Andrew A. Cascione

Reconsideration of the fatigue tests for asphalt mixtures and binders containing high percentage RAP

Abstract When applying reclaimed asphalt technology in a flexible pavement project, most performance concerns are related to low temperature and fatigue cracking since the stiffness of the HMA mixture could dramatically increase through adding a high percentage of reclaimed asphalt pavement (RAP) material. The purpose of this study is to evaluate asphalt mixtures with high RAP contents, prepared using two RAP addition methods, for their performance based on fatigue-cracking resistance rather than relying on volumetric properties. Asphalt mixture samples were prepared with three RAP binder content replacement percentages (30, 40 and 50%) using two preparation methods: the as-is RAP gradation (traditional method) and the splitting of the RAP gradation into coarse and fine fractions (fractionated method). Asphalt mixture beam fatigue and binder fatigue time-sweep tests were performed. Beam fatigue samples also underwent freeze–thaw cycling for freeze–thaw damage evaluation. Rather than basing the performance based solely on S–Nf curves to illustrate the fatigue performance, the beam fatigue test data was analysed through a dissipated energy approach. Faster fatigue degradation was observed for the 40% RAP binder and beam mixture when subjected to repeated loading. From a morphology aspect, this can be explained by the binder’s phase separation and physical hardening effects.

Utilization of Post Consumer Recycled Asphalt Shingles and Fractionated Recycled Asphalt Pavement in Hot Mix Asphalt

The use of recycled materials for roadway construction has received increased interest from transportation agencies in the past several years. One commonly overlooked recycled material is the use of post consumer recycled asphalt shingles (RAS) in hot mix asphalt (HMA). With the availability of post consumer recycled asphalt shingles (RAS) increasing in the United States, there is a growing interest in the application of post consumer RAS in HMA. More than 10 million tons of post consumer shingles are being placed in landfills annually. These shingles contain and estimated 20 to 30 percent asphalt. The research presented in this paper studies the effects of post consumer shingles on the performance of HMA and its compatibility with fractionated recycled asphalt pavement (FRAP), the sizing and subsequent proportioning of RAP for use in HMA. In the summer of 2009 a field demonstration project was conducted by the Illinois State Toll Authority on Interstate Highway I-90. Eight mix designs containing five percent RAS and varying percentages of FRAP were developed and placed in three different areas of the pavement structure: the base course, the shoulder binder course, and the shoulder surface course. The field demonstration included five experimental sections and three control sections. Production and laboratory samples of the mixes were obtained for dynamic modulus testing. Master curves for each of the mixes were constructed and analyzed for material response at different temperatures and loading conditions. These material characteristic results indicate the experimental mixes contain an increased resistance to permanent deformation without a significant decrease in low temperature cracking susceptibility.