Fatigue of Asphalt Paving Mixtures

Significant variables including load, environmental and mixture, influencing the laboratory fatigue testing of asphalt concrete are discussed. Analysis of laboratory fatigue data obtained using controlled-stress tests indicates that, in general, those factors tending to increase mixture stiffness tend also to increase fatigue life at a particular stress level providing the mixture is reasonably balanced and non-brittle. The reverse appears to be true for controlled-strain testing. Accordingly for heavy-duty pavements in which the asphalt-bound layers are approximately 6 or more inches in thickness and where the results of controlled-stress appear to apply, fatigue resistance can be improved by selecting a viscous asphalt (40-50 or 60-70 penetration) and by using a dense-graded, rough textured aggregate. At the same time, for light-duty pavements incorporating approximately 2 or less inches of asphalt-bound materials, for which controlled-strain conditions are applicable, a less viscous asphalt cement should be used (120-150 penetration) and the fines content should be reduced.