federal environmental agencies are beginning to regulate chloride usage through the implementation of total maximum daily loads (TMDLs). Parking surfaces in some watershed studies have been shown to be the single largest chloride source in storm-water runoff, in some instances contributing up to 50% of the total load. This study examined winter maintenance over two winters and 38 storms from 2006–2008. The study evaluated winter performance in response to deicing practices by measuring skid resistance, the degree of snow and ice cover, recoverable chloride mass, and effective salt loads. During and just after snowstorms, analysis of snow/ice cover and pavement skid resistance demonstrated that from 64 to 77% less salt was needed in order for a porous asphalt (PA) lot to maintain equivalent or better surface conditions as compared to a reference dense-mix asphalt (DMA) lot. Between snow storms, the lack of standing water on porous asphalt greatly reduced the frequency and mass of salt applications needed to control black ice. Although the DMA lot received a typical salt application that was four times greater, the annual median snow and ice surface cover for the PA lot was not significantly different ($p=0.749$, 95% confidence), and the annual median weighted skid resistance for the PA lot was 12% greater ($p=0.061$, 95% confidence). A companion study on the hydrologic and water quality performance reported that freeze-thaw was limited due to the well-drained nature designed into the system, and surface infiltration capacities remained in excess of $500\mathrm{cm}/\mathrm{h}$ ($200\mathrm{in.}/\mathrm{h}$), despite the fact that the maximum frost penetration depth observed was nearly 71 cm (28 in.). Porous pavements present one viable potential strategy for chloride reduction.