Precision Estimates for Indirect Tensile at High Temperature and IDEAL Rutting Tests

Balanced mix design (BMD) integrates mechanical (i.e., performance-indicative) testing into asphalt mixture design to improve durability and longevity by balancing cracking and rutting resistance. Effective implementation of BMD requires simple, practical, and reliable mechanical tests suitable for routine production and quality assurance; however, standardized precision estimates necessary for specification development and acceptance criteria are not currently available for several emerging monotonic rutting tests. This study establishes ASTM-compliant precision estimates for two promising monotonic rutting tests: the indirect tensile at high temperature (IDT-HT) test and IDEAL rutting test (IDEAL RT). An interlaboratory study (ILS) was conducted involving multiple laboratories evaluating four dense-graded surface asphalt mixtures with varying rutting susceptibility. Precision estimates were developed according to ASTM standards, resulting in single-operator coefficients of variation (COVs) of 10.8% for the IDT-HT test and 8.5% for IDEAL RT, with corresponding multi-laboratory COVs of 12.8% and 17.0%, respectively. Additional proficiency testing for the IDT-HT test indicated strong operator proficiency, supporting the practicality of using these precision estimates in production settings. Moreover, the application of these precision estimates to production-level data demonstrated their appropriateness for field implementation, adequately capturing variability encountered during routine quality assurance testing. The developed precision estimates and statements facilitate the broader adoption of these tests within BMD frameworks, contributing significantly to the effective implementation of performance-based asphalt mixture specifications.