Effect of mixture compaction on indirect tensile stiffness and fatigue

When constructing laboratory samples of bituminous mixture that are intende d to have the same characteristics as the in situ pavement layer, the most important factor to consider is compaction. It is widely accepted that diff erent laboratory compaction methods produce samples with different orientat ions and distributions of aggregates, and different distributions and shape s of voids. The effect of different laboratory compaction procedures (namel y, roller, Marshall, vibrating hammer, and gyratory techniques) on the indi rect tensile stiffness and fatigue properties of two standard Irish bitumin ous mixtures (namely, hot-rolled asphalt and dense base coarse macadam) was investigated. The roller compaction method produced specimens of lower sti ffness, similar to site compacted samples. The influence of the compaction method on the fatigue strength of asphalt mixes would appear to be mixture dependent; mixes with grading profiles that are designed for aggregate inte rlock were found to have higher fatigue strengths, provided the material wa s compacted using a method that would facilitate reorientation of the aggre gates.