Analysis of different reclaimed asphalt pavements to assess the potentiality of RILEM cohesion test

In the last years, RILEM Technical Committee 237-SIB proposed a new test protocol for reclaimed asphalt pavement (RAP) characterization, the cohesion test, with the goal to facilitate the identification of the most suitable solution for the recycling within new pavement layers. However, this procedure actually allows discriminating between different RAP sources but it does not exactly indicate the effective “activity” of the binder in the RAP.The present paper deals with the analysis of different RAP materials through the RILEM cohesion test. In particular, two “young” RAPs, different in composition and milled immediately after being laid, were aged in the laboratory and tested at different ageing levels. Moreover, an in-site aged RAP was tested as reference, either in neat conditions or after being sprayed with a rejuvenator. The results showed that the actual cohesion test approach, based on the evaluation of the indirect tensile strength (ITS), is not able to distinguish between RAP binders with stiff-brittle behaviour or good residual binding properties (despite the first is an unwanted condition while the second is a desired condition, both of them determine an increase in ITS). Differently, the Cracking Tolerance Index (CT Index) defined by ASTM D8225-19 can emphasize the RAP bitumen ductility and highlight any residual binding and adhesive properties. For this reason, a RILEM cohesion test improvement is proposed by including the CT Index calculation in the analysis.