Innovative Testing Protocol for Evaluation of Binder-Reclaimed Aggregate Bond Strength

Abstract

The durability of asphalt mixtures is strongly related to the adhesion properties developed at the interface between binder and aggregates. The loss of adhesion implies a rapid deterioration (e.g., stripping or raveling) of pavement layers under traffic loads, especially when the pavement is affected by the presence of moisture. Adhesion is a complex phenomenon related to the mineralogical and morphological nature of aggregates as well as to the chemical binder composition and the environmental conditions. The evaluation of adhesion has become even more complicated as an increasing percentage of reclaimed asphalt pavement (RAP) is used in the production of new asphalt mixes. Therefore, adhesion properties are also related to the mechanisms developed at the interface between virgin binder and aged binder that coats the RAP aggregate surface. An innovative procedure to evaluate the compatibility of the system virgin binder–RAP aggregate was proposed in this study. This procedure allowed the substrate of a RAP aggregate to be simulated in the laboratory and could integrate the binder bond strength test currently used to investigate bonding properties and water sensitivity of the system binder and virgin aggregates. Tests were performed with various aggregate sources, several modified binders, and two conditioning types (dry and wet). It was found that the procedure was able to discriminate different test configurations and variables. In particular, the artificial reclaimed aggregate substrate ensured higher adhesion performance compared with the virgin aggregate, especially in the wet condition, regardless of the modification level of the virgin bitumen.