Comparison of Properties of RAP Aggregates Extracted by Ignition and Centrifuge Methods

Recycled Asphalt Pavement (RAP) is one of the most recycled materials in the United States. Due to rapid increase in the price of asphalt, engineers have tried to increase the percentage of RAP in new mixes. Different agencies suggest determining physical and consensus properties of RAP aggregate before selecting the percentage of RAP to be incorporated in the new mix. Ignition and centrifuge methods of extraction are two widely used methods to recover the aggregate from RAP. The recovered RAP aggregate is often tested for physical and consensus properties for evaluation. The properties of RAP aggregate also depend upon the method used for extraction of aggregate. In this study, an NCAT ignition tester was used for the ignition method of extraction and Trichloroethylene (TCE) was used as a solvent for the centrifuge method of extraction. The objective of this research was to evaluate and compare binder content, gradation, specific gravity, and absorption of the aggregates, fine aggregate angularity (FAA), coarse aggregate angularity (CAA), flat and elongated particles (F&E), and Los Angeles (LA) abrasion value. The test results did not show significant difference in coarse aggregate angularity, bulk specific gravity of fine aggregate, and gradation obtained by the centrifuge and ignition methods of extraction for the RAP. However, fine aggregate angularity and Los Angeles abrasion value were found higher in the ignition method of extraction than those in the centrifuge method. The bulk specific gravity of coarse aggregate was found to be higher using the centrifuge method of extraction than that using the ignition method of extraction.