The Materials and Tests Division's Bituminous Section evaluated the ignition method as an alternative to the solvent method for determining asphalt content. Three ovens (the Gilson Asphalt Binder Ignition Furnace, Model HM 378; the NCAT Asphalt Content Tester; and the Troxler Asphalt Quality Analyzer) were evaluated for accuracy, precision, and performance. Ignition was proven to be an appropriate method of determining asphalt content. The test procedure resulting from this work is Tex-236-F, which is included in Appendix A.

The Superpave mix design system includes four consensus aggregate properties to ensure aggregate quality: coarse aggregate angularity, flat and elongated particles, fine aggregate angularity, and sand equivalent. In addition to determining these consensus aggregate properties, ascertaining aggregate gradations and specific gravities are also required to complete an optimal mix design. A method of extracting the asphalt from recycled asphalt pavement (or from quality control/quality assurance samples) that would produce a clean aggregate sample for analysis was needed. VDOT has used the ignition method for determining asphalt content and for the recovery of aggregates for gradation analysis since 1995. This study evaluated the effect on aggregate properties of samples extracted using the ignition furnace. For the purposes of the study, recycled asphalt pavement was artificially produced by mixing virgin aggregates with asphalt and aging the mixture prior to extraction in the ignition furnace. Consensus aggregate properties, specific gravity tests, and gradation analysis were performed on three replicates each of the virgin and recovered aggregates. Only the sand equivalent test and aggregate-specific gravities showed regular significant differences. It was found that the specific gravity values measured for aggregates recovered using the ignition furnace were closer to the measured values for the virgin aggregates than the effective specific gravity method which has been traditionally used for estimating a bulk gravity for recycled asphalt pavement. As a result of this study, recommendations were made to the Virginia Department of Transportation to change testing requirements on recycled asphalt pavement.

The ignition oven method has been gaining popularity because of its applicability to both laboratory and field conditions, its nondependency on chemicals, and its ability to evaluate both binder content and aggregate gradations. However, the use of this method requires the careful determination of correction factors for both binder content and aggregate gradations. The need for such correction factors stems from the fact that most aggregates experience a certain level of weight loss as they are subjected to elevated temperatures. These weight losses must be accounted for in order to accurately determine the binder content and aggregate gradation of HMA mixtures. It is well accepted that the most important step of the ignition oven test is the determination of an accurate correction factor. The implementation of the ignition oven method requires the highway agency to assess the performance of the local materials with the test procedure and to identify the mixture parameters that significantly impact the determined correction factor. In preparation for the implementation of the ignition oven test, the Nevada Department of Transportation (NDOT) conducted an extensive laboratory testing program to assess the impact of the various mix parameters on the determination of the correction factors. The experiment included aggregate source, binder type, lime, and testing temperature. This paper analyzes the data generated from the NDOT experiment and evaluates the impact of each of the considered factors on the correction factor. In summary, the analysis of the data generated in the NDOT experiment showed that the aggregate source and the addition of lime have the most significant impact on the determined correction factor followed by the temperature and binder type. However, if during a field project the binder or the method of lime application changes, this change would not require the determination of a new correction factor. The data also showed that the blank aggregate method would generate correction factors that are less variable than the known asphalt content method.

This paper describes the development and testing for the ignition method for determining asphalt content and aggregate gradation of asphalt-aggregate mixtures. The ignition method utilizes the mass of hot-mixed asphalt mixture before and after removal of asphalt cement by burning at 593 deg C (1100 deg F) to measure asphalt content. The recovered aggregate from ignition testing may also be used for gradation analysis. The test procedure is safer and simpler than current methods of asphalt content and gradation determination. The ignition method was evaluated in both the laboratory and field. In the laboratory, ignition testing was performed on 80 samples of hot-mixed asphalt. The ignition method proved to be precise and accurate in determining both asphalt content and aggregate gradation.