Characterization of Intermediate Temperature Fracture Properties of Asphalt Mixtures as Measured with Different Tests

Different test methods have been used to predict the performance of asphalt pavement by addressing the cracking mechanism. Based on the preference shown by highway agencies, the two most prevalent tests are the Indirect Tensile Asphalt Cracking Test (IDEAL-CT) and the Illinois Flexibility Index Test (I-FIT). Both tests conform to the fracture energy–based principle in defining the cracking potential of asphalt concrete at intermediate temperature, and therefore, for quality assurance, many agencies use these tests interchangeably following convenience without comprehending the relationship, if any, between them. Therefore, the study aims to find an equivalency between the tests by evaluating the fracture behavior and different measured parameters that are used to develop the cracking indexes and subsequent performance. In this regard, 11 different mixes have been evaluated to predict the cracking potential following their significant properties. Although both tests consistently identify possibly poor mixes, there is no appreciable proportionality between them. Moreover, the tests exhibit different fracture energy and strength and show individual slopes in failure mechanism trends. In contrast to fracture energy alone, the postpeak slope and the strength of the mixture seem to correlate better with the respective indexes. In general, the tests are not interchangeable; therefore, the selection of a mixture following the index value should be based on carefully observed field performance rather than just convenience. It is also recommended to incorporate the field performance of mixtures to find a better correlation when selecting the appropriate test performance criteria.