EXAMPLES OF APPROACH AND FIELD EVALUATION: RESEARCH APPLICATIONS

This paper describes several projects that were developed as pavement experiments to investigate several aspects of performance. The projects described are representative in terms of both simple field observation of fatigue cracking and complete studies that include data on materials characterization, loading history and other aspects. The road experiments were selected to illustrate 2 factors: (a) the initiation and development of fatigue and fatigue-related cracks; and (b) the prediction of fatigue cracking as part of controlled experiments where knowledge of the pavements was sufficient to provide input for modeling their behavior. Conclusions formed on the basis of this project are presented. In general, the asphalt concrete surfaces on unbound aggregate bases tends to show initial distress through the development of short transverse cracks in the wheel path. However, cracks may be much more developed on the underside of the asphalt concrete. The formation of a typical alligator crack system is outlined. Tests indicate that depending on the tests indicate that depending on the assumed influence of repeated traffic loads on fatigue life (in terms of strain in the asphalt-bound layer) a predicted life to failure ranged from 9 to 12 years. It appears from the study that a reasonable estimate of design life in terms of fatigue cracking is feasible if the engineer is willing to take the time and care needed to do so. In another test project, careful characterization of the pavements and materials and also fatigue tests are provided. The traffic in terms of applied wheel loads was analyzed in conjunction with changes in subgrade moisture and temperature. Each increment of loading was accumulated as damage or distress. Predicted failure of the surface in fatigue was than compared with observed cracking in pavements. Predictions for pavement sections with crushed-stone bases were poor; those for treated bases were somewhat better, although not as good as might be expected.