Abstract
An emphasis on environmental stewardship has prompted the use of warm-mix technologies aimed at allowing for production of conventional asphalt mixtures at reduced temperatures. Successful use of warm-mix asphalt (WMA) in field demonstrations has created a need for development of mix design procedures. A major impediment in development of these procedures is the evaluation of the effect of WMA technologies on asphalt binder and mixture workability. The objective of this study was to introduce a new test methodology for estimating asphalt binder workability by measuring the lubricity effects of a surfactant-based additive as well as binder foaming processes through novel use of the dynamic shear rheometer with a new testing fixture. The new test allows measuring the coefficient of friction of binders at various temperatures, loading rates, and normal force. Asphalt binder lubricity measurements were correlated mixture to workability tests defined by the compactive effort required to densify a mixture to 8% air voids. Mixture testing was conducted at temperatures ranging from 90 degrees C to 135 degrees C. Results of asphalt binder workability testing demonstrated a significant reduction in coefficient of friction due to the use of a surfactant-based WMA additive and identified a need for revised procedures for evaluation of foamed asphalts. Both warm-mix processes demonstrated enhanced mixture workability relative to the hot-mix asphalt; however, significant differences were not realized until compaction temperatures were below those normally used in production.