Sensitivity of the Ideal Rutting Test to Variations in Conditioning and Testing Parameters for Assessing Asphalt Mixture Rutting Potential

ABSTRACT This study investigates how variations in testing procedures and conditions of the ideal rutting (IR) test, as performed in general accordance with ASTM 8360-22, Standard Test Method for Determination of Rutting Tolerance Index of Asphalt Mixture Using the Ideal Rutting Test, affect the assessment of rutting potential in dense-graded surface asphalt mixtures. Specifically, it explores the effects of specimen conditioning environments, loading rates, device types, and storage (lag and dwell times) on the IR test results. Four dense-graded surface asphalt mixtures, incorporating both unmodified and polymer-modified binders with varying rutting potentials, were evaluated. The results revealed significant differences in specimen conditioning times between water bath and environmental chamber methods. Notably, specimens conditioned in a water bath consistently exhibited lower rutting tolerance index (RTindex) values compared with those conditioned in an environmental chamber. However, the conditioning environment did not significantly impact the repeatability characteristics of the IR test. Furthermore, the study found that loading rate (within the range of 46–54 mm/min), loading frame (device type), and storage conditions (lag and dwell times) did not significantly affect either the repeatability characteristics or the outcomes of the IR test. Based on these findings, a preliminary performance criterion was established for the IR test, requiring a minimum RTindex value of 62 for dense-graded surface asphalt mixtures with “A” and “D” designations, conditioned in a water bath at 54.4°C for 1 h. However, this threshold is considered an initial benchmark and requires further validation for robust verification.