Investigation on binder homogeneity of RAP/RAS mixtures through staged extraction

Abstract

There has been a growing concern in paving industry about the degree of blending between virgin and recycled binders as more and more recycled asphalt pavement (RAP) and recycled asphalt shingle (RAS) have been used in recent years. So far, only a few studies have been conducted in an effort to address the blending issues, among which a method named staged extraction, or progressive extraction, was used to extract asphalt binder from aggregates layer by layer and yielded promising results. However, this method is still controversial. This study validated the feasibility of staged extraction by addressing the concerns over solvent effects on testing results, potential selective dissolution of binder fraction by the solvent, desirable solvent selection and binder homogeneity of raw RAP and RAS materials. It was found that among the solvents used in the study, trichloroethylene (TCE) was the most effective for staged extraction that dissolved the asphalt binder without preferential dissolution. Meanwhile, TCE was also found to have the highest dissolution rate. The RAP/RAS binder was observed to be homogeneous throughout the film thickness. Ultimately, with TCE as the solvent, a step-extraction method with varying wash times was developed to improve on the typical equal-time extraction, and was applied on 50% RAP and 10% RAS mixtures. The new step-extraction method was found to be more effective than the equal-time extraction. Partial blending was observed within the asphalt film coating RAP aggregates, while the RAS-virgin blending on RAS aggregates should be further evaluated.