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Mid-America Transportation Center

NDOR Moisture Sensitivity of Hot Mix Asphalt (HMA) Mixtures in Nebraska - Phase II

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
  • Brief Project Description & Background
    The ultimate goal of this research is to deliver guidelines that can help select appropriate material combinations resisting better to moisture damage based on clear understanding of moisture damage mechanisms and extensive testing results. Development and/or validation of appropriate testing protocols that can judge moisture damage sensitivity of asphalt mixes is another important objective of this study. Research outcomes from this study will be incorporated with research findings from the previous NDOR project (P564) to draw more comprehensive and general conclusions based on results from diverse mixes.
    Potential Benefits
    The project finds preliminarily that fly ask contributes to reducing moisture damage in hot-mix asphalt pavements. After further research, this could be found to be a cost-effective, successful supplemental material for more asphaltic pavements.
    Abstract
    Performance changes and fundamental material characteristics associated with moisture damage due to various anti-stripping additives in asphalt mixtures are studied through various experimental approaches and a numerical simulation. Three additives (i.e., one reference additive, hydrated lime, and two alternative additives: fly ash and cement) are investigated by adding them into two types of mixes (SP2 for low-traffic-volume roadways and SP5 for high-traffic-volume roadways) where two different asphalt binders (PG 64-22 for the SP2 mix and PG 70-28 for the SP5) are used. Two asphalt concrete mixture scale performance tests, the AASHTO T-283 and the APA under water, and two local-scale mixture constituent tests, the boiling water test (ASTM D 3625) and the pull-off test, are conducted to characterize the effects of binder-specific anti-stripping additives on the binder-aggregate bonding potential in mixtures. The pull-off tensile strength tests are then numerically modeled through the finite element technique incorporated with the cohesive zone modeling approach to seek more fundamental scientific insights into the effect of each anti-stripping additive on the overall moisture damage resistance. Results from laboratory tests and numerical simulations indicate that the SP5 mixtures, where high-quality aggregates and polymer-modified binder are used, are fairly self-resistant to moisture damage without treating any anti-stripping additive and do not show any visible sensitivity among additives, whereas the effects of additives and their sensitivity are significant in the SP2 mixes that use the unmodified binder PG 64-22 and low-quality aggregates. With the limited amount of test data, hydrated lime seems to perform slightly better than other additives, particularly with longer moisture-conditioning time. Fly ash contributes to reducing moisture damage by improving binder-aggregate interfacial properties, which are validated from the integrated experimental-computational evaluation.
    Project Amount
    $ 114,188