Impacts of Ignition Furnace Correction Factor Errors on Quality Assurance of Asphalt Mixtures

Abstract

The accurate determination of asphalt content has long been a key component of assessing the quality and characteristics of an asphalt mixture, with the ignition method (AASHTO T 308) being the most common. Despite previous research work recommending the use of unique correction factors for each mixture and oven, the practice of sharing correction factors is very prevalent. A unique dataset of correction factors and ignition furnace results generated by Maine Department of Transportation (MaineDOT) is analyzed to quantify the potential errors in a production environment induced by the practice of sharing correction factors and apply those errors to different quality assurance systems. The work is based largely on correction factors generated by MaineDOT for the same design in multiple ovens across two laboratories. The difference in mixture type was evident in the correction factor data and the difference in correction factors in the same design ranged from 0.0% to 0.43%, with most differences between 0.07% and 0.15%. Larger differences in correction factors were observed between different laboratories then when they were generated for different furnaces in the same laboratory. Analysis of acceptance data and percent-within-limits simulations showed that sharing of correction factors, even in cases when the differences are small, resulted in significant impacts on quality acceptance and payment. The added variability can result in errors in assessment of quality, errors in payment to the producer, unnecessary corrective action by the producer, and a more variable finished product. Agencies and producers using AASHTO T 308 are encouraged to evaluate the differences in correction factors between their furnaces and laboratories to quantify the impact of errors on their quality assurance programs for asphalt mixtures.