Effects of adhesion promoters on the contact angle of bitumen-aggregate interface

Herein, the evaluation of the effectiveness of several adhesion promoters for asphalt according to the chemical and mineralogical nature of the stone was investigated. From research in the road construction sector, the most common types of activators present on the market are classified according to the chemical nature of their active ingredient: amides, polyphosphoric acid (PPA) esters and organosilanes. Therefore, for each of these families, the adhesive properties of the corresponding modified bitumen loaded with a fixed amount of active agent, were tested on four types of stone materials. X-Ray Powder Diffractometry (XRPD), X-Ray Fluorescence (XRF) and Environmental Scanning Electron Microscope Energy Dispersive Spectroscopy (ESEM–EDS) were carried out in order to establish the chemical and mineralogical nature and identify the agglomerate structures of the selected inert rocks. Among various screened products, the organosilane-based additive showed excellent adhesive performances, independently of the chemical composition of inorganic interfaces, as confirmed by both contact angle and boil test measurements. Conversely, basic nature activators such as amides and those with an acidic nature, such as the esters of PPA, were greatly affected by the type of mineral substrate. Finally, the effect of added adhesive agents on the viscoelasticity of modified bitumen was checked in the linear regime by oscillatory rheology. Differences in the adhesive properties observed among the tested classes of amphiphilic binders were discussed in terms of difference in the sizes of their respective head groups.