The method of laboratory compaction influences the mechanical properties of asphalt specimens. Hence in selecting a compaction method, factors such as the ease, the cost of specimen production and the ability to represent field compaction are considered. Among the different compaction methods, slab compaction is recognized for its considerable similarity to field compaction. On the other hand, the simplicity of preparing specimens using impact compaction method has led to its widespread use despite its failure to simulate field compaction. The goal of the present study was to compare the properties of specimens prepared by impact and slab compaction. The study specifically aims to determine the shift factors that can be used to relate the properties of impact compacted specimens with specimens prepared by slab compaction. The differently compacted specimens were fabricated with identical geometric and volumetric characteristics using two types of mixtures. Properties investigated included the marshall stability and flow, the dynamic stiffness and the resistance to permanent deformation. The permanent deformation behavior and the stiffness of the specimens were evaluated under variable conditions using uniaxial cyclic compression tests. Results showed that the two compaction methods produced specimens with widely varying mechanical properties. Impact compaction was found to produce specimens that were stable and more resistant to permanent deformation than those produced by slab compaction. Specimens produced by impact compaction were also observed to be stiffer. The comparison of the specimens’ properties revealed the shift factors that can be used to accurately translate the properties of impact compacted specimens to those observed in slab compacted specimens. Shift factors are recommended when using impact compacted specimens in performance related testing of asphalt mixtures. The shift factors may enable the impact compaction method to more closely represent field conditions.

asphalt, impact compaction, slab compaction, permanent deformation, compaction shift factor