Impact of Device Type and Specimen Preparation on the Variability of the Indirect Tensile Cracking Test (IDT-CT) at Intermediate Temperatures

Abstract

The Indirect Tensile Cracking Test (IDT-CT) is performed in accordance with ASTM D8225-19. This test method does not currently contain precision estimates. This creates potential issues when different test results are measured by individual laboratories conducting testing on the same asphalt mixture. In 2020, Phase I of an IDT-CT interlaboratory study (ILS) was conducted to establish precision estimates and statements for several indices associated with the IDT-CT (cracking tolerance index [CT index], fracture strain tolerance [FST], strength [S_t], and cracking resistance index [CRI]). This phase involved the evaluation of specimens fabricated and compacted by a third party laboratory and sent to participant laboratories for testing only. The objective of this paper was to assess the impact of device type and specimen preparation on the variability of IDT-CT results. This was accomplished through a second phase (Phase II) of the ILS program. This analysis involved the evaluation of specimens fabricated by the participant laboratories from loose mixtures, which were produced and sent from a third party laboratory along with detailed instructions for specimen fabrication and testing. The Phase II results suggest that device type might be a significant factor for mixtures with relatively low IDT-CT index values. Moreover, the precision estimates for the CT index, FST index, St, and CRI were determined. The precision estimates for single-operator conditions were similar, whether specimens of a given mixture were fabricated by the same laboratory or not. Finally, specimen preparation was found to induce additional variability in the precision estimates for multi-laboratory conditions.