Development and Evaluation of Test Methods to Evaluate Water Damage and Effectiveness of Antistripping Agents

Moisture damage in hot-mix asphalt (HMA) mixtures occurs when water can infiltrate the pavement system. Pore water in mixtures can cause premature failure of HMA pavements, primarily through loss of adhesion between the asphalt binder and the aggregates or the loss of cohesion in the asphalt binder. Loss of adhesion can lead to stripping and raveling. The stripping of asphalt films from the surface of aggregate particles may occur as a result of poor adhesion of the asphalt to aggregate surfaces or displacement of the asphalt films by water which is attracted by hydrophilic aggregates, the latter being considered as true stripping. Siliceous aggregates are generally considered as the source of the problem since forms of crystalline quartz often inhibit the development of good adhesion, and in some cases cannot be coated with asphalt. Liquid antistrip agents are often added to asphalt cements to promote adhesion and prevent stripping. Lime treatment of aggregate prior to production of HMA is considered as an alternative measure in the prevention of stripping. Currently available laboratory testing procedures all evaluate the effects of water damage in the laboratory by measuring the relative change of a single parameter before and after conditioning (i.e., tensile strength ratio, resilient modulus ratio). These parameters do not distinguish between the different mechanisms present in a conditioned mixture, including the identification of the effects of pore water versus actual moisture damage. The current Superpave mixture design specification uses the AASHTO T-283 moisture susceptibility test for determining moisture sensitive mixtures. Most state agencies use AASHTO T-283 test, although there have been questions by the community at large about the accuracy of the test. Frequent false positives and/or negatives have been reported, leading to the initiation of this current study. This report developed test methods and criteria needed to relate mixture characteristics with the potential severity of moisture damage. The results showed that no single mixture property can be used to consistently monitor the effects of moisture damage in mixtures. Therefore, a fundamental theoretical framework for the evaluation of moisture damage in mixtures was developed, along with associated specification parameters. The new theoretical framework is based on the Florida HMA fracture model, developed at the University of Florida. A new moisture conditioning procedure using cyclic pore pressures was also developed based on fundamental considerations. The new conditioning and evaluation methods were tested on mixtures of varying aggregate types and gradations. The results presented show that the Florida HMA fracture mechanics model provides highly consistent evaluation of the level of moisture damage in mixtures. These test methods are also shown to be capable of evaluating the effectiveness of antistripping agents, considered to enhance the adhesion of asphalt binders to aggregate surfaces.

Language

  • English

Media Info

  • Media Type: Print
  • Edition: Final Report
  • Features: Figures; Photos; References; Tables;
  • Pagination: 337p

Subject/Index Terms

Filing Info

  • Accession Number: 01002830
  • Record Type: Publication
  • Report/Paper Numbers: UF #4910-4504-722-12, UF #00026632
  • Contract Numbers: BC 354, RPWO #11
  • Files: TRIS, USDOT, STATEDOT
  • Created Date: Aug 5 2005 1:55PM