Effects of Mineral Fillers on Properties of Stone Matrix Asphalt Mixtures

Stone matrix asphalt (SMA) is a gap-graded hot mixture that has higher proportion of coarse aggregate, lower proportion of middle-size aggregate, and higher proportion of mineral filler than a dense-graded mixture. Because of the high quantity of mineral filler, the type and quantity of this fraction should play a major role in the properties of these mixtures and their mastics. Determination of whether mastic and mixture properties can distinguish good mineral fillers from bad ones is the objective. Eight mineral fillers with known performance were obtained from three European countries. Mastics were tested for stiffness using a bending beam rheometer (AASHTO TP1), a dynamic shear rheometer (AASHTO TP5), and softening point of bitumen using the ring-and-ball apparatus (AASHTO T53-92). None of the tests distinguished among mastics with good and bad mineral fillers. Mixtures were tested for draindown of mastic using the National Center for Asphalt Technology draindown test, rutting using the French pavement rutting tester, low-temperature cracking using the indirect tensile test, workability using the U.S. Corps of Engineers gyratory testing machine, and moisture susceptibility using the ASTM D 4867 method. None of the tests distinguished among SMA mixtures with good and bad mineral fillers.