Using automated asphaltene determinator coupled with saturates, aromatics, and resins separation (SAR-AD™) to classify asphalt recycling agents as softeners, dispersants or destabilizers

The use of recycled asphalt (reclaimed asphalt pavement RAP) has been increasing in the United States, benefiting not only in terms of cost savings but also the environment. Industry and government have significantly promoted the development of methods for constructing pavements with high and ultra-high RAP contents. To achieve this goal, it is necessary to incorporate recycling agents (RA). Given the growing demand and market growth forecasts, different types of RA are being introduced, encompassing diverse sources and chemical compositions. Not all RA are created equal, so blind and effective approaches are required to evaluate and compare them, especially regarding action mechanisms and long-term aging. In this paper, the advanced SAR-AD method, combining the traditional SARA (saturates-aromatics-resins-asphaltenes) analysis with the Asphaltenes Determinator (AD), was used in parallel to rheological testing and other methods like Differential Scanning Calorimetry, to study 6 RAs from different sources. They were studied before and after aging, as received and blended with an aged asphalt binder at a constant rate of 7.5%. The action mechanism of each RA (ie softener, dispersant or destabilizer) was defined based on the impact on asphaltenes content upon blending with the aged asphalt: softeners have no effect, when dispersants decrease the expected asphaltenes content and destabilizers increase it. The thermal stability, describing the propensity to evolve chemically upon long-term exposure, was also assessed based on the evolution of asphaltenes content upon aging. It makes it possible to propose a classification of RAs based on their action mechanisms and thermal stability. This classification is shown to be very relevant to anticipate the high temperature properties of treated binders and how they evolve with aging. It is also shown that the classification is less relevant for the low temperature properties, which are rather controlled by the glass transition temperature of the RA.