For many years, the AASHTO Materials Reference Laboratory (AMRL) conducted proficiency sample programs for a variety of tests related to highway materials. Using the data generated in these programs, the appropriate between-lab reproducibility of a specific test was determined. This estimate of variability helped testing labs understand why another lab, such as a state highway agency’s lab, could have a different, and possibly failing, result—even though the original lab’s result passed the specification.
Starting in 1999, Paramount Petroleum Corporation initiated a similar program for roofing asphalt binders based on the tests in ASTM D312, Standard Specification for Asphalt Used in Roofing. In 2005, the Asphalt Institute became involved with the operation of the proficiency sample program. A small fee was established for each set of samples to cover sample preparation, shipping, and reporting.
Participating labs receive two quart containers of roofing asphalt binder and perform a variety of tests specified in ASTM D312 including: Ring and Ball Softening Point (ASTM D36); Cleveland Open Cup Flash Point (ASTM D92); Penetration (ASTM D5) at 32, 77, and 115°F (0, 25, and 46°C); Ductility (ASTM D113); Rotational Viscosity at 400°F (ASTM D4402); and Stain Index (ASTM D2746). Test results are then returned to AI for analysis and generation of a standard report.
The program started by Paramount provided some interesting data regarding the reproducibility of the test results for the participating labs. While the results were generally more variable for all tests than the ASTM d2s limits, the variability was higher for some tests than others. For example, the ASTM d2s limit for the Ring and Ball Softening Point test is 3.5°F. The average d2s limit for softening point for the round-robin programs conducted from 1999 to 2004 was approximately four to five times greater (16.3°F).
Through increased knowledge of testing variability and its causes, the between-lab reproducibility should improve for the common tests for roofing asphalt binders, as well as any future tests that may be used in characterizing the physical properties of roofing asphalts. To this end, the continued success of the Proficiency Sample Program for Roofing Asphalts will play a key role.
For more information or to participate in this program, call Mike Beavin at (859) 288-4973.