Density Changes in Asphalt Pavement Core Samples

A loss in density with time was observed on a large number of cores taken from experimental pavement sections made with a Corps of Engineers type asphaltic concrete. This change is rapid and can account for significant differences in results between laboratories. On other mixes, there is an increase in density. The change, therefore, is not predictable and is different with the different aggregates and mix designs used. Some of the change appears to be caused by a slow gain or loss in weight, presumably water. The rest of the change is caused by an increase or decrease in calculated volume of the specimen. This observation offers a basis on which to devise a more reliable procedure for determining the density of asphalt concrete pavements. It also questions the basis on which relative density requirements are set.