Innovative testing protocol for the evaluation of binder-reclaimed aggregate bond strength

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, 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. Nowadays, its evaluation becomes even more complicated as an increasing percentage of Reclaimed Asphalt 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 Reclaimed Asphalt aggregate surface. An innovative procedure to evaluate the compatibility of the system virgin binder/Reclaimed Asphalt aggregate is proposed in this study. This procedure allows to simulate in laboratory the substrate of a Reclaimed Asphalt aggregate and can integrate the Binder Bond Strength test currently used to investigate bonding properties and water sensitivity of the system binder-virgin aggregates. Tests were conducted using different aggregate sources, several modified binders and two conditioning types (dry, wet). It was found that this procedure is able to catch the differences between different test configurations and variables. In particular, the artificial reclaimed aggregate substrate ensured higher adhesion performance compared to the virgin aggregate, especially in wet condition, regardless the modification level of the virgin bitumen adopted.