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Laboratory and Field Evaluation of Modified Asphalt Binder in Alaska Pavements

Neat, unmodified PG 52-28 asphalt binder has been widely used in Alaska. However, experience indicates that hot-mix asphalt (HMA) produced with this neat binder may not be adequate in wearing courses for the various Alaskan climatic conditions. A highly-polymerized PG 64-40 HMA was recently placed in downtown Anchorage to address rutting and wear concerns in high-traffic areas and moderate low-temperature cracking concern. The low temperature grade of “-40” was selected instead of “-34” for improved workability. In addition, a “-40” low-temperature grade modified asphalt binder, PG 52-40, has been used recently in several paving projects in the Northern Region (e.g. 2015 Airport Way resurfacing project in Fairbanks). Furthermore, the Northern Region is interested in the potential use of a colder low-temperature grade binder, such as PG 52-46, to suit its specific climatic conditions. However, data is lacking in terms of materials characterization, performance prediction and field performance evaluation and monitoring of these modified asphalt mixes. It is essential to properly characterize the performance of the abovementioned modified asphalt binders as well as the resulting HMA in both the laboratory and the field. Phase I: Binder testing will be conducted on PG 52-28 (control neat binder), PG 64-40, PG 52-40 and PG 52-46 binders provided by selected suppliers. Testing will include bending beam rheometer (BBR), direct tension (DTT), asphalt binder cracking device (ABCD), Multiple Stress Creep Recovery (MSCR), Dynamic Shear Rheometer (DSR). Superpave classification testing to obtain continuous grade of each of the binders, plus data analysis related to rutting and low-temperature cracking resistance; Phase II: Pavement surveys and core sampling will be conducted on select field sites built with modified asphalt mixtures. Phase III: Hamburg wheel tracking (HWT) and/or Asphalt pavement analyzer (APA) at high hose pressure tests and the indirect tension (IDT) tests will be performed to evaluate rutting resistance and low-temperature cracking performance of asphalt mixtures, respectively. The IDT tests cover tensile strength and tensile creep compliance properties along with thermal cracking analyses.