Vibratory Compaction of Base Course Aggregates

The focus of this paper is on laboratory compaction of unbound granular base course material for road pavement construction. The primary variables evaluated in this research were particle size distribution and dry density. This research addresses the applicability of current laboratory compaction techniques and outlines the changes needed to minimize the gap between laboratory and field compaction. The target density achieved in laboratory studies with the New Zealand standard test methodology, which is then used to target field compaction levels, is often too high to realistically achieve in the field. It was found that there is a ratio of maximum aggregate average least dimension (ALD) to specimen diameter and specimen height that must be adhered to when using laboratory testing as a means to evaluate, design, or construct pavement base course layers. In addition, the power input of laboratory vibratory hammers used for compaction must be controlled to minimize aggregate degradation, especially for test molds that do not satisfy the minimum diameter to ALD ratio. The ultimate goal of laboratory compaction should be to accurately simulate field compaction and provide realistic targets that can be achieved in the field. If unrealistic field compaction density targets are specified, then overcompaction can occur and cause aggregate breakdown. The research concluded that changes are required for test standards to better reflect field conditions, such as less lateral constraint, and better reflect achievable target field densities.