Laboratory investigation of asphalt pavements with low density and recommendations to prevent density deficiency

In most USA asphalt construction projects the goal of compacting a hot-mix asphalt (HMA) layer is to achieve the optimum density which is 92% of the maximum specific gravity (G_mm) of the asphalt mixture. However, this level of density is not always achieved. This paper evaluates the effect of field compaction deficiencies on the HMA durability through laboratory testing. HMA samples were collected from construction sites in the United States. A series of laboratory tests were conducted to compare the performance of HMA mixtures at their actual in-place density as well as the desired density of 92% of G_mm. The statistical analysis on the results showed that the performance of the pavements could significantly improve by eliminating the deficiencies in their in-place densities. Moreover, the compactibility of the mixtures was investigated using the compaction data from the Superpave gyratory compactor. Compaction characteristics of the mixtures were compared to a control mixture, and the results showed that the shortage in the binder content of the mixtures could be a major factor which may have caused the density deficiencies. Furthermore, the effect of higher-than-optimum binder content was evaluated on the compactibility of the control mixture.