Fatigue characteristics of asphalt concrete mixtures

This report presents the state of the art in investigating fatigue cracking of asphalt mixtures, due to repeated load applications in the laboratory. A review of research relating to bitumen content and type, aggregate, filler, void content, mix stiffness, temperature, and moisture content is presented. The effect of test conditions such as controlied-stress or controlled-strain mode, rest period, and simple or compound loading upon the fatigue response of asphalt concrete is illustrated. Fatigue test apparatus such as two-, three-, and four- point bending test, wheel tracking machine, indirect tensile test, triaxial, direct tension, and push-pull test are reviewed. It is concluded from the comparisons between different apparatus that the test apparatus has a minor effect on fatigue results. Therefore it is reasonable to use the apparatus which is most economical and practical. An acceleration in fatigue testing (for example, testing at high loading speed with large stresses and/or without rest periods) could give unreliable fatigue results if the effect of such variables is not already known. Therefore the test conditions must be chosen with care. Neither the controlled-stress test nor the controlled-strain test can simulate the actual compound loading conditions that occur in the field. Nevertheless, the controlied-stress test is more reliable and practical than the controlled-strain test. More attention is desirable concerning the superposition effect of the variables influencing the fatigue resistance of the asphalt materials, which could induce a dramatic change in fatigue life