The BFF Test: An Un-Notched Stress Crack Test for Evaluating Resin Blends Containing Recycled HDPE for Use in Corrugated Drainage Pipe

Session 3B
3:30

Richard Thomas and David Cuttino
TRI/Environmental, Inc.

The BFF test is an un-notched, constant load, stress crack test performed at elevated temperatures (70 or 80ºC) in deionized water. The test is a combination of the BAM test, developed in Germany in the early 1990s, the Florida Department of Transportation protocol for 100 year service lifetimes, and uses a dumb bell shaped test specimen with Fat Heads. The test was first used in these laboratories for a commercial client, but was further developed as part of the National Co-Operative Highway Research Program under Project 04-32.

A test specimen is held at temperature under load until a stress crack is formed and grows enough to cause a separation in the specimen. The crack is always initiated at the largest flaw in the test specimen. Examination of the fractured surface microscopically often shows exactly where the crack initiated. The test can be used either as a quality control/quality assurance test or as a tool for estimating the service lifetime of materials that fail by stress cracking. It is particularly suited for resin blends containing post-consumer recycled HDPE because it is sensitive to contamination that may be present in the recycled resin. The test results are also affected by the inherent stress crack resistance of the base resins. More resistant resins can accommodate larger defects before crack initiation occurs.

This paper will describe the test in detail and present selected results from the NCHRP project. The results will be compared to conventional notched stress crack tests and examples of its use for predicting service lifetimes will be presented.