Aggregate interlocking of open-graded friction courses with compaction effort

Densification of open-graded friction course (OGFC) makes it inefficient, with the reduction of air void content due to aggregate breakage by over compaction efforts. Therefore, it is important to identify the optimum compaction effort to accomplish the most stable aggregate on aggregate contact of internal aggregate structure with increasing compaction. This paper presents the optimum number of gyrations that would be needed for aggregate locking. Samples were prepared with various gradations, binder contents and compaction levels to compare different combinations of these conditions on the optimum compaction. The aggregate interlocking point was found using two methods; (a) by observing height variation of the sample and (b) by calculating the gradient of height variation curve generated by superpave gyratory compactor (SGC). According to method (a) aggregate interlocking point was identified and it was observed that compaction effort increases with coarser mixtures. As per method (b), the calculated interlocking point, which was independent from individual variations was found proximate to 50 gyrations as an average among all samples under various gradations, binder contents and compaction levels. Both methods provided compaction results greater than 85 % of the maximum theoretical density at the interlocking point. The results concluded that the gradient calculation method can be adopted successfully as an unbiased method to find the aggregate interlocking point of OGFC samples to determine the optimum compaction level.