Identifying the mixing-induced homogeneity characteristics of asphalt mixtures containing reclaimed asphalt pavement (RAP) materials

Abstract The homogeneity of asphalt mixtures accounts for the pavement long-term durability, particularly for the recycled asphalt mixtures that includes reclaimed asphalt pavement (RAP) materials. Therefore, this study examined the mixing-induced homogeneity characteristics of recycled asphalt mixtures containing 40% RAP dosages. In specific, five mixing times and two ageing degrees of RAP binder were considered. The titanium dioxide powder was incorporated into RAP binders as an identification tracer. After the specimen preparation, the Computed Tomography (CT) technology was implemented to obtain the digital images of the specimen. In what follows, components of asphalt mixtures were separately identified. Accordingly, two homogeneity indexes were proposed to estimate the homogeneity of recycled asphalt mixtures. The results indicated that the distribution of the coarse aggregate contributed most to the specimen homogeneity, followed by the bitumen mastics and the air void. The extension of mixing time, to some extent, benefited the homogeneity degree of recycled asphalt mixtures. However, the newly formed clusters that occurred in the mixing process should be concerned and eliminated. For a cylinder specimen, the middle part of the specimen was more homogeneous than marginal positions.