Evaluation of wheel tracking and field rutting susceptibility of dense bituminous mixes

Rutting in bituminous layers is a major mode of distress, especially in pavements with thick bituminous layers. Different binder and mix rutting specifications are adopted by agencies worldwide to address the issue of rutting in bituminous mixes. The wheel tracking test is also widely used to evaluate the rutting potential of bituminous layers which depends on the aggregate gradation, binder type and also on the method of mix design adopted. The present study was conducted to examine the relationship between laboratory wheel track rutting and field rutting of different mixes prepared with different aggregate gradations, binder types and binder contents selected using different compaction efforts. Fifteen pavement sections with different surface mixes were constructed on a national highway. Loose bituminous mixes collected from the field were compacted to prepare specimens for wheel tracking tests. Two sets of specimens were prepared to have (a) 7% air voids and (b) an air void content similar to that observed in the field 1 day after construction. The rut depths measured using a wheel tracking machine correlated very well with field rut depths measured after 1 year when the laboratory specimens were prepared at the same initial air void content as achieved in the field. As expected, the rut depth measured in the laboratory wheel tracker for specimens prepared with 7% air voids did not correlate well with 1 year rut depths of field mixes which had different initial air void contents. Limiting wheel tracking test rut depths have been identified on the basis of comparison of the field rutting performance of different mixes and the corresponding laboratory rutting performance of the mixes. Limiting criteria have been proposed for two limiting rut depths of 10 and 20 mm and for different traffic levels.