Standardizing Specimen Preparation for Indirect Tensile Cracking Test and Indirect Tensile at High Temperature Through Ruggedness and Fine-Tuning Studies

The Virginia Department of Transportation (VDOT) utilizes the indirect tensile cracking test (IDT-CT) and the indirect tensile at high temperature (IDT-HT) test as part of its balanced mix design (BMD) framework to evaluate asphalt mixture properties and support material acceptance decisions. While these index tests are critical tools for assessing asphalt mixture characteristics, considerable variability has been observed in test results, raising concerns about the effects of specimen preparation procedures on the repeatability and reliability of the outcomes. This study was undertaken to systematically evaluate the influence of key specimen preparation factors on IDT-CT and IDT-HT test results and to establish clear, data-driven guidelines to standardize preparation practices. The experimental program included a ruggedness phase and a fine-tuning phase, each designed to identify and quantify the effects of critical specimen preparation variables. Factors evaluated included mixture homogenization, sample splitting methods, sample and specimen heating duration, re-heating container type, specimen reheating, and heating processes. Laboratory testing was conducted on a range of asphalt mixtures using controlled procedures, and statistical analyses were performed to determine the significance of preparation factors on the test indices. The results highlighted that inconsistent preparation practices can introduce practical and sometimes statistically significant variability, potentially leading to improper material acceptance or rejection, particularly when comparing against specification thresholds such as the CT index. Based on the results of this study, refined specimen preparation practices were recommended to VDOT to help improve repeatability of laboratory BMD testing.