Equivalency evaluation of asphalt-based barriers for waste containment

Waste containment and isolation of contaminated sites are critical to the protection of human health and the environment. The US EPA Resource Conservation and Recovery Act provides regulatory standards for containment systems including composite barriers for liner and cover systems. US EPA prescribed subtitle-D composite barrier consists of 1.5 mm HDPE geomembrane (GM) underlain by 60 cm thick compacted clay liner (CCL). In this research, an alternate barrier technology is proposed that incorporates 2 to 3 mm thick fluid applied asphalt/geotextile (FAA/GT) underlain by 10 to 15 cm asphalt concrete (AC) liner.; The objective of this research was to document the technical equivalency between an asphalt composite barrier consisting of FAA/GT-AC and a prescriptive barrier consisting of GM-CCL. A test pad consisting of 2 to 3 mm thick FAA/GT and 10 to 15 cm thick asphalt concrete was designed, constructed using full-scale asphalt paving equipment and its performance monitored. The in-situ hydraulic conductivity of the barrier measured using sealed, double-ring infiltrometer was 1x10-9 cm/s. The laboratory measured hydraulic conductivity of the specimens sampled immediately after compaction was 1x10-10 to 1x10-11 cm/s. The hydraulic conductivities of the same specimens were reevaluated twice after exposing them to the ambient temperature in the laboratory for a period of up to three years. No change in hydraulic conductivity was observed during this period. Beams of aged asphalt concrete were subjected to three-point bending to impart distortions in the range from 1/500 to 1/25. Though observable cracks were developed in the beam that underwent the maximum distortion of 1/25, there was no appreciable effect on the hydraulic conductivity. Average shear strength and average secant modulus of asphalt concrete specimens measured in unconfined compression tests and beam single shear tests were 1070 kPa and 66 MPa, and 970 kPa and 34 MPa respectively. Chemical compatibility of asphalt concrete specimens with broad range of liquids for a period of two years showed good resistance against chemical constituent leachates. The tests on FAA/GT indicated that it can provide effective barriers to liquid and gas migration of water and aqueous solutions, and to other organic solvents when backed up with a thicker layer of asphalt concrete.; Based on the data obtained from the field and laboratory tests, and literature information, a comprehensive equivalency evaluation incorporating hydraulic, physical/mechanical, and construction issues was documented. The evaluation showed that the asphalt composite is superior to the prescriptive barrier in terms of construction, physical/mechanical and hydraulic issues. The equivalency evaluation tabulated for cover and liner applications will enable owners, designers, contractors and regulators to compare asphalt barriers as an alternative to prescriptive subtitle-D barriers.