Quality Assurance of Mix Properties of Hot-Mix Asphalt Concrete: Multistate Analysis Comparing Contractor and State Transportation Agency Test Results

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. Results of contractor-performed tests of mix properties of hot-mix asphalt (HMA) concrete are increasingly used in the acceptance decision by many state departments of transportation (DOTs). Results of tests performed by contractors and state DOTs in Florida, North Carolina, and California consistently indicate that differences between contractors and state DOT test results for HMA concrete are statistically significant for most mix properties. 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, verification procedures, and acceptance procedures) seem to have little, if any, effect on comparisons. Those findings provide information for state DOTs to consider in structuring their quality assurance programs, specifically the use of contractor-performed tests for acceptance decisions.