Theoretical Evaluation of Poisson's Ratio and Elastic Modulus Using Indirect Tensile Test with Emphasis on Bituminous Mixtures

The theoretical fundamentals used in evaluating Poisson's ratio and elastic modulus of materials using the indirect diametral tensile test are evaluated. With the current state of practice (ASTM D4123), the material properties are evaluated by the two-dimensional stress equations for a circular element supporting short-strip loading along the vertical diameter. Because of the inability of these equations to study misalignment of the specimen, the planar solution is analyzed. The analysis of the above two approaches indicates that the material properties predicted are relatively insensitive to specimen size and misalignment. However, the influence of aggregate inclusions in the vertical plane may cause significant propagation of errors in the vertical measurements outside the central half-radius that significantly affects the value of the predicted Poisson's ratio. The influence of aggregate inclusions in the horizontal plane does not appear to be a significant factor contributing in the horizontal displacement variations. Thus, determination of the elastic modulus from horizontal displacements alone has great potential in providing consistent, reasonable results with an assumed Poisson's ratio. In addition, a means of estimating the magnitude of the displacements and the required sensitivity of the measuring devices based upon expected Poisson's ratio and gauge length is presented. Finally, test control parameters based upon the ratio of vertical to horizontal deformations have been developed to check if the material being tested is within the elastic range as the test progresses.