Asphalt-Aggregate Interactions Characterized by Zeta Potential and Retained Strength Measurements for Natural and Organosilane-Treated Aggregates

Abstract

Zeta potentials in water have been measured for a poorly performing, easily stripped hard limestone, a well-performing hard limestone, a sandstone, a rhyolite, soda lime glass beads, and for eight AC-20 asphalt binders. Four of the binders selected to represent a range of zeta potentials were combined with the sandstone, the limestones, and the glass beads according to Oklahoma Department of Transportation mix formulas and tested for retained strength. The good hard limestone was the best overall performer with retained strengths of 96 to 100 percent, the poor hard limestone was acceptable, overall the sandstone was unsatisfactory; and the glass beads did not survive the retained strength preconditioning procedure. The aggregates were then treated with organosilane derivatives to chemically modify their surfaces and to change the aggregate zeta potential. For example, the zeta potential of the poor hard limestone was made to be closer to that of the good hard limestone. The modified aggregates were then used in the same mix and the retained strengths measured. The good hard limestone mix exhibited no change in retained strength; however, the poor hard limestone, the sandstone, and the glass bead mixes gave excellent retained strengths.