Influence of Aggregate Gradation and Degree of Compaction on Air Voids in Bituminous Concrete Mixes

The amount of air void influences the performance of bituminous mixes. The arrangement of aggregates is instrumental in understanding the framework of air voids. So, it becomes essential to study the particle size distribution of aggregates and compaction effort given in the preparation of the mix. Literature suggests that the aggregate properties, such as size, shape, and strength, have been studied to enhance the amount and distribution of air voids. The aim is to focus on the combined effect of aggregate gradation and compaction effort on the variation of air voids in bituminous concrete mixes. In this study, aggregates from two different sources namely Sheikhpura (Sh) and Mirza Chowki (Mc) is taken into consideration. Samples with varying gradation types were prepared under the same compaction effort and air voids corresponding to the mix of each gradation type were calculated. Now, samples are prepared by varying the compaction effort to each gradation type and air void is calculated. The observation suggests a significant reduction in air voids due to the initial increase in number of blows and this reduction in air void saturates at higher no. of blows and a comparatively lesser amount of air voids is found in denser gradation of aggregates. Mixes prepared with aggregates from Mc had comparatively lesser air voids for similar compaction efforts. The results are attributed to shape of Mc aggregates, due to which it breaks down upon compaction, resulting in a higher proportion of fine particles and reduced air voids for similar compaction efforts.