Influence of the interfacial composition on the adhesion between aggregates and bitumen: Investigations by EDX, XPS and peel tests

The study of the adhesion between aggregates and bitumen is necessary to enhance the lifetime of the roads. The purpose of this work concerns the interaction between the mineralogy of the aggregates and the adhesion force measured at the interface between bitumen and aggregate. The adhesion of bitumen was studied according to the mineralogy of the aggregates, which were made of dolomite rock or granite. A method was developed to measure the fracture energy during the peeling of the bitumen layer from the aggregate surface. The specific manufacturing of the samples ensured reproducible measurements using a constant thickness of the bitumen layer and by introducing a strengthened and flexible membrane into the bulk of bitumen. The peeling results demonstrated that the locus of the failure varied according to the mineralogy of the aggregate. The failure was cohesive during the peeling of the dolomite/bitumen system while the failure was partly interfacial concerning the granite/bitumen system. The interface between bitumen and minerals was characterized, before and after peeling. In case of the granite, the detection of sulfur by X-ray Photoelectron Spectroscopy (XPS) highlighted only the bitumen residues and allowed identifying the mineral compounds that weaken the interface between bitumen and granite. Finally, XPS analyses showed that the alkali feldspars of the granite induced a weak interface with bitumen.