The binder content of an HMA mix is one of the critical factors affecting the quality of the mix. The ignition oven is one widely used method for determining the binder content, however, its use is problematic with some types of aggregates, including dolomites. With these aggregates, the mass loss continues after the binder is burned off as the aggregates decompose and the test does not terminate at a stable mass. This study investigated the factors that affect this mass loss in problematic aggregates and developed a modified ignition oven procedure to limit this mass loss. The mass loss in the ignition oven was found to be both time and temperature dependent.

The mass loss is also related to the binder content in the mixture. When the binder in the mixture ignites, the oven temperature increases and exceeds the pre-set test temperature. Temperature variations inside the ignition oven result in higher temperatures in the vicinity of the upper basket; these temperature differences are even more pronounced when the binder ignites. These higher temperatures can result in increased mass loss with problematic aggregates. A test temperature as low as 427°C was found to be effective for removing the binder from a mixture.

Therefore a modified ignition oven procedure was developed to control the temperatures and limit the additional mass loss for problematic aggregates. The method involves placing half the total sample mass in the bottom basket only and running the ignition oven at a temperature of 427°C. This method was verified by testing six different plant produced mixes containing problematic aggregate and by comparing the results to results of the standard ignition oven method and to solvent extraction. The modified method is recommended for use with problematic aggregates or where the standard test method yields calibration factors greater than 1.0 or the test does not terminate automatically. .

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Hot Mix Asphalt, ignition oven, binder content, dolomite, SPR-2862

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Performing Organization

Joint Transportation Research Program

Publisher Place

West Lafayette, Indiana

Date of this Version