Methodology to evaluate hydraulic compatibility of geotextile and RCA in underdrain systems

Long-term filtration tests were conducted to assess the hydraulic compatibility of the recycled concrete aggregate (RCA) and nonwoven geotextile that is typically used in underdrains. The RCA samples used in this study were collected from a single facility, but with different ages (aged in the laboratory). Geotextile samples were also exhumed after each test and evaluated for reduction in their serviceability. The laboratory tests showed that aging does not adversely affect the hydraulic properties of the RCA in long-term filtration tests. The results showed that the previously defined serviceability criteria based on gradient and permeability ratios are not relevant to evaluate the hydraulic compatibility of RCA/geotextile tested in this study due to the existence of turbulent flow regime. An alternative limiting ratio called herein hydraulic conductivity ratio (HCRLFT) is proposed and validated with long-term filtration tests performed with natural aggregates. An acceptance criterion of HCRLFT ≤ 4 is suggested to assess the compatibility of RCA (or natural aggregate)/nonwoven geotextile systems.