Adhesion properties of warm-modified bituminous binders (WMBBs) determined using pull-off tests and atomic force microscopy

Abstract

The aggregate-binder bond is one of the main factors that affect the durability of asphalt mixtures. This can be investigated based on the energy required to fracture the adhesive bond between binder and aggregate. In this study, the effects of Sasobit, Rediset WMX and Rediset LQ on the adhesive bond strength of an aggregate-binder system is investigated using the pull-off test. Test data are compared with the nano-scale adhesion force determined using atomic force microscopy (AFM) using the PeakForce Quantitative Nanomechanical Mapping (PFQNM) method. The impact of warm mix additives, test temperature and binder grade on the practical work of fracture was investigated. It was found that Sasobit, Rediset WMX and Rediset LQ increased the practical work of fracture by 170%, 100% and 143%, respectively, for the aggregate-binder system produced using 40/60 Pen binder, and 70%, 25% and 50%, respectively, for the system produced using 100/150 Pen binder. The contribution of warm mix additives in improving the practical work of fracture has been linked to the adhesion force determined using AFM. AFM offers great advantage in characterising the nano-scale properties which were shown to include co localisation of nano-topography with adhesion, ease of sample preparation and reduction in experimental time relative to the direct tension pull-off test.