Rutting and Cracking Performance of Asphalt Mixtures for 150 mm and 100 mm Diameter Samples Using Simple Performance Tests

The balanced mix design (BMD) approach has emphasized the implementation of simple performance tests such as the indirect tensile asphalt cracking test (IDEAL-CT) and ideal rutting test (IDEAL-RT) for evaluating cracking and rutting performance of asphalt mixes for quality control (QC) and quality assurance (QA). The threshold values for CTIndex and RTIndex developed by many departments of transportation based on IDEAL-CT and IDEAL-RT tests, respectively, have proven to be useful for highway agencies. However, these limits are applicable only when tested using 150-mm-diameter samples. In many countries, Marshall mix design using 100-mm samples is quite prevalent and also similar diameter field core and lab compacted samples are used for various testing purposes. Therefore, the CTIndex and RTIndex threshold criteria developed based on 150-mm-diameter samples are not directly applicable to 100-mm-diameter samples. Therefore, the present study aimed to develop threshold values of CTIndex and RTIndex for 100-mm-diameter samples for practical application. Nine plant-produced dense-grade asphalt mixtures with different aggregate sizes and binder types were collected from various highway projects. The IDEAL-CT test at 25 degrees C and IDEAL-RT test at 50 degrees C were conducted on 150-mm and 100-mm-diameter samples. The proposed threshold limits for 100-mm-diameter samples were 50 and 110 for CTIndex and RTIndex, respectively, which were significantly different than used for 150-mm-diameter samples. Furthermore, the performance space diagram (PSD) developed based on limiting threshold value of CTIndex and RTIndex further highlighted the importance of the selection of appropriate acceptance criteria.