Triaxial Testing of Bituminous Mixtures at High Confining Pressures : Final Report

Abstract

This laboratory study investigated the triaxial testing of bituminous mixtures at high confining pressures. The object of this research was to develop a better understanding of the basic factors that contribute to the development of shearing strength in bitumlnous-aggregate mixtures. Two aggregate gradations were used. They were referred to as open-graded and one-size, and were incorporated with an asphalt cement into bituminous mixtures. The open~graded and one-size mixtures were chosen because they both perform satisfactorily as paving mixtures for many service conditions, but only the open-graded mixture possesses adequate stability when evaluated by conventional testing methods. In addition to aggregate gradation, the other variables considered in this investigation were confining pressure, specimen height, type of aggregate, and asphalt content. The triaxial compression test was selected to measure the shearing resistance of these bituminous-aggregate mixtures at a range of confining pressures from 0 to 150 psi. The rational triaxial test provided a fundamental means for the determination of the various factors that contribute to the stability of bituminous mixtures. However, test specimens having a height to diameter ratio less than two also were fabricated in order to measure the influence of specimen height on the triaxial stability at high confining pressures. This phase of the research investigation was designated as the irrational triaxial test. For both the rational and the irrational triaxial tests, the open-graded mixture showed strength properties with a direct correlation to the Coulomb equation.