Relationships Between Laboratory Measured Characteristics of HMA and Field Compactability (With Discussion)

Field compaction has become a greater challenge since the increased use of polymer modified binders and introduction of Superpave designed mixtures. Compacting difficulty has been cited for many Superpave designed mixes, meaning that to achieve acceptable density levels, a greater compactive effort is required. Laboratory measured mixture parameters have been proposed as HMA compactability indicators by several asphalt researchers. However, actual field studies have not validated most of these measured. In this study, laboratory parameters used as mix compactability measures are compaction slope, locking point, and Bailey Method ratios, number of gyrations to reach 92% of G sub mm (N sub 92), percentage of G sub mm at N sub ini, and Compaction Energy Index, whereas in the field, mix compactability is quantified by the Accumulated Compaction Pressure. Results show that many factors affecting field compaction complicate finding a simple laboratory and field compactability relationship, and thus the relationship between laboratory compactability and field compactability could not be described by a single correlation. However, a relationship was established through multiple regression analysis.