Bharat Madras Natarajan, Zoe Kanavas, Morgan Sanger, Jared Rudolph, Jiannan Chen, Tuncer Edil, and Matthew Ginder-Vogel
Recycled Materials Resource Center, FHWA, RMC Research and Education Foundation, and PCA
Base course (Pavements), Chemical properties, Concrete aggregates, Heavy metals, Leachate, Recycled materials, Subgrade materials
Recycled concrete aggregate (RCA) is a high-quality substitute for virgin aggregate as base or subgrade material in pavement construction. However, heavy metal leaching and/or production of high pH leachate are environmental risks commonly associated with the use of RCA. To characterize changes in physical and chemical properties after use, RCA base course and subgrade soil samples were recovered from the Minnesota road research (MnROAD) field site after eight years and compared to the original RCA physical and chemical characteristics. RCA samples were analyzed to determine their mineralogy, carbonate content, acid neutralization capacity (ANC), material pH, and trace element leaching potential. ANC was higher in the recovered RCA and higher for the fine-grained RCA particles than the coarse particles, which was confirmed by extensive carbonation of the fines fractions during field deployment. Material pH of RCA and subgrade soil samples were significantly higher than leachate pH measured in previous and current field investigations of this site, suggesting that conventional laboratory techniques do not represent field conditions and should be modified to better represent field conditions.