About the research
As the cost of construction materials continue to rise and place financial constraints on transportation agencies, engineers are looking for sustainable methods that minimize construction costs and optimize the selection of materials used in asphalt pavements. Two methods that are beginning to receive considerable attention for highway construction are adding post-consumer recycled asphalt shingles (RAS) to hot mix asphalt (HMA) and increasing the percentage of reclaimed asphalt pavement being added to HMA through the process of fractionation.
The objective of this research is to characterize the effects of post-consumer RAS on the laboratory performance of HMA and its compatibility with fractionated recycled asphalt pavement (FRAP).
In the summer of 2009, a field demonstration project was conducted by the Illinois Tollway on the Jane Addams Memorial Tollway (I-90). Eight mix designs containing zero or five percent RAS and varying percentages of FRAP were developed and placed in the pavement shoulder. Production and laboratory prepared samples of the mixes were obtained for dynamic modulus, flow number, moisture sensitivity, beam fatigue, and fracture energy tests in addition to binder extraction and subsequent characterization. From the dynamic modulus testing, master curves were constructed to characterize the stress/strain response of the HMA samples. From the extracted binders, a suite of Superpave tests was conducted at different temperatures and frequencies to build master curves for analyzing how the addition of RAS binder affected the rheological properties of the mix binder blend. A statistical analysis was performed on the dynamic modulus and flow number test results to determine how the behavior of the asphalt materials containing RAS differed from the behavior of the asphalt materials not containing RAS when varying percentages of FRAP were a part of the mix designs.
Laboratory test results indicate that the mixes containing five percent RAS with less than 40 percent recycled materials exhibit an increased resistance to permanent deformation while maintaining satisfactory performance to fatigue stresses, low temperature cracking, and freeze-thaw durability. Although the low temperature binder performance grade increased with the addition of recycled materials, the mix performance test results did not follow that trend, indicating fibers in the RAS materials likely contributed to the performance of the mixtures.