The effect of laboratory compaction method on the resilient behaviour and fabric of aggregate base course materials

Aggregate base course (ABC) layer is a key structural component of most pavements. The compaction of ABC is a crucial procedure affecting its mechanical performance. There are two different methods commonly used in the lab to compact ABC specimens: impact and vibratory. Past studies have demonstrated that the compaction method can affect the resilient deformation behaviour of ABC. However, the reasons for these differences in terms of the constituent ABC particle properties and the resultant compacted aggregate fabric remains unclear. This study evaluates the influence of the laboratory compaction method on the resilient behaviour and fabric of two ABC materials with differing mineralogies. Resilient modulus tests performed on the specimens compacted with the two methods result in different behaviours. A series of subsequent laboratory tests were performed to explain the observed resilient behaviour by assessing changes in aggregate morphology and fabric. The study presented herein incorporates digital imaging analyses using a novel specimen preparation technique. The results demonstrate that impact compaction can degrade ABC materials that are susceptible to crushing. This, in turn, increases the resilient modulus of the ABC by increasing the number of contact points between particles. It is recommended that the compaction method used in the laboratory match the compaction processes in the field as best as possible to obtain the most representative resilient modulus test results.