Perform An Investigation of the Effects of Increased Reclaimed Asphalt Pavement (RAP) Levels in Dense Graded Friction Courses

Abstract

In this study, a total of 28 mixture combinations were designed and evaluated to determine the maximum allowable amount of reclaimed asphalt pavement (RAP) material in friction courses without jeopardizing pavement cracking performance. The experimental factors included two RAP sources, four RAP contents, two virgin binders, and two mixture conditioning levels. RAP binder was recovered and blended with virgin binders at various RAP binder replacement ratios. All blended binders not only met the Florida Department of Transportation's (FDOT’s) specifications for virgin modified binders, but also had satisfactory binder fracture energy density (FED) values. Increased RAP content resulted in stronger (higher tensile strength) but more brittle (lower failure strain and lower FED) mixtures. However, even after long-term oven aging (LTOA) + cyclic pore pressure conditioning (CPPC), all RAP mixtures exhibited FED values above 0.75 kJ/m³ and energy ratio (ER) values well above 1.0, indicating adequate cracking performance. Higher RAP content generally resulted in higher ER values. Although the increasing trend was reversed between 30% and 40% RAP content, the ER at 40% RAP was still well above 1.0 and greater than the ER for 20% RAP mixtures. It should be noted that all RAP mixtures evaluated not only met Superpave design criteria, but also dominant aggregate size range and the interstitial component (DASR-IC) requirements. Satisfactory inclusion of up to 40% RAP was for well-designed mixtures with good gradation characteristics and with the use of modified asphalt binders.