Evaluation of Optimized Mixing Duration in Mixes Incorporating Coarse and Fine RAP Using a Performance Space Diagram

Abstract

To reduce the inherent variability in the production of mixtures containing reclaimed asphalt pavement (RAP) (referred to herein as RAP mixes), highway engineers prefer fractionated RAP material. The present study examines the performance of mixtures prepared using fractionated RAP at varying mixing times. Two sets of mixes were produced: one containing coarse RAP (19 mm–4.75 mm) and the other containing fine RAP (4.75 mm–0.3 mm). Both sets incorporated 40% RAP material and were produced at three mixing durations: 60 s, 120 s, and 180 s. To eliminate the variation in mix performance that arises due to difference in white rock gradation, an aggregate gradation within the gradation band of a surface course mix was determined through trial-and-error process. Mix performance was evaluated by conducting resilient modulus, flow number, and indirect tensile fatigue testing. During the mixing and compaction of hot recycled mixes, the aged binder in the RAP material softens and contributes to the mix’s workability, along with the virgin binder. Using this concept, the degree of RAP binder availability (DoAv) of the RAP mixes was determined to better understand the performance of the RAP mixes. At particular mixing times, the RAP binder availability estimated for fine RAP mixes was higher than the coarse RAP mixes. This led to higher resilient modulus and flow number values in fine RAP mixes compared to the coarse RAP mixes. In the fatigue test, with an increase in mixing time, both sets of RAP mixes exhibited an increase in fatigue life at lower strain levels (200 με). Considering the incorporation of fine RAP and coarse RAP material into thick bituminous layers (200 με), a performance space diagram was plotted to determine the optimal mixing time. Mixing times of >120 s for coarse RAP mixes and >60 s for fine RAP mixes are the optimized mixing times, as these mixes showed better rutting and fatigue performance than the target mix.