Assessment of Workability and Compactability of Warm-Mix Asphalt

One of the main benefits advertised about the use of warm-mix asphalt is the increased workability at conventional and lower compaction temperatures. From a field perspective, “workability” is commonly defined as the asphalt mixture property that describes the ease with which the asphalt mixture can be placed, worked by hand, and compacted to the desired mat density. Unfortunately, a laboratory property and test condition have yet to be developed to quantify these field characteristics. A research effort to evaluate the workability and compactability of different warm-mix additives preblended in a polymer-modified asphalt binder at varying percentages is summarized. Different test procedures, both asphalt binder related and asphalt mixture related, were evaluated and compared. Test results indicated that conventional mixing and compaction temperature asphalt binder tests were insensitive to the different warm-mix additives and dosage rates. Compaction data obtained with the gyratory compactor also indicated the device was generally insensitive to workability and compactability. Meanwhile, the University of Massachusetts workability device and the Marshall compaction hammer were found to rank the general workability and compactability of the mixtures in a rational order and compared favorably with one another. Not only was a promising new asphalt binder test, the lubricity test, sensitive to dosage rate and warm-mix additive, but the ranking compared favorably with mixture tests. The hope is that the information in this research effort can help in the selection and validation of warm-mix additives as a compaction aid.