Using Indirect Tensile Cracking Test Data for Quality Control and Acceptance

The Virginia Department of Transportation currently requires the use of the indirect tensile cracking test (IDT-CT) in accordance with ASTM D8225 in its balanced mix design specifications to evaluate the cracking resistance of several unmodified dense-graded asphalt surface mixtures. Although some studies have been performed, there is still limited information on testing processes that may have effects on the test results. This paper addresses the identification and assessment of factors that could have a significant effect on the cracking tolerance index (CT index) test results based on the IDT-CT when used for mixture quality control and acceptance by an agency, for example, specimen conditioning method, loading rate, and data collection frequency. Test results suggested that device type might be a significant factor for mixtures with relatively low CT index values. IDT-CT results were not dependent on the type of conditioning method (i.e., dry or wet). Further, they were not dependent on the loading rate applied, regardless of the machine type (servo-hydraulic or screw-drive) or the data collection frequency used over a range of 1 to 100 Hz. Sets of four and three test specimen replicates had single-operator and multi-laboratory precision estimates similar to those determined for five-replicate data sets.