Asphalt Binder Contribution to Mixture Workability and Application of Asphalt Lubricity Test to Estimate Compactability Temperatures for Warm-Mix Asphalt

The disconnect between estimated compaction temperatures on the basis of viscosity and behavior observed in laboratory- and field-compacted mixes indicates that the sole use of viscosity is insufficient to characterize the role of the asphalt binder in mixture compaction. The asphalt lubricity test was presented as a complement or replacement to viscosity on the basis of the concept that it was necessary to measure the properties of binders in thin films to relate better to compaction of mixes and to detect the effects of warm-mix asphalt (WMA) additives. To assess the value of the asphalt lubricity test, the relative contributions of lubricity, viscosity, and aggregate gradation on mixture workability at different levels of compactive effort were studied with statistical analysis. The mixes included fine and coarse gradations prepared with various conventional and WMA-modified binders, compacted at a range of temperatures representative of those used for WMA. Results indicated that gradation and binder lubricity contributed significantly to mixture workability at conditions of lower temperature, lower density, or both. The effects of viscosity were found to be insignificant. Aggregate gradation was found to be the most influential factor, which indicated that, for some mixes, use of WMA additives was not always necessary to improve laboratory compaction. To support selection of compaction temperatures on the basis of binder properties, a method was presented to apply the asphalt lubricity test to estimate minimum WMA compaction temperatures.