| To this point, most research in asphalt concrete has focused on Mode I, or opening, cracking. However, a recent full-scale test section at the University of Illinois at Urbana-Champaign (UIUC) showed that cracks did not form in pure Mode I. If the cracks traveled vertically, the cracks could be considered a pure opening displacement, or Mode I, failure. However, the cracks did not form vertically, but instead traveled at an angle, indicating that there was also some sliding displacement, or Mode II, occurring. The combination of Mode I and Mode II can be referred to as Mixed-Mode.;This research began with a review of existing Mode I literature for asphalt concrete. In order to develop a strong understanding of the Mode I behavior of asphalt concrete, 28 asphalt concrete mixtures were tested using the Disk-Shaped Compact Tension Test, which captures fracture energy (Gf). These mixtures included 11 different types of asphalt cement, three testing temperatures, two different types of aggregate, two different levels of air voids, and two different contents of asphalt cement. In addition, two Mode I fracture tests were compared: the Disk-Shaped Compact Tension Test and the Single-Edge Notch Beam Test.;Three mixtures from the full-scale test sections discussed above were used to develop and validate a new Mode II test for asphalt concrete. No previous literature was found that attempted to capture Mode II fracture energy in asphalt concrete, so a test was developed from an extensive review of Mode II tests in the fields of metal, plastic, and PCC. Limited work has been performed in Mixed-Mode testing of asphalt concrete, but only Crack Mouth Opening Displacement (CMOD) was used. This research captured the Crack Tip Opening Displacement (CTOD) and Crack Tip Sliding Displacement (CTSD) in addition to CMOD. This allowed the comparison of three different values of fracture energy, or work, depending on the location and orientation of the data collection gages. Finally, the three asphalt concrete mixtures studied were simulated in Mode I to determine the total external work, with a break down of this work into the dissipated fracture energy, recoverable strain energy, and dissipated creep energy. |
