Comparison of data interpretation procedures for indirect tensile creep test for linear viscoelastic materials

The current standard in the US to interpret the IDT test results (AASHTO T 322-03) is based on the procedure proposed by Roque et al. 1992. The alternative procedure (Zhang-Drescher-Newcomb, ZDN) was proposed by Zhang et al. 1997 and it utilizes elastic-viscoelastic correspondence principle to determine volumetric and deviatoric parts of the creep compliance function. This paper compares both IDT interpretation procedures and proposes improvements to the ZDN method based on the correction factors found in AASHTO. The comparison is done in two ways: first, procedures are applied to the Finite Element Analysis (FEA) results and second all interpretation procedures are applied to the experimental results on two plastic reference materials. For verification, creep compliance for the reference materials is also determined from 3-point bending test. It was concluded that average creep compliance functions determined from the IDT and 3-point bending tests are virtually the same and improved ZDN procedure yields practically the same compliance values as AASHTO standard. Finally, the paper includes distributions of equation coefficients for the improved ZDN procedure that were determined from 178 IDT tests on asphalt mixtures. Example plots of volumetric and deviatoric parts of the creep compliance function are also shown. Improved ZDN procedure can be useful in examination of the bulk behavior of asphalt mixtures and viscoelastic materials in general.