Decreases in pavement program funding levels have encouraged paving agencies to adopt higher levels of recycled materials into their asphalt mixes. In order to fully evaluate the effects of recycled asphalt pavement (RAP) in Hot Mix Asphalt (HMA) mixes, the level of blending between the RAP and virgin binders in the final asphalt mixture needs to be determined. Asphalt mixtures are designed with the assumption that full blending between RAP and virgin binders is attained. However, the actual percentage of binder blending is unknown. Since the binder of asphalt mixtures with RAP is a combination of both the virgin binder and the binder from the RAP material, increasing the total RAP percentage of the asphalt mixture will increase the amount of aged RAP binder in the final mix. As a result, the ductility of the final product will be reduced. However, in addition to the increased stiffness effect, lower blending percentages can also reduce the total binder content of the asphalt mixture and reduce cracking resistance. In this study, the level of blending between RAP and virgin binders at the asphalt mix level was quantified through semi-circular bend (SCB) testing. Solvent extraction and recovery was conducted on RAP to isolate the RAP binder. Isolated RAP binder was manually blended with virgin binder at blending levels of 0%, 50%, and 100% to be able to produce SCB samples with different levels of blending. To quantify the actual blending percentages for two RAP sources in Oregon, the SCB test results of these samples (0%, 50%, and 100% blending cases) were compared to laboratory-produced samples wherein RAP and virgin materials were mixed traditionally. It was concluded that an average blending of 56.5% is to be used for mixture design. Recommendations on the considerations of blending in asphalt mixture design were also provided.
Asphalt emulsion, commonly known as tack coat, is the bituminous material applied between pavement lifts to provide an adequate bond between the two surfaces. This material is an interlayer membrane, which serves as a glue between pavement layers, allowing successive layers to adhere together and behave as a monolithic structure. This allows tensile strains at the bottom of the asphalt layer to be minimized, and reduces the chances of premature fatigue cracking and early pavement failure. Several engineered emulsions have been proposed to create a stronger bond compared to the commonly used CSS-1H tack coats of Oregon. This study quantifies the performance benefits of newly engineered emulsions from three different tack coat companies by using rheological and bond strength testing. The use of a simple set of rheological test procedures is proposed to predict the shear strength of the tack coat bond. Suggested rheological tests have the potential to lead to more robust methods of QA/QC to characterize tack coats at the binder level to forecast expected performance in the field.