ABSTRACT
ABSTRACT: Foaming of asphalt binders has become the most popular method for producing Warm-Mix Asphalt (WMA) in the United States. Mixing cold water and hot binder results in an expansion of the binder, a reduction in binder viscosity, and improved workability of the mixture and better coating of the aggregates by the foamed binder. The objectives of this study are to develop laboratory test methods to determine workability and coatability of asphalt mixtures and to validate the improved workability and coatability of foamed WMA as compared to Hot-Mix Asphalt (HMA). In the study, the maximum shear stress obtained during compaction using a Superpave Gyratory Compactor (SGC) is proposed as workability parameter. For mixture coatability evaluation, a testing procedure based on aggregate absorption is used and a coating parameter, coatability index, is proposed. Foamed WMA with different binder sources and grades and various water contents as well as control HMA are produced and evaluated in the study. Test results indicate that there is an optimum foaming water content that produces foamed WMA with the best workability and coatability characteristics when compared not only to other foamed WMA but also to control HMA.
