This research evaluated the single-point notched constant tensile load (SP-NCTL) test as a measure of slow crack-growth resistance under sustained loading of high-density polyethylene (HDPE) resins–including postcomsumer resins (PCR)–that are intended for nonpressure drainage pipes. The research was based on both the requirements for minimum slow crack-growth resistance and the results of actual experience.

The Geosynthetic Research Institute (GRI) of Drexel University in Philadelphia, Pennsylvania, was awarded the contract for NCHRP Project 4-24, "HDPE Pipe Material Specifications and Design Requirements," to undertake this research. GRI was assisted in this effort by Simpson Gumpertz & Heger, Inc., of Arlington, Massachusetts.

Research results include recommended modifications to the current AASHTO Standard Specification for Corrugated Polyethylene Pipe-M 294, to the AASHTO Standard Specification for Highway Bridges-Section 18, and to the AASHTO LRFD Bridge Design Specifications. Among the recommended modifications for revisions were revised cell classifications and an additional environmental stress crack-resistance evaluation that incorporate the SP-NCTL test. Research results included recommended minimum failure times for the SP-NCTL test for resin that is used in the manufacture of HDPE drainage pipe. A recommended minimum failure time for the SP-NCTL test was also included for resin that is used to manufacture Types C- and S-helical pipes in order to provide a baseline requirement for accepting possible future overseas HDPE pipe production (this type of pipe is no longer produced in the United States).

Research results stress the necessity of controlling procedures for installing HDPE drainage pipe to control localized overstressing. This research did not investigate smaller-diameter HDPE pipes; therefore, there are no recommendations in the agency final report for pipes that are less than 300 mm thick (AASHTO M 252 Drainage Tubing). Furthermore, it was judged premature to recommend that the SP-NCTL test be used as the Stress Crack Resistance test using coupons from finished HDPE corrugated drainage pipes. Because this is the first major investigative effort designed to relate the results of a crack-resistance index test against the quality of field performance, finer tuning of the minimum slow crack-growth requirements for HDPE resins that are intended for use in HDPE corrugated drainage pipe may occur as the technology matures and as additional observations of field experience are noted.

Status: The agency's final report has been published as NCHRP Report 429, "HDPE Pipe: Recommended Materials Specifications and Design Requirements." The agency report is also available in portable document format (PDF); however, Appendixes A, B, D, E, F, G, and H have not been edited by TRB. Double-click on the files below to access the report. (A free copy of the Adobe Acrobat Reader is available at https://www.adobe.com.) PLEASE NOTE: Due to the very large size of these files, it may take a long time--possibly more than 1 hour collectively--to download. We regret the inconvenience.

NCHRP Report 429, Part A

NCHRP Report 429, Part B