Statistics for superpave hot-mix asphalt construction quality, control/quality assurance data

Asphalt content, air void content, and mat density measurements for Superpave(R) mixes were collected during 1997, 1998, 1999, and 2000 to develop statistics for a statistical quality control/quality assurance program for the Alabama Department of Transportation (DOT). Data were analyzed to determine if accuracy and variability improved and stabilized as contractors accumulated experience with Superpave mixes, to compare contractor and Alabama DOT measurements, and to assess the effects of maximum aggregate size and the design equivalent single-axle load range. Analyses indicated that the accuracy and variability of asphalt content measurements for Superpave mixes remained consistent and comparable to those for Marshall mixes. The variability of air void contents for Superpave mixes stabilized but remained higher than the variability of air void contents for Marshall mixes. The accuracy in achieving target air void contents for Superpave mixes deteriorated and stabilized at values poorer than those achieved for Marshall mixes. The variability of mat density measurements for Superpave mixes decreased and stabilized at values comparable to those achieved for Marshall mixes. The accuracy of mat density measurements for Superpave mixes improved but stabilized at values poorer than those achieved for Marshall mixes. There are significant differences between contractor measurements and Alabama DOT measurements. Asphalt content decreases as design traffic level and maximum aggregate size increase. The level of mat density achieved increases as maximum aggregate size increases.