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Mid-America Transportation Center

NDOR Effects of Aggregate Angularity on Mix Design Characteristics and Pavement Performance

Final Report
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Researchers

  • Principal Investigator: Yong Rak Kim (ykim3@unl.edu (402)472-1727)
  • Project Status
    Complete
    Sponsors & Partners
  • Nebraska Department of Roads
  • About this Project
    Brief Project Description & Background
    This research targets two primary purposes: to estimate current aggregate angularity test methods and to evaluate current aggregate angularity requirements in the Nebraska asphalt mixture/pavement specification. To meet the first research objective, various aggregate angularity tests are estimated with the same sets of aggregates and are compared by investigating their characteristics on testing repeatability, cost, testing time, workability, and sensitivity of test results. For the second objective, the effect of aggregate angularity on mixture performance is investigated by conducting laboratory performance tests (the uniaxial static creep test and the indirect tensile fracture energy test) of five mixes designed with different combinations of coarse and fine aggregate angularity and statistical analyses of five-year asphalt pavement analyzer test results of field mixtures. Outcomes from this research are expected to potentially improve current Nebraska asphalt specifications, particularly for aggregate angularity requirements and test methods to characterize local aggregate angularity.
    Research Objective
    The primary objective of this research is to develop guidelines that potentially help improve current Nebraska Superpave specifications particularly for aggregate angularity requirements and testing methods based on scientific investigation and experiments.
    Potential Benefits
    Successful research of this type will end up with tremendous cost savings because economically-optimized but better-performing pavements can be produced based on finding resulted from this study. Research outcomes from this study can also be incorporated with research findings from the previous Nebraska Department of Roads (NDOR) project (P556 "Restricted Zone Requirements for Superpave Mixes Made with Local Aggregate Sources") accomplished by the PI to deliver more comprehensive and meaningful guidelines for asphalt pavements in Nebraska.
    Abstract
    This research targets two primary purposes: to estimate current aggregate angularity test methods and to evaluate current aggregate angularity requirements in the Nebraska asphalt mixture/pavement specification. To meet the first research objective, various aggregate angularity tests are estimated with the same sets of aggregates and are compared by investigating their characteristics on testing repeatability, cost, testing time, workability, and sensitivity of test results. For the second objective, the effect of aggregate angularity on mixture performance is investigated by conducting laboratory performance tests (the uniaxial static creep test and the indirect tensile fracture energy test) of five mixes designed with different combinations of coarse and fine aggregate angularity and statistical analyses of five-year asphalt pavement analyzer test results of field mixtures. Results from the indirect tensile fracture energy test are then incorporated with finite element simulations of virtual specimens, which attempt to explore the detailed mechanisms of cracking related to the aggregate angularity. Results from the estimation of various angularity test methods imply that for the coarse aggregate angularity measurement, the AASHTO T326 method is an improvement over the current Superpave method, ASTM D5821, in that it is more objective and is very simple to perform with much less testing time. For the fine aggregate angularity measurement, the current Superpave testing method, AASHTO T304, is considered reasonable in a practical sense. Rutting performance test results indicate that higher angularity in the mixture improves rut resistance due to better aggregate interlocking. The overall effect of angularity on the mixtures’ resistance to fatigue damage is positive because aggregate blends with higher angularity require more binder to meet mix design criteria, which mitigates cracking due to increased viscoelastic energy dissipation from the binder, while angular particles produce a higher stress concentration that results in potential cracks.
    Project Amount
    $ 143,479