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Fatigue failure can be attributed to cyclic (dynamic) loading energy which induces stresses and/or strains below the allowable strength and/or fracture strain level of a material. Since fatigue failures evolve over time, damage theories have been postulated to describe the mechanism by which this failure occurs. When a crack exists or forms early in the life of a pavement, fracture mechanics becomes the most relevant theory to explain the damage process. If conditions prevail to promote brittle fracture, the stress intensity factor and its critical value, Kc (or Gc) , becomes the most relevant parameter controlling the cracking and fatigue damage process. If conditions prevail to promote ductile fracture, the ductile fracture parameter, Jc, becomes the parameter for consideration. If conditions prevail to promote creep fracture, the C* - Line Integral offers the most relevant fracture criteria. Since the definition of Jc or C* in fracture mechanics imposes the condition that either parameter will degenerate into Kc (or Gc) when brittle fracture conditions, prevail, the utilization of Jc or C* provides the user with a powerful tool to characterize the fatigue/fracture process in a more general form. Since asphaltic mixtures can exhibit brittle and/or creep fracture, it is apparent that the C* - Line Integral can more closely capture the fatigue/fracture damage process than Kc or Jc. In this paper, a simple laboratory procedure to determine the C* - Integral, which is interpreted as the energy release rate, is presented. In addition, a mixture efficiency factor (`η*) is introduced. The mixture efficiency factor is used to examine and compare the efficiency of asphaltic concrete mixture in resisting fracture cracking using different aggregates and asphalt cement binders.
Cracking of asphalt mixtures, time dependentfracture mechanics, effects of aggregates and binders upon asphalt mixture cracking, testing for cracking potential of asphalt mixes
Director of R & D, CTL Engineering, Inc., Columbus, Ohio