Investigation of Factors Related to Surface-Initiated Cracks in Flexible Pavements

Project summary:

Surface-initiated (top-down) cracking, and transverse cracking due to thermal effects in flexible pavements, are of major concern in Minnesota. Prior to this research, top-down cracking had been found to contradict the current pavement design models, which assumed uniform pressure at the contact of the tire and pavement, and predict that bottom-up cracks should develop instead. However, analyses indicated that significant tangential contact forces may develop on the pavement surface and that they would be likely to contribute to the top-down cracking observed on many roads. Transverse cracking, on the other hand, may act as a trigger, for stress concentrations in the vicinity of the preexisting cracks may occur when the pavement is subject to loading. This effect could not be investigated by means of the existing pavement models.

This project attempted to identify potential mechanisms for the occurrence of top-down cracking in pavements, as well as to investigate stress patterns and concentrations due to surface load and preexisting transverse (thermal) cracks. The study provided information on surface stresses derived from both theory and experiments. In particular, contact mechanics solutions were analyzed to gain information on loads that are subsequently used in performing numerical evaluation of surface stresses. The analysis employed three-dimensional computations using the finite element code ABAQUS, including comparisons of stresses for uncracked and cracked pavements. The final project report concluded that the presence of a transverse crack in the AC layer significantly increases the vertical stresses in the base, and also has a noticeable effect on the horizontal stresses in the AC layer.