Development of a method to determine surface energy components of mineral fillers

Abstract

The surface energy components of the mineral fillers in asphalt mixtures are of significant importance to the fatigue and healing properties of the asphalt mastic. However, the Washburn equation did not apply to mineral fillers when using the column wicking method because mineral fillers can hardly form a non-zero contact angle with any probe liquid. This paper developed a new model for mineral fillers wicking a probe liquid; this model established a relationship among the mass of the wicked liquid, the wicking time and the spreading pressure of the probe liquid on the mineral fillers. Based on the developed model, an experimental protocol was designed to determine the spreading pressure of three probe liquids on five types of mineral fillers, respectively. The Gravimetric Sorption Analyzer was employed to perform the vapor adsorption tests to determine the spreading pressure of toluene on each type of mineral fillers; the Tensiometer System was utilized to measure the mass of probe liquids rising into the filler samples, respectively. Based on the test results, the spreading pressure of every probe liquid on each filler sample was determined, which was then used to solve for the surface energy components of the mineral fillers.The surface energy components of the fillers were compared with those of the coarse aggregates from the same quarry. Significant variations were identified in each component between the fillers and the corresponding coarse aggregates, which demonstrated the importance of the geometric characteristics of the aggregates to their surface energy components. Furthermore, an asphalt binder was selected to evaluate its adhesive bond energies with the fillers and the corresponding coarse aggregates, respectively. With the same asphalt binder, the nonpolar components of the fillers were smaller than those of the corresponding coarse aggregates, while the polar components and the total adhesive bond energies of the fillers were larger than those of the corresponding coarse aggregates. The differences among the components of the cohesive bond energy and the adhesive bond energies suggested that cracking and healing per unit length would need different energies in the three media, asphalt film, asphalt mastic and asphalt-aggregate interface. These differences would significantly influence the cracking development in asphalt mixtures because cracks would always grow along the easiest path that would need the lowest energy to create crack surfaces.