Plastic Pipes Conference Association # 2023 Lake Buena Vista
Michael Pluimer, Christian Herrild, Patrick Vibien
With enhanced interest in a circular economy and the potential use of recycled HDPE within HDPE conduit, a research project was undertaken to investigate the necessary technical requirements when using recycled HDPE.
High Density Polyethylene (HDPE) conduit is a durable product designed to protect cables buried underground or encased in concrete. Although not subject to long term internal pressure as is seen in water and gas piping, HDPE conduit is subject to coiling and installation stresses and in-service stresses generated from installed curvature, soil loading, rock impingement, etc. These stresses typically do not generate ductile failure; however, they can produce brittle failures if the HDPE material is not sufficiently resistant to this failure mode. The North American conduit industry has long-standing material requirements, including a requirement for Environmental Stress Crack Resistance (ESCR) that has served the industry well and has resulted in few, if any, brittle failures in service.
Using recycled material (post-consumer, post-industrial, post-commercial) introduces the possibility of incompatible contamination that could initiate cracking within the wall. The North American HDPE corrugated pipe industry has already proven the concept and implemented the use of recycled materials. This was done through extensive research and establishing new requirements, based on the ASTM F3181 Standard Test Method for The Un-notched, Constant Ligament Stress Crack Test (UCLS) for HDPE Materials Containing Post-Consumer Recycled HDPE (UCLS) test that assesses the final compound’s resistance to brittle cracking.
As the physical form, installation methods, and in-service requirements for conduit and corrugated drainage pipe differ significantly, a technical assessment of the requirements for HDPE conduit was undertaken. The assessment includes product packaging, storage, installation, and in-service application needs. In particular, the assessment focused on coiling, in-service temperature, and soil loading effects.
This paper provides the results of the technical assessment. Potential requirements in consideration of the applications are discussed and the results of initial testing of blends containing recycle are presented. The recycled blends included both reprocessed pelletized Post-Industrial Recycled (PIR) materials as well as reprocessed pelletized Post-Consumer Recycled (PCR) materials, and they were formulated to meet the baseline requirements and cell classification of the current conduit standards in North America. The recycled content of the finished blends ranged from 30% - 70%. The recycled materials were supplied by various commercial suppliers in North America, and the minimum ASTM D3350 cell classification of the recycled material was 324220B.
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