A Laboratory Study on the Effect of High Rap and High Asphalt Binder Content on the Performance of Asphalt Concrete

Abstract

This thesis investigates the effect of added asphalt binder content on the performance and volumetric properties of asphalt concrete mixes containing Reclaimed Asphalt Pavement (RAP). Mixes with three different percentages of RAP (0%, 20%, 40%) obtained from an asphalt producer and three different percentages of asphalt binder (design asphalt content, design +0.5%, and design +1.0%) were evaluated. Additionally, a laboratory produced mix containing 100% RAP with four asphalt binder contents (0.0%, 0.5%, 1.0% and 1.5%) was also evaluated in order to determine the binder level that optimizes mix performance for the extreme case in RAP utilization. Performance of the mixtures was evaluated based on three criteria: stiffness (dynamic modulus), fatigue resistance (flexural beam), and rutting resistance (flow number). Results showed that a 0.5% increase in binder content improved both the fatigue and rutting resistance of the 0% and 20% RAP mixes with only slight decreases in dynamic modulus. However, the addition of various amounts of binder to the 40% RAP mix led to a significant decrease in rutting resistance with little or no improvement to fatigue resistance. Volumetric analysis was performed on all of the mixes to determine how the added binder content affected mix volumetric properties. Results of volumetric testing, specifically asphalt content and Voids in the Total Mix (VTM) at the design compaction effort, Ndesign, revealed that the 40% RAP mix incorporated a significantly higher level of binder during plant production which very likely contributed to the decrease in rutting resistance once additional binder was added in the laboratory. Additionally, the gyratory compaction effort that would result in 4 percent VTM at the optimal binder content over the three performance tests, N4%, was calculated for each mix. Results indicated that the VTM for the optimally performing 20% and 40% RAP mixes were well below current Virginia Department of transportation (VDOT) production standards. In addition, N4%, for the optimally performing 20% and 40% RAP mixes was 50% or less than the current design compaction effort of 65 gyrations.