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Development of a RTFO-Aging Test Protocol for WMA Binders and Its PG Grading

Warm mix asphalt (WMA) is one of the Every Day Counts (EDC) technology announced by the Federal Highway Administration (FHWA) and it is becoming increasingly popular in every state. Despite several benefits, the use of WMA is still not indisputable because of its possible rutting susceptibility. Although several laboratory rutting tests are currently in use in different states, very few of the tests use full scale loading conditions. Therefore, current test methods are good to evaluate the effects of different mix parameters, but often do not correlate well with field rutting distresses. The objective of this study is to evaluate a full-scale laboratory wheel load tester by correlating the rut depths with rut depth obtained from testing in Asphalt Pavement Analyzer (APA). A full-scale wheel load testing will eliminate the need of rigorous field evaluation. Laboratory made Hot Mix Asphalt (HMA) and Warm Mix Asphalt (WMA) have been used in dry and submerged condition for evaluation of this tester. After 1200 wheel passes the rut depth for WMA was always greater than the rut depth of HMA either in dry or submerged testing. This trend also corroborates with the APA test results. Binder was extracted and recovered from WMA and HMA specimens, and it was hypothesized that increased rutting and moisture susceptibility of WMA specimen is the result of reduced short-term aging of the WMA than that of HMA. Asphalt mix consist of different aggregate sizes. A study was conducted to investigate how total binder content in the mix is distributed among different aggregate size. The effect of aggregate size on aging of the mix, and consequently on its rutting performance was also studied. It was found that asphalt content associated with fine aggregate group is the highest among the three groups: coarse, medium and fine. In a mix, binder associated with fine aggregate is aged more than the binder associated with other aggregate and aging of a mix is mostly contributed by the aging of the fine portion of mix. To simulate the reduced aging of WMA binders in the laboratory, series of rolling thin film oven (RTFO) tests were conducted on two binder types at three different temperatures for four aging periods. Short term oven aging (STOA) was performed for same time duration on laboratory mix produced at the temperatures like those three RTFO aging temperatures. A RTFO aging model was developed correlating the rheological properties of STOA mix with RTFO aged binder to simulate the aging for WMA as well as for HMA. Investigation of rheological properties of RTFO and STOA binder depicts that change in aging index of binder follows a linear relationship with aging time and the rate of change of aging index also changes linearly with temperature. This study affirms that STOA exhibits more sensitivity to temperature than that of RTFO aging.

Language

  • English

Media Info

  • Media Type: Digital/other
  • Edition: Final Report
  • Features: Figures; Photos; References; Tables;
  • Pagination: 68p

Subject/Index Terms

Filing Info

  • Accession Number: 01686349
  • Record Type: Publication
  • Report/Paper Numbers: SPTC15.1-28-F
  • Files: UTC, NTL, TRIS, ATRI, USDOT
  • Created Date: Nov 26 2018 10:03AM