Effect of field compaction method on fatigue life of asphalt pavements

Field compaction of asphalt mixes has long been recognized as a major factor in the performance of the pavement. It has generally been concluded that the effect of compaction lies in the resulting density, air voids, and their variance, instead of in effects such as construction induced cracking or "checking". Indeed, the assumption has been that the effect of construction-induced cracks is more unsightly than physically detrimental to performance. This research demonstrated in numerous field trials that steel roller compaction is responsible for construction-induced cracks and that this is because of an incompatibility between the geometry of the roller and the mat and their relative rigidities. It has also demonstrated that a new type of flat plate compactor, the asphalt multi-integrated roller (AMIR), overcomes this problem and results in a smooth-textured mat, free of cracks. A series of fatigue tests were conducted on mixes from two Ottawa, Canada, field trials in which the major variables were steel roller versus AMIR compaction, direction of test loading, and type of mix. The results showed that AMIR compaction, for either type of mix, resulted in approximately double the fatigue life, all other factors being constant. Also, the direction of rolling in the field had negligible effect on the fatigue life of the AMIR compacted mixes but a very significant effect on the steel roller-compacted mixes in that the fatigue resistance to transverse cracking was much lower than the resistance to longitudinal cracking. The key conclusions are that construction-induced cracks as the result of the use of steel rollers can substantially reduce fatigue life, that direction of rolling in the field has a substantial effect, and that a new type of compactor, the AMIR, can overcome these problems.