Abstract

A laboratory investigation was performed to determine if the amount of Crumb Rubber Modifier (CRM) in Recovered Asphalt Pavement (RAP) had any adverse effects on the recycling and recycled mix properties. The Florida Department of Transportation (FDOT) currently uses 12 percent CRM prepared by the wet process in open graded friction course (FC-2) which are typically used on interstate and primary highways.
Pavement recycling has been an operational system in Florida since 1983. Therefore, there has always been a concern about any change in paving mixture formulation that could affect recycling operations. Modified asphalt blends were prepared with an AC-30, 12 and 18 percent of 20, 40, and 80 mesh CRM. Simulated RAP mixtures were prepared at a design binder content of 6.5 percent with these blended binders. All mixtures were compacted in the Gyratory Testing Machine (GTM) to simulate field compacted and traffic densities.
Analysis of Variance (ANOVA) and Duncan groupings were performed to evaluate the effect of the variables. The percent of CRM had no effect on gyratory shear strength for the as-compacted or initial traffic densified mixtures. However, a difference occurred at final densification. Rubber type (mesh size) had no effect on shear strength. Age hardened RAP containing 6 percent of 40 and 60 mesh CRM had no discernable effect on shear strength. It was concluded that the mixtures evaluated in this investigation were relatively insensitive to variations in formulation and compacted density.

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