This project assessed the use of crushed fines from recycled\nconcrete (CFRCs), modified with nano silicon dioxide, to passively remove chlorides from polluted stormwater\nrunoff.<\/p>\n\n\n\n
Highway runoff, a major source of non-point source water pollution,\nhas adverse effects on adjacent waters if no measures are taken to remove\nexcessive contaminants that accumulate from highway construction, maintenance,\nand use. Cold climate may present additional challenges. Snowmelt and\nrain-on-snow events can produce large runoff volumes, and frequent salting and\nsanding activities may increase sediment loads. Snow\/ice control products applied\nto winter pavement are significant sources of stormwater pollution. Chloride\nsalts used as freezing point depressants are highly soluble in water and are\ntherefore very difficult to remove from water bodies. They do not degrade in\nthe environment, and their accumulation therefore poses a long-term risk to\ngroundwater quality. <\/p>\n\n\n\n
Transportation agencies need cost-effective tools to address\nthis issue. However, current approaches for treating chloride-laden stormwater\nmainly rely on diversion and dilution rather than on removal of the chlorides. <\/p>\n\n\n\n
To address this issue, this project preliminarily assessed\nthe effectiveness of using crushed fines from recycled concrete (CFRCs), subjected\nto nano-modification, to act as a passive cementitious filter to treat surface stormwater runoff\ncontaining high levels of chlorides and typical levels of total phosphorus,\nnitrogen, and metals. The researchers tested nano silicon dioxide (SiO2<\/sub>)\nas the modifier for the CFRC. Samples of CFRCs were processed by admixing nano\nSiO2<\/sub> at 0.3 percent (by mass), and then the material was heated at\n525\u00baC for 3 hours.<\/p>\n\n\n\n The researchers also sought to determine the mechanisms\nunderlying the engineered sorbents\u2019 removal of contaminants. They characterized\nthe chemical and physical properties of these CFRC materials by applying X-ray\ndiffraction (XRD), Fourier\ntransform infrared spectroscopy (FTIR), Brunauer-Emmett-Teller (BET)\nmeasurement, scanning electron microscopy (SEM), and energy dispersive X-ray\nspectroscopy (EDS). <\/p>\n\n\n\n The modified CFRCs showed good potential to chemically bind chloride. And once saturated with contaminants, these filter media could be fully recycled in sustainable concrete applications. For these reasons, this passive stormwater treatment method could substantially benefit highway and other agencies that must clean stormwater runoff, particularly in cold climates. <\/p>\n\n\n\n