Alaska's Dense-Graded High-Float Emulsion Surface Treatments: A New Mix Design

Asphalt surface treatment (AST) pavements using high-float (HF) emulsions and dense-graded aggregates have been constructed on Alaska's low-volume roads for more than 20 years. These HF ASTs proved to be relatively inexpensive, were easy to construct, and provided good service for low-volume roads. However, the normally positive economics of these pavements have sometimes been offset by problems during or after construction. It was argued that most problems could be solved if a mix design method was devised to ensure optimum application rates of emulsion and aggregate. This paper presents a standardized laboratory mix design method for HF emulsion and dense-graded aggregates based on simple volumetric calculations. The method accounts specifically for aggregate maximum size, compaction characteristics, moisture content, and air voids. An outline of the design method and an example numerical application are presented, and reasons supporting each element of the design method are discussed. The paper addresses the variables that control the emulsion and aggregate contents of these mixes. New