Fracture energy density of interstitial component of asphalt mixtures

Interstitial component (IC), referring to the finer portion of asphalt mixture, is primarily responsible for tensile properties and thereby strongly affects mixture cracking performance. Whereas mixture tests are usually complex and labor-intensive, determination of fracture properties with a simpler test on the IC portion will add values in terms of ranking mixtures and predicting mixture fracture properties. An interstitial component direct tension (ICDT) test, which was derived from the dog bone direct tension test originally developed for asphalt mixtures, was applied to determine the fracture energy density (FED) of mixture IC portion. FED describes the damage tolerance before fracture occurs and it is also a component associated with crack propagation. Two methods of strain determination were evaluated including a digital image correlation (DIC) system and a predictive equation derived from finite element analysis with load-head displacement as input. ICDT tests were conducted on the IC portion of two sets of four mixtures, which had identical coarse aggregate structure. The DIC system yielded greater failure strain than those based on load-head displacement. However, the ratios between the two values for all mixtures were almost constant, supporting the use of the predictive equation as a surrogate. Moreover, IC FED ranked these mixtures in the same order as mixture FED and more importantly, an excellent correlation was observed between IC FED and mixture FED of these mixtures. In conclusion, the ICDT test can be used to determine the IC FED, which provides valuable insights regarding the effect of IC characteristics on mixture FED.