Ruggedness Study of Specimen Preparation and Fine-Tuning of Test Methods for IDT-CT and IDT-HT Test

About the report:

The Virginia Department of Transportation 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 framework to evaluate asphalt mixture performance and support performance-based acceptance decisions. Although these tests are critical tools for assessing performance 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 phase was designed to identify and quantify the effects of critical preparation variables. Factors evaluated included mixture homogenization, splitting methods, heating duration, 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 false positive or false negative performance assessments, particularly when comparing with specification thresholds such as the cracking tolerance index. Based on the study findings, a draft Virginia Test Method was developed to guide standardized preparation practices and improve the reliability, repeatability, and interpretability of IDT-CT and IDT-HT test results.

This study recommends that the Virginia Department of Transportation should (1) adopt the Virginia Test Method developed in this study as part of the standard specimen preparation procedures for Virginia Department of Transportation district laboratories and asphalt contractors to use within the balanced mix design process and (2) consider benchmarking the variability of IDT-CT and IDT-HT test results (i.e., cracking tolerance index and strength) following the adoption of the Virginia Test Method developed in this study to assess improvements in consistency and reliability.

_{Disclaimer Statement:The contents of this report reflect the views of the author(s), who is responsible for the facts and the accuracy of the data presented herein. The contents do not necessarily reflect the official views or policies of the Virginia Department of Transportation, the Commonwealth Transportation Board, or the Federal Highway Administration. This report does not constitute a standard, specification, or regulation. Any inclusion of manufacturer names, trade names, or trademarks is for identification purposes only and is not to be considered an endorsement.}

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