Evaluate the contribution of the mixture components on the longevity and performance of FC-5.
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2014-05-01
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Abstract: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.
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