Recycled Materials as Substitutes for Virgin Aggregates in Road Construction: II. Inorganic Contaminant Leaching

Construction and maintenance of roads requires large volume of aggregates for use in base or subbase layers. Because of the expense of buying virgin aggregates, federal and state agencies are encouraging the recycling of waste materials in road construction. A study was under taken to evaluate 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 inorganic contaminants leaching from six mixtures of FA-RAP aggregates under batch and flow through conditions. The concentrations of most inorganic chemicals in both batch and flow through modes from all six mixtures were either below the detection limit of the instrument or less than the EPA drinking water standard. The exceptions were Al and Cr. Aluminum concentrations were higher than the EPA secondary drinking water standard in both batch and flow-through tests whereas Cr concentration exceeded the primary EPA drinking water standard in the flow through tests only. Aluminum concentrations in the leachate increased with a decrease in the proportion of FA whereas Cr concentration in the leachate increased with an increase in the proportion of FA in the mixtures. The mixtures had lower pH compared to 100% FA, due to dilution of Ca(HO)(2) in the FA, which resulted in higher Al concentrations. Addition of up to 5% FA and 75% RAP to virgin aggregates does not lead to any substantial leaching of various inorganic chemicals. At 15% FA, there is a slight risk for transport of some dissolved inorganic chemicals at a concentration higher than the EPA primary drinking water standards.