Asphalt Content by Ignition Round Robin Study

Abstract

The National Center for Asphalt Technology (NCAT) has developed a test method to determine the asphalt content of hot mix asphalt (HMA) mixtures by ignition. In the ignition method, a HMA sample is subjected to 538 degrees C (1000 degrees F) in a furnace to ignite and burn the asphalt cement from the aggregate. The difference in weight of the sample before and after ignition is used to determine the asphalt content of the mixture. The aggregate recovered after ignition testing may then be used for gradation analysis. A round robin study was completed by NCAT to determine the accuracy and precision of the ignition method. This paper discusses the round robin test program and the accuracy and precision values determined for the measured asphalt content and gradation by the ignition method. Equipment for the procedure was provided along with laboratory prepared HMA samples to 12 participating laboratories throughout the U.S. Four replicates of four HMA mixtures containing different aggregate types, gradations and asphalt contents were provided for testing. The results of the round robin study show that the ignition method can accurately measure the asphalt cement content of HMA mixtures with greater precision than solvent extraction methods without significantly affecting the gradation of the aggregate.