Field Performance of Corrugated Pipe Manufactured with Recycled Polyethylene Content (2018)

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78 This research project involved an evaluation of the field performance of corrugated HDPE pipes manufactured with recycled materials and the development of proposed criteria for AASHTO materials and design standards based on the research. The key outcome of the research project was the development of a performance-based specification for pipes manufactured with recycled materials that was validated on full-scale pipes in both the field and the laboratory. Some con- clusions of the research project are detailed in the following paragraphs. A new test method—the UCLS test—was used to assess the performance of corrugated HDPE pipes manufactured with recycled materials relative to both the crack initiation and crack propagation phases of the slow crack growth mechanism, and a service life prediction model was proposed based on this test method. The UCLS test was standardized and published as ASTM F3181 and is available for reference in appropriate AASHTO standards. To validate the UCLS-based service life prediction model, full-scale pipes were evaluated in both the laboratory and simulated field conditions. The pipes were installed in highly deflected conditions both in the laboratory and the simulated field test to accelerate failures. Specifically, test pipes were deflected until the vertical inside diameter was reduced by 20% in a parallel plate test in the laboratory, resulting in peak tensile strains of around 3.75% in the pipe wall. Similarly, pipes were installed with loosely compacted ASTM Class III backfill materials inside fabricated precast reinforced concrete chambers to a simulated burial depth of 30 ft, resulting in vertical deflections of around 12% to 15%. Peak local tensile wall strains were calculated to be 3.5%, similar to that observed in the parallel plate test in the laboratory. In the parallel plate test, one of the three test pipes was predicted to develop brittle cracks within a year of test- ing based on the UCLS service life prediction model. In the simulated field test, four of the seven test pipes were predicted to crack. In each case, the pipes predicted to crack developed brittle cracks within the predicted time frame, while the ones that were not predicted to crack did not. Furthermore, it was shown that the service life prediction model based on UCLS testing of coupons of pipe at elevated temperatures provided a very good estimate of the service life of full-scale pipes in actual field conditions. Based on these results, the service life prediction model was validated, and it was concluded that the UCLS test provides the basis for a true performance-based test that can be used to accurately predict the service life of cor- rugated HDPE pipes manufactured with recycled materials. To evaluate the field performance of corrugated HDPE pipes manufactured with PCR materials relative to fatigue from live loads, two 750 mm (30 in.) diameter pipes—one manufactured with 49% PCR materials and the other manu- factured with 0% PCR materials—were installed underneath an active commuter railroad north of Philadelphia. This is the first reported installation of a large-diameter pipe manu- factured with recycled content underneath an active railroad in the world. To amplify live loads, the pipes were installed with just 0.6 m (2 ft) of cover from the top of the pipe to the bottom of the railroad tie. Wall strains and deflections were monitored over 3 years of service, and a laboratory fatigue test was developed to evaluate the pipes’ performance rela- tive to cyclical live loads. Test specimens taken directly from the walls of the pipes were tested for up to 10 million cycles with no failures. Additionally, there were no significant differ- ences in performance observed between the two field pipes. Based on this, it was concluded that fatigue due to live loads in both highway and rail is not a concern for pipes manufactured with or without recycled materials. Revisions were proposed to AASHTO M 294 to incorporate manufacturing and performance criteria for pipes containing recycled materials. The proposed revisions included mini- mum UCLS test requirements for pipes manufactured with recycled materials, providing the basis for a true performance- based specification. A single-point UCLS test conducted at the 80°C/4.48 MPa (650 psi) test condition was proposed as a qual- ity assurance test. For pipes in 100-year service applications C H A P T E R 4 Summary and Conclusions

79 with a design stress of 3.4 MPa (500 psi) and temperature of 23°C, the minimum required single-point UCLS test value is 34 hours. The specification also provides guidance for deter- mining minimum UCLS criteria to ensure the desired ser- vice life at other design conditions. In addition to the UCLS test requirements, an OIT test requirement of 20 minutes, a break strain requirement of 150% and an NCLS requirement of 24 hours were also proposed for inclusion into M 294 for pipes manufactured with recycled materials. A Standard Rec- ommended Practice was developed for predicting the service life of corrugated HDPE pipes manufactured with recycled materials, and design guidelines for thermoplastic pipe were established for incorporation into Section 12 of the AASHTO LRFD Design Specification. This research showed that corrugated HDPE pipes can be successfully manufactured with recycled materials to meet the service life requirements for highway and railroad appli- cations, provided the minimum UCLS performance require- ments established in this research project are met. This groundbreaking study resulted in a true performance-based specification that was validated on full-scale pipes in both the field and the laboratory.