Laboratory and Field Evaluation of HMA with High Contents of Recycled Asphalt Pavement

To determine if a higher percentage of recycled asphalt pavement (RAP) materials can be used in Iowa's state highways, three hot mix asphalt (HMA) test sections with RAP amounts of 30.0, 35.5, and 39.2% were constructed. RAP materials were fractionated to meet Superpave mix design requirements. The field densities of all test sections were measured at 94.0% and higher. After 20,000 passes were applied using a Hamburg wheel tracking device, rut depths were less than 3mm for all field mixtures. The binder was extracted from the field mixtures to identify the effect of RAP materials on the virgin binder. The extracted asphalt from test sections with 30.0, 35.5, and 39.2% fractionated RAP (FRAP) materials were stiffened from performance grade (PG) 64-28 (virgin binder) to PG 76-22, PG 76-16, and PG 82-16, respectively. To evaluate the low-temperature cracking behavior, a semicircular bending (SCB) test was performed on laboratory-compacted field mixtures. As the amount of FRAP materials increased, the fracture energy decreased, indicating a potential susceptibility to thermal cracking. Finally, condition surveys were performed on the test sections after 8 and 27months since construction. Although the test section with 39.2% FRAP performed the best in the first survey followed by 35.5 and 30.0%, it deteriorated at a higher rate, resulting in a similar performance level as the other two test sections in the second survey.