Comparisons of Contractor and State Transportation Agency Quality Assurance Test Results on Mat Density of Hot-Mix Asphalt Concrete

A typical component of highway construction quality assurance programs 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 on in-place properties of hot-mix asphalt are increasingly used in the acceptance decision in many states. Results of tests performed by contractors and state departments of transportation (DOTs) in North Carolina, Florida, and Kansas consistently indicate that differences between contractors and state DOT test results for hot-mix asphalt concrete mat density are statistically significant. Furthermore, these comparisons consistently indicate less variable and more favorable contractor test results, relative to specification limits, that give more favorable acceptance outcomes. Details of quality assurance processes (sampling and testing frequencies, test methods, verification procedures, and acceptance procedures) appear to have little if any effect on these comparisons. These findings provide information for state DOTs to consider in structuring their quality assurance programs, specifically the role of contractor-performed tests in acceptance decisions.