Improved methods for extracting and recovering asphalts from pavement samples

Two new procedures for the purpose of extracting asphalt binder from hot-mix and pavement samples have been developed. Flaws in previous methods include: (1) the inability to completely remove solvent from recovered asphalt, (2) the inability to completely extract asphalt from the aggregate, and (3) a tendency to alter asphalt properties during extraction. The new methods improve precision and accuracy by minimizing these errors. The new procedures also conserve solvent and require less operator effort.;As specified, the standard ASTM solvent removal procedure is not capable of removing all of the extraction solvent from extracted asphalts. Analysis of residual solvent by Gel Permeation Chromatography (GPC) made it possible to determine optimal conditions for solvent recovery such as oil bath temperature, nitrogen flow, vacuum, and recovery time. Both the Abson and Roto-vap methods were studied. Neither provided consistent solvent removal for varying grades of asphalts. After raising recovery temperatures and extending recovery times, both methods were capable of removing all solvent from asphalts having 60;During extraction, asphalts are dissolved in strong solvents for several hours. ASTM D-2172B subjects asphalts to dilute solutions of trichloroethylene (TCE) at 80;Previous methods left up to 10% of the asphalt on the aggregate. This was due to poor mixing and the use of weak solvents. Several solvents were studied for their ability to extract strongly adsorbed material from aggregate fines. TCE with 15% ethanol (TCE/EtOH) and toluene with 15% ethanol (Tol/EtOH) showed good extractibility and were chosen as the extraction solvents for the new methods. The new methods also incorporated continuous mixing of the solvent-aggregate-asphalt slurry.;The SHRP (Strategic Highway Research Program) Method uses a tumbling extraction vessel with filters on one end. The pavement sample and solvent are mixed and then the extraction solvent is vacuum filtered into a rotary evaporator where the solvent is distilled. Several discrete washes with extraction solvent are required to completely extract the asphalt. Extracted viscosities of identical samples are precise to about 6% for one standard deviation.;The Auto Method uses the same extraction vessel as the SHRP Method, but it utilizes continuous mixing and solvent feed. Extract is continuously filtered from the extractor and distilled in the rotary evaporator. A custom recovery flask which is fitted with an asphalt sample cup allows for the recovery of asphalt in its eventual storage container. Precision for this method is not as good (11%) as in the SHRP Method.