Mechanistic-empirical pavement performance of asphalt mixtures with recycled asphalt shingles

Abstract

As highway agencies are in the process of adopting the new mechanistic-empirical pavement design guide, Pavement ME, it is unclear how asphalt mixtures incorporating Recycled Asphalt Shingle (RAS) will influence the design when mechanistic-empirical approaches are used. In this study, Pavement ME was used to evaluate the effects of RAS (with or without recycling agents [RAs]) on pavement performance. Furthermore, a cost analysis was conducted to assess the life-cycle cost of asphalt pavements constructed with RAS. Three different pavement structures were analyzed at three traffic levels (low, medium, and high) and for two climatic regions (cold and hot). Pavement ME predicted that the mix with 5% Post-Consumer Waste Shingle (PCWS) and 5% RA would be the best performer against roughness, rutting, and fatigue cracking. This is due to the stiffening effect of RAS, which is reflected in the dynamic modulus inputted in the software. While one would expect RAS to improve rutting performance, the superior fatigue performance of mixes with RAS was not expected given that the binder in RAS is an air-blown asphalt binder with poor elongation and relaxation characteristics. Results were compared to the Semi-Circular Bending (SCB) test results, which realistically predicted that the mixes with RAS and recycling agents would be the worst performers against cracking. This can be explained by the increased availability of aged RAS binder in these mixes when a recycling agent is used. Results of the cost analysis showed that the mixtures with RAS are more economical to produce. When considering the predicted performance of the mixes, the mix with 5% PCWS and 5% RA had the lowest cost over the pavement service life.