Durability Issues of Asphalt Pavements (Polymer Modifiers)

OBJECTIVES: The objectives of this study are: 1) to evaluate the durability ofSuperpave asphalt pavements (with or without polymer-modifiers) through appropriate laboratory test and field investigation, 2) to investigate strategies for improving the durability of Superpave mixes, including the possible option of using polymer-modifiers with higher asphalt content and other options, 3) to recommend methods to address potential durability issues on Superpave mix, 4) to recommend the appropriate application procedures of using polymer-modifiers, if they are proven effective in enhancing asphalt pavement durability. BACKGROUND: The Superpave specification has been implemented in Kentucky since 1997. With the usage of Superpave mixes and polymer-modified asphalt binders, pavement rutting, once a widespread concern in Kentucky, has been partially solved. However, now there is a concern for the durability of these pavements. The coarser mixtures provide greater opportunity for the flow of moisture and air through the mat, which may result in stripping and premature oxidation. This research will investigate the durability issue of Superpave mixtures currently used in Kentucky through analyzing the performance data. In addition, the performance and the proper application of polymer-modified asphalt binders in Kentucky remains a question. One recommendation that appears to emerge from the first round of data from the National Center for Asphalt Technology (NCAT) Test Track is that mixtures containing polymer-modified binders can accommodate higher asphalt binder contents, and lower target air-void contents, than unmodified mixtures. If this could be proven true in Kentucky, it will be beneficial to Kentucky's asphalt pavements. If an extra 0.2 to 0.3 percent of asphalt could be accommodated in modified mixtures without fear of rutting or flushinglbleeding problem, the life of these mixtures could be lengthened. This research will compare the performance of asphalt binders with or without polymer-modified binders. If polymer-modified binders are found effective, the appropriate application procedure will be recommended. FY 2006 ACCOMPLISHMENTS: A review of literature was continued to determine available sources of information concerning the durability of Superpave mixtures, laboratory durability testing methods, and the performance of polymer modifiers. Field data was collected from pavement sections using Superpave mixtures and conventional mixtures, with polymer modifiers or without polymer modifiers. A large laboratory testing program was initiated, with some cores being tested by the Asphalt Institute. Test results were compared to design specifications, and recommendations were made based on these comparisons. FY 2007 PROPOSED WORK: Additional field samples will be collected. These new cores will be tested for percent AC, gradation, density, and other parameters. Based on the research results, revisions or supplements to the current asphalt pavement specification will be identified with the Research Advisory Committee. Possible recommendations will be investigated. All data will continue to be analyzed in order to make recommendations which will lead to a conclusion, and a report will be finalized. PROJECTED COST THROUGH FY 2006: PROGRAMMED COST FY 2007: TOTAL ESTIMATED COST: $176,000 $ 65,000 $240,000