Volume 3, Issue 8 (September 2006)
The Effects of Construction Variability on the Superpave Simple Performance Test
The Superpave Simple Performance Test is quickly coming into the mainstream of practice for research purposes and implementation by owner/agencies. The research presented in this paper focuses on understanding the nuances of the testing procedure and building libraries of values for future reference. This project examined both 12.5-mm and 19.0-mm mixtures from the State of Wisconsin which included various traffic volumes. Of particular importance was construction variability in terms of air voids and asphalt binder content and their impact on performance with the flow number test. Plant produced mix was sampled for the jobs as well as the asphalt binder. Specimens were compacted to 4.0, 7.0, and 10.0% air voids at the sampled asphalt binder content. Additionally, specimens were further mixed with +0.3 % asphalt binder content and compacted to 7.0% air voids. The air voids and asphalt binder content changes were based on the tolerances set by typical construction variability and Wisconsin Department of Transportation specifications, respectively. The testing found that the flow number was greatly affected by air voids, but was rather insensitive to changes in asphalt content and nominal maximum aggregate size. It was determined that the accumulated microstrain at tertiary flow would be a good measure for comparing performance within a specific mixture in terms of changes in air voids and asphalt binder content. The flow number was found to be the best measure for comparing between different mixtures.