Effect of mixture characteristics on cooling rate of asphalt pavements

This paper is aimed at estimating the time available for compaction of a hot-mix asphalt mixture during night construction. Laboratory tests were conducted on dense-graded and porous asphalt (PA) mixtures to evaluate their mechanical properties. Temperatures and mix characteristics tested in the laboratory were determined to be those typically found in an asphalt lift from initial laydown through final compaction. In field, thermocouples were installed at different depths to measure temperature changes to decide pavement cooling times of the same mixes as used in the laboratory. The cooling behavior of asphalt concrete could be classified into the following three stages: rapid, transition and stable zone. The air void in the PA mix was found to contribute to heat loss and result in a rapid cooling rate when compared to that in a dense-graded mix. The cooling rate at depth of 0, 2.5, and 5cm showed an essential difference in the cooling rate initially. As the cooling process continued, the cooling rate became stable and reached a thermal equilibrium condition. An increase in lift thickness was shown to increase the compaction time. However, an increase in layer thickness more than 10cm might not increase the time available for compaction significantly. A regression model was developed to predict the time required to cool to the minimum temperature allowed for compaction at night. The predicted values were in good agreement with those measured in the field. This study shows that a simplified method to predict available compaction time can be developed by considering only the significant factors affecting pavement cooling.