Volume 2, Issue 10 (November 2005)
Characterization of Asphalt Concrete by Multi-Stage True Triaxial Testing
The feasibility of an existing servo-controlled true triaxial (cubical) apparatus for evaluating the mechanical response of nominal 4-in. cubical specimens of asphalt concrete (AC) under multi-axial stress states has been investigated. The apparatus allows the testing of specimens along a wide range of stress paths and stress levels that are not achievable in a conventional uniaxial or cylindrical apparatus. A multi-stage testing scheme can be followed by simultaneous control of the major, intermediate, and minor principal stresses directly applied to the specimens. Two cubical AC specimens cut from two WestTrack block samples were subjected to a series of multi-stage stress paths that included triaxial compression (TC), triaxial extension (TE), simple shear (SS), conventional triaxial compression (CTC), conventional triaxial extension (CTE), and cyclic conventional triaxial extension (CCTE). Experimental data were analyzed to assess volumetric creeping properties, resilient response, plastic deformation response, Poisson's ratio, loss angle, and dilatancy of asphalt concrete under general stress states. Test results highlight the potential of the cubical cell for mechanical characterization of asphalt concrete in a broad range of applications involving true triaxial stress states. Analysis of test results indicates all of the following: (a) Modulus of AC shows significant anisotropy in different orientations; (b) Volumetric creeping of AC is considerably significant at relatively high pressures; (c) AC shows significant dilatancy; and (d) Cubical Device can distinguish mixes of different performance.