Hydraulic and environmental compatibility of RCA with filters and subgrades in highways

Recycled concrete aggregate (RCA) has great potential to be a replacement for virgin aggregate in the base layers of pavement structures as an unbound granular material. RCA is favourable in these applications; however, its environmental suitability and hydraulic compatibility with underlying filter geotextiles need to be investigated before a design. This study evaluated an RCA from a road construction site in Maryland, USA, for leaching properties to ensure that the leachate satisfied the water quality limits (WQLs). Sequential-column leach tests were set up with a common subgrade material to simulate the effect of a subsoil on leachate concentrations. Once the leachate had passed through the subgrade soil, only copper was found to have stable leachate concentrations exceeding the US Environmental Protection Agency WQL. Numerical analysis used to model the transport of contaminants through the subsurface to a body of water showed that little to no detectable contaminants reached the surface water even if the body of water was located directly adjacent to the RCA. Long-term filtration tests were performed to evaluate the hydraulic compatibility of RCA with various filter geotextiles placed under RCA in a typical highway system. None of the geotextile–soil systems showed signs of physical clogging, and all were deemed compatible.