Proposed AASHTO Structural Design Properties for Corrugated Polypropylene Storm Sewer Pipe

Corrugated polypropylene storm sewer pipe has been available on the U.S. market since 2007. The manufacturing process and structural design are similar to the more widely used high-density polyethylene (HDPE) pipe; however, polypropylene has advantages over HDPE in applications that require higher bending resistance and operating temperatures and greater longitudinal beam strength and stress crack resistance. In 2011, ASTM and AASHTO both adopted specifications for corrugated polypropylene pipe materials and products for use in nonpressure surface and subsurface drainage applications. These standards included some requirements for polypropylene material properties related to structural design, such as the minimum initial modulus and long-term creep modulus, but not all parameters required by AASHTO for the structural design of thermoplastic pipe were addressed. This paper presents the test methods and sampling conventions required to arrive at such structural design properties, as well as test results for four candidate polypropylene resins commercially available in the United States. The paper also uses these test results as the basis for proposed structural design properties for polypropylene storm sewer pipe for adoption into the AASHTO Load and Resistance Factor Design (LRFD) Bridge Design Specifications.