Quality assurance of hot-mix asphalt - Comparison of contractor quality control and Georgia Department of Transportation Data

Quality assurance is the process by which highway construction elements are sampled and tested to ensure compliance with specifications and other project requirements. The results of contractor-performed tests, originally performed for quality control purposes, are increasingly used in the acceptance decision in many states. The Georgia Department of Transportation (GDOT) uses contractor-performed tests in the acceptance decision on acceptable corroboration of GDOT-performed tests. Statistical analyses were performed to assess differences between tests conducted on hot-mix asphalt concrete by GDOT and its contractors during the 2003 construction season. Measurements of gradation and asphalt content taken by both parties were compared both across all projects and on a project-by-project basis for projects large enough to meet sample size requirements for this type of analysis. Both tabular and graphic representations of data are used to interpret the results. Statistically significant differences occur in some cases; these differences are much more common when comparing variability of these measurements than with the means. At the project level, on most projects in which statistically significant differences occur, the GDOT value typically is larger.