Influence of aggregate type and gradation on voids of asphalt concrete pavements

Air voids in an asphalt concrete pavement highly influence its performance. Careful consideration of void requirements in compacted bituminous mixtures is more important than stability consideration, since the latter is always higher than necessary. Lack of attention to void requirements may be a direct cause of instability of asphalt concrete pavements. The present work studied the influence of aggregate type and its gradation on the voids in mineral aggregate and air voids of asphalt concrete paving mixtures as compacted according to the Marshall method. Three types of aggregates and five different gradations were employed. Aggregate gradation may be used to control the void requirements in a specific asphalt concrete mixture, influencing and/or affecting other important engineering properties such as water permeability of that specific mixture. On the other hand, aggregate type can provide the necessary voids requirements for an aggregate-asphalt mixture without sacrificing other important engineering properties. Two of the aggregates easily satisfied the void requirements. The third aggregate could not satisfy the same void requirements unless a porous gradation was used. Porous mixtures have more air voids, resulting in an increased permeability to water. This increase in permeability is not the same for different aggregate gradations. The coarser the mix, the higher the rate of increase in the water permeability for the same type of aggregate.