Evaluation of the failure planes in concrete containing reclaimed asphalt pavement (RAP) aggregates

Asphalt cohesion failure is mostly attributed to the lower performance of concrete systems containing reclaimed asphalt pavement (RAP) aggregates. However, there could be other modes of failure depending on several pa-rameters primarily the mineralogy of aggregates, rheology of asphalt binder, asphalt aging intensity, and characteristics of cement-mortar paste; identification of the dominating failure pattern may help in enhancing the potential of RAP for concrete composites. In the present study, the influence of these parameters on the failure mechanism of RAP concrete is studied by understanding the intermolecular interactions through surface-free energy concept and interfacial bond strengths adopting pull-off tensile strength approach; the studied ma-terials are limestone (basic), granite (acidic), and sandstone (slightly acidic to neutral) as parent aggregates, three asphalt binders having viscosities in the range of 800-4800 P with and without aging (short & two stages of long term aging), and four cement-mortar systems with varying characteristics strength between 10 and 40 MPa (M10-M40). The results revealed that the failure mechanism in RAP-concrete is a function of all the studied variations. The failure mode associated with RAP-concrete made with granite aggregates was found to be mostly an adhesive failure at the aggregate-asphalt interface. Cohesive failures were dominant in limestone and sand-stone aggregates when used for mortar grades <= M20, whereas, when the same combinations were used for higher mortar grades, they failed in adhesion mode at the mortar-asphalt interface. Also, the failure mechanism was observed to be dependent on the degree of oxidation of asphalt with aged asphalt mostly exhibiting cohesion failure.