Michael Pluimer of Crossroad Engineering Services collects data on the performance of recycled HDPE bellows in southeastern Pennsylvania. | Provided by Advanced Drainage System (ADS).

This article has been corrected.

A group approved the use of recycled HDPE in road drainage pipes, which opened up a potentially huge market for recycled plastics. Officials recently explained the work that pushed this decision.

The American Association of State Highway and Transportation Officials (AASHTO), an organization whose members include the State Department of Transportation (DOT), approved new specifications for high-density polyethylene bellows used under highway and rail lines last year. For decades, the diameter of the black pipe has ranged from 4 inches to 60 inches, and it has been made of virgin plastic in accordance with the specifications.

Recycled HDPE has been used in pipelines to meet the rainwater discharge needs of private properties. The new M 294 R specification removes barriers that prevent DOT from purchasing post-consumer and post-industrial HDPE pipelines for highway projects and other public passage rights.

"We really feel that this will change the rules of the game in the industry and the states because, frankly, this is a more sustainable way of pipe production and manufacturing," said Michael Pluimer, owner and assistant professor of Crossroad Engineering Services. At the University of Minnesota Duluth. "I think the states will benefit a lot from this."

Pluimer spoke at a recent webinar hosted by the Northeast Recycling Council (NERC) and the Association of Plastic Recyclers (APR), where he tested the durability and longevity of recyclable pipes. (APR owns Resource Recycling, Inc., the publisher of Plastics Recycling Update.)

Other speakers include Liz Bedard of APR, Ryan Fragapane of AASHTO and Joe Babcanec of pipeline manufacturer Advanced Drainage Systems (ADS).

Pluimer is involved in research on the durability of recycled HDPE pipes, including his work in a paper published in 2016. The National Cooperative Highway Research Program provided $950,000 to fund two research efforts, and the Southeastern Pennsylvania Transportation Authority sponsored Pluimer, who said the thesis work at Villanova University.

Pluimer said that when it comes to the failure of these rainwater pipes and culverts, the main concern is the rupture that occurs when the pipeline is exposed to low or medium pressure for a long time. In order to test the original plastic pipe, the plastic sample is cut before heating and applying pressure. This process is officially called the cut constant ligament stress (NCLS) test.

However, the test did not provide insight into how pollution affects stress cracking, so they developed a test procedure for unnotched plastic samples called the Unnotched Constant Ligament Stress Test (UCLS). Using this procedure, they tested plastic samples with recycled content under three different conditions: 80 degrees (all temperature degrees Celsius), 650 pounds per square inch (PSI), 80 degrees, 450 PSI, 70 degrees, and 650 PSI.

The data enables Pluimer to develop models of how long different pipelines will be used in the field. Pluimer said the study found that a pipeline with 98% PCR at about 23 degrees at 500 PSI can be used for more than 100 years.

Next, he led experiments to test the accuracy of the mathematical model by exerting tremendous pressure on the recovered HDPE pipes. This work involves two different test methods: using specially designed laboratory equipment to put 1,637 PSI on the pipeline, and bury a section of the pipeline and place concrete blocks on the soil above, resulting in 1,528 PSI. In all cases, when the model indicated that the pipeline would fail, it did happen, and when the model indicated that it would not fail, it did not happen.

"So, basically, we ran a nine-to-nine test on each tested pipeline—it matched our predictions in the model," Pluimer said.

In addition, a three-year study was conducted to evaluate the performance of recycled content pipelines buried only two feet under the rails, he said. The project tested the original and recycled content, and installed meters to record the impact of pressure on the product.

"They performed almost the same throughout the test period," he said.

AASHTO approved and issued the revised M 294 standard in June 2018, allowing the use of recycled HDPE in pipelines. However, the recycled plastic version requires additional regular testing, including oxidation induction time test, elongation at break test and UCLS test developed by Plummer.

AASHTO's National Transportation Product Evaluation Program (NTPEP) audits manufacturers and ensures that required pipeline testing continues. Fragapane, NTPEP's deputy project manager, said that the project auditor inspected the pipeline manufacturer, inspected the paperwork, production line and storage yard. The manufacturer must be able to trace the plastic from the raw material entering the factory to the finished pipe.

