Evaluate the Contribution of the Mixture Components on the Longevity and Performance of FC-5

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CAIT project no.: FDOT-RU3487

Fiscal Year: 2010/2011

Status: Final

Rutgers-CAIT Author(s): Thomas Bennert, Ph.D.

External Author(s): J. Darryll Dockstader

Sponsor(s): Florida Department of Transportation


Objectives of the research specified in RFRP #10/11-003, “Evaluate the Contribution of the Mixture Components on the Longevity and Performance of FC-5,” were as follows:

  • Examine and summarize what other state agencies are currently doing related to optimizing OGFC mixture performance;
  • Conduct laboratory testing using procedures suitable for OGFC mixture that would characterize the mixture’s ability to resist raveling and top-down cracking;
  • Determine how FDOT can optimize FC-5 mixtures to maximize their lifespan while working in the constraints of the aggregates and binder types available to Florida contractors.
  • Quantify the effects of deviations in FC-5 mixture components from mix design quantities and the expected performance life of FC-5 mixtures.

The focus of the project was to evaluate how to improve the longevity of FDOT’s FC-5 mixtures. In particular, what FC-5 mixture components have the greatest impact on improving the cracking and durability of the FC-5 mixture.

The data mining of FDOT Pavement Management System (PMS) database, provided valuable information regarding typical service life of FC-5 mixtures. Combined with material datasheets from production, the fatigue and durability of the FC-5 mixtures was found to be a function of the effective asphalt content of the mix, with little to no influence from traffic and pavement structure. This was further validated during an extensive field visit.

Laboratory testing consisted evaluating current mix design procedures, finer nominal aggregate size (NMAS) FC-5 mixtures, and the influence of production tolerances on the durability, cracking, and rutting performance.

The research conducted showed that asphalt contents could be increased by up to 0.6% if Pie-Plate testing was conducted using the PG76-22 and ARB-12 proposed for the mix. A 9.5 mm NMAS FC-5 mixture improves durability and fatigue performance over the current 12.5 mm NMAS FC-5, but rutting issues were observed in the Hamburg test, especially with the ARB-12 asphalt binder.

Current production tolerances for FC-5 mixtures seem appropriate, except for the 0.6% reduction in binder content and the finer side of the gradation tolerance for ARB-12 binders. The 0.6% below optimum asphalt content tolerance resulted in mixtures with poor Overlay Tester fatigue performance and higher Cantabro Abrasion Loss values. ARB-12 asphalt binders may create stability issues when FC-5 gradations are on the finer side of the production tolerance, as it is hyporthesized that the residual crumb rubber was pushing the aggregate skeleton apart. Stone-on-stone contact verification using the Voids in Coarse Aggregate (VCA) approach would help to rectify this potential issue.