Use of raw chat in hma surface-environmental and engineering characterization

Over 35 million cubic meters of chat, a waste material from abandoned lead and zinc mining operations, are presently stockpiled in large piles on the surface of the Tar Creek Superfund Site. Currently, Oklahoma Department of Transportation (ODOT) uses a rather small percentage (about 20%) of washed (not raw) chat. There is a pressing need to significantly increase the use of raw chat in hot mix asphalt (HMA) by the DOTs in the region. Recently, researchers at the University of Oklahoma reported that as much as 50% raw chat can be used safely in an S3-type Superpave base mix. In the present study it has been revealed that as much as 80% raw chat can be used in an S5-type Super-pave surface mix. A relatively small percentage (40%) of raw chat produces high VMA (15% or more), and it increases with an increase in chat percent. Chat-asphalt mixes also did well in performance tests, namely moisture susceptibility, APA rut, and permeability. A suite of environmental tests were performed to examine the leaching potential of heavy metals (lead, zinc, and cadmium) in chat due to dry and wet rut tests, and simulated milling. Tests indicate that chat-asphalt can be used safely as a roadway surface.