Surface chemistry at the bitumen-aggregate interface

Surface chemistry of aggregates determines adhesion to bitumen and debonding or stripping due to water. In this paper, the authors report on the use of electrophoreses to investigate the proton transfer surface properties of both aggregate and bitumen in the presence of water. Electrophoretic test procedures were developed that take cognizance of the peculiar characteristics of these materials. Surface electrical parameters of aggregate particles as a function of pH reveal three characteristic surface chemistry regions under different environmental conditions. The isoelectric point is introduced as a quantitative parameter that describes surface acidity/basicity in aqueous systems. Furthermore, siliceous aggregate is prone to dissolution under surface alkaline conditions, while calcareous aggregate hydrolyze under similar conditions. Curves developed for bitumen and aggregate were superimposed and offer valuable qualitative information of bitumen-aggregate adhesion. A follow-up paper investigates the use of data generated during this research to assess water stripping quantitatively.