An Investigation of Various Percentages of Reclaimed Asphalt Pavement on the Performance of Asphalt Pavements

With the increasing cost of asphalt binder and the growing concern over the availability of quality aggregates, the use of higher percentages of reclaimed asphalt pavements (RAP) has become of much interest across the country. Research has shown that the RAP recovered from construction sites still contains usable materials, both in the recycled aggregates and recycled binder. However, since the RAP binder has been aged during its service life, the use of RAP in new pavement construction may cause the stiffness of the blended binder to increase. Due to this increased stiffness, it is sometimes necessary for a "grade shift" in the virgin binder in order to result in the specifications for the desired performance grade. The use of higher percentages of RAP in construction would provide initial cost savings. However, a life cycle cost analysis was needed in order to determine whether use of higher percentages of RAP provided an economical advantage for the life cycle, not just initially. In order to predict life cycle costs, the fatigue life and rut resistance of mixtures containing various amounts (15%, 30% and 40%) of RAP were compared to a 100% virgin material mixture. The fatigue life and rut resistance of the mixtures were calculated from laboratory testing using Frequency Sweep Testing using Superpave Simple Shear Tester (SST) and Repeated Simple Shear Tests using SST. The SHRP A-003A surrogate models and the Asphalt Institute models were both used in order to predict pavement performance using the results from the Frequency Sweep Testing and the Repeated Simple Shear Test. Based on these results, the life cycle economic analysis was completed and the optimum percentage of RAP was determined for use in the construction of new pavements for NCDOT. The development of warm mix asphalt (WMA) technology over the recent past has sparked interest in many researchers, engineers and government officials. The use of WMA has incentives including fuel savings, lower emissions, longer hauling distances and longer construction seasons since the use of WMA allows for lower production temperatures. Research has also shown that the reduced production temperatures may reduce the amount of oxidative hardening which may help reduce thermal cracking and block cracking. Due to this benefit, along with the anticipated benefit of better compactability using WMA, it is thought that WMA can be used in mixes containing higher percentages of RAP since less oxidative hardening of the asphalt binder may occur for the already more stiff RAP binder. Mixtures with higher percentages of RAP often have issues with thermal cracking and block cracking due to the stiff binder from the RAP blending with the virgin binder. In order to determine how the use of WMA additives effect the binder rheology of blends containing higher percentages of RAP, Dynamic Shear Rheometer (DSR) and Bending Beam Rheometer (BBR) testing were performed on virgin, blended and RAP binders containing SasobitRTM, a WMA additive. These results can be used to determine the allowable amount of RAP that can be used with WMA.