Analysis of long-term leachate from pavement constructed with recycled concrete aggregates

The use of recycled concrete aggregates (RCA) in pavement construction offers significant sustainable and economic benefits, including resource conservation and reduced CO₂ emissions. However, the high pH leachate generated by RCAs can become an environmental concern, potentially contaminating surrounding soil and water resources. This study investigates the long-term leaching behavior of RCAs, used in base layer, under field conditions at a road-testing facility in Minnesota. By examining leachate's pH, electrical conductivity, and elemental concentrations, the research identifies key factors affecting leachate chemistry, such as material composition, carbonation effects, and soil interactions. Field data indicates that in-situ carbonation of RCAs leads to a protective layer that mitigates pH levels over time. The study highlights the effectiveness of natural processes in reducing the high pH of RCA leachates and reveals that they do not present a significant risk of heavy metal pollution. Additionally, it also discusses the use of U.S. Environmental Protection Agency (EPA) method 1316 in simulating extreme case scenarios, comparing it with stagnant leaching (EPA 1316 without agitation) test procedure to obtain data that better represents field conditions. The results from stagnant leaching tests were found closer to field representation, given their less aggressive testing approach.