University of California Pavement Research Center

The California Department of Transportation (Caltrans) recently increased to 25 percent the allowable percentage of reclaimed asphalt pavement (RAP) that can be used in new asphalt mixes. A Caltrans-industry task group, formed to consider recent legislation (AB 812) covering the use of RAP in new mixes, has proposed allowing an increase of up to 40 percent binder replacement from a combination of RAP and reclaimed asphalt shingles (RAS). Although these changes can reduce the amount of virgin binder required in new mixes, concerns have been raised regarding the influence that the aged binder in RAP and RAS will have on the new binder properties. Traditionally, solvent extraction and recovery have been used to characterize the rheological and performance properties of the asphalt binder in a mix. This approach has long been criticized for being labor intensive, for altering binder chemical and rheological properties, as being inappropriate for modified asphalt binders, and for creating hazardous chemical disposal issues. In the first phase of a UCPRC study described in this technical memorandum, alternative methods to solvent extraction and recovery were investigated for evaluating the performance properties of asphalt binders blended with RAP and RAS binders. These methods include testing asphalt mortars and fine aggregate matrix (FAM) mixes. This technical memorandum summarizes a literature review on the topic and includes key observations from preliminary laboratory testing. Results from this testing indicate that testing asphalt mortar is probably limited to binder replacement rates not exceeding 25 percent. Preliminary results from FAM mix testing indicate that this method is repeatable and reproducible, and that representative results can be obtained from dynamic shear rheometer (DSR) tests on FAM mix specimens. Proposed further research includes the following: Investigate effective binder replacement rates, the compatibility of virgin binder and aged RAP and RAS binders, the effectiveness of rejuvenating agents, and the influences of production time and temperature on the degree of diffusion and blending of virgin and aged binders. Investigate relationships between the results of asphalt binder and FAM mix testing and identify possible reasons for differences between results focusing on the effect of solvent extraction on blended binder properties. Develop a method for preparing simulated RAP binders that are representative of typical RAP binders at high, intermediate, and low temperatures. Investigate the suitability of two-layer asphalt binder testing as a method for understanding the diffusion/blending mechanism between virgin and RAP and RAS binders.