Construction and maintenance of roads requires large volume of aggregatesfor use in base or subbase layers. Because of the cost of virgin aggregates, federal and state agencies are encouraging the recycling of waste materials including materials in old pavements. This study evaluated the suitability of fly ash (FA), reclaimed asphalt pavement (RAP), recycled cement material (RCM), and foundry sand (FS) mixed in with virgin aggregates as base and subbase materials. In this paper we report the results on contaminant leaching from six mixtures of FA-RAP-aggregates under saturated and unsaturated conditions. For all six mixtures and virgin aggregates, the concentrations of most inorganic chemicals in both batch and flow thru modes were either below the detection limit of the instrument or less than the EPA drinking water standard. The exceptions were the aluminum, chromium and barium concentrations. Aluminum and chromium concentrations were higher than EPA drinking water standard in both batch and flow-thru tests whereas barium concentration exceeded EPA drinking water standard in batch test only. Aluminum concentrations in the leachate increased with an increase in the proportion of RAP in the mixtures. However, chromium concentration in the leachate increased with an increase in the proportion of FA. It appearsthat up to 5% fly ash and 75% RAP mixed in with virgin aggregates will not lead to any substantial leaching of various inorganic chemicals to the surrounding environment. At 15% FA, there is a slight risk that there may be some transport of dissolved inorganic chemicals at concentrations higher than the EPA drinking water standards. This may not be a problem for ground water contamination because of the presence of additional soil layers below the base and subbase layers. However, there is some risk that these contaminants may show up in surrounding surface waters.
Abstract