Transport and retention of water and salt within pervious concrete pavements subjected to freezing and sand application

Pervious concrete pavement can effectively reduce both the volume of water and the concentration of many sediment-associated contaminants in urban runoff. However, chloride from road salt is recognized as a threat to surface and groundwater resources because it is a conservative ion and does not readily bind to soil particles. To better understand and manage water resources in urban environments experiencing annual freeze-thaw cycles, this study examines the impact of road salt (sodium chloride) and sand applications on water and chloride movement in pervious concrete structures in a laboratory setting. Water movement and salt retention were characterized within pervious concrete slabs under frozen and thawed conditions. Laboratory experiments were repeated using both brine (23% salt solution) and fresh water as well as varying additions of sand (typical of winter sand application rates in Canada) to provide a range of temperatures experienced in cold-climate urban environments. Performance testing (via infiltration capacity) was conducted to assess the suitability of pervious concrete in climates where road sand and salt application is necessary. For all experimental conditions studied, chloride was rapidly transported through the pervious concrete. The complete freezing of pore water throughout the concrete slab reduced water and salt movement within the concrete matrix, while sand application reduced water movement through pores and delayed peak flow. The infiltration capacity of the pervious concrete structures, as tested, exceeds the probable maximum water loading rate that will be encountered in Southern Ontario, Canada, with or without sand, frozen or unfrozen. From a groundwater management and source water protection perspective, the data indicate that pervious concrete pavement structures may contribute to chloride contamination of groundwater if used in salt vulnerable areas and groundwater recharge zones.