Effect of Particle Shape on Durability and Performance of Unbound Aggregate Base

AbstractEffects of particle shape on the durability (as determined from micro-Deval test) and performance [as determined from resilient modulus (MR), and permanent deformation (PD) tests] of unbound aggregate base (UAB) used in road structures have been evaluated in detail. Four crushed aggregates with different mineralogy (but similar angularity) were selected, and each aggregate type was mixed based on varying particle shapes (ranging from flat to equidimensional) to create dense- and open-graded gradations. The findings showed that the increase in flatness ratio affects the compaction and interlocking characteristics of the open-graded UAB materials much more than the dense-graded UAB materials. For open-graded UAB samples, the MR of the aggregates, regardless of the mineralogy, increased with increasing flatness ratio. The MR values of the dense-graded aggregates had an observed peak value at a flatness ratio of 0.6, whereas the final permanent strain during PD testing increased with increasing flatness ratio at the higher stress conditions tested. The effect of the particle shape was modeled using the MEPDG model, and the results showed that particle shape may have an effect on the overall performance.