The auditor also selects pipe samples to be tested by external laboratories that check carbon content, inner diameter, lining thickness, stiffness/flatness, brittleness, marking, perforation, oxidation induction time, elongation at break, and density melt index. These laboratories also conduct NCLS and UCLS tests, which include applying heat and pressure to see when the plastic breaks. NTPEP puts the test results next to the manufacturer's own test results and shares the data with the state DOT.

Fragapane said that NTPEP issues certification certificates to facilities that produce compliant pipelines. He showed a sample certificate issued to the Advanced Drainage System (ADS).

ADS owns Green Line Polymers, which owns 8 U.S. recycling facilities and processes a total of approximately 255 million pounds of post-consumer HDPE (including used and discarded commercial and industrial products) and 170 million pounds of post-industrial HDPE each year, said ADS National Engineering Project Manager Babcanec.

Babcanec said that ADS estimates that about a quarter of all colored HDPE collected on the roadside in the United States is recycled into ADS drainage products.

Babcanec said that when developing the recycled content of the M 294 pipeline, ADS found that mixing different raw materials is the key to ensuring that the pipeline meets the AASHTO specification, because the post-consumer material itself is quite poor. On the other hand, the post-consumer materials are at least consistent in performance, making it easier for Green Line to successfully formulate blends.

The mixing occurs in two stages, both of which are important for improving the performance of the finished pipe. Green Line performs "salt and pepper mixing", or mechanical mixing of flakes from post-consumer and post-industrial sources. Then, to further homogenize the plastic, Green Line melts it and pelletizes it, Babcanec said. Since PP caps on HDPE bottles are difficult to classify, PP contamination is an important issue. But PP and HDPE melt at different temperatures, which means that Green Line can remove PP before HDPE is pelletized.

Babcanec said that through testing with Battelle's laboratory, ADS has developed an M 294 R pipe consisting of 80.5% recycled HDPE, 15% high molecular weight virgin HDPE and 4.5% additive package. He pointed out that during the NCLS and UCLS tests, high molecular weight HDPE further improved the pipe’s stress crack resistance.

According to the NERC-APR document, the following companies are now producing M 294 pipe with post-consumer HDPE: Advanced Drainage Systems (ADS), Crumpler Plastic Pipe, Fratco, Haviland Drainage Products, Lane Enterprises, Prinsco, and Timewell.

Bedard, APR's Olefin/Rigid Project Director, emphasized the importance of the new specifications to promote domestic demand for recycled HDPE. With the assistance of NERC, APR plans to carry out other activities to support this work, including creating a catalog of pipe manufacturers, publishing case studies, conducting other education and outreach activities, and measuring the market impact of the project.

Babcanec pointed out that the specification allows manufacturers to recycle single-use packaging into durable products with a long life. The product is very suitable for waste because the color does not matter (in any case, it will be dyed black to improve the product's UV resistance) and the smell is not a problem.

Babcanec said: "We are using... single-use plastics, which may have a lifespan of up to six months, and we are actually turning them into products that can be used for more than 100 years." "I think this is something everyone can quote Proud thing."

When asked about the price difference between the new tube and the recycled M 294 tube, Babcanec said that the prices are similar, if not the same. He pointed out that ADS and other manufacturers must conduct more tests on recycled content pipelines. But Babcanec also said that recycled plastics can ensure a stable supply of raw materials, which is important in situations such as Hurricane Harvey, because Hurricane Harvey interrupted the supply of virgin plastics to factories on the Gulf Coast.

Pluimer said he thinks there will be some ups and downs in pricing, but some states are ready to pay more for recycled plastic pipes.

"We see some states wanting or interested in paying a premium for materials made from recycled ingredients, just because it is beneficial from a sustainable development point of view," he said.

This article has been corrected to state that ADS has developed an M 294 R pipeline with a 4.5% additive package. Due to a typographical error, the article previously pointed out the wrong percentage of product additives. 

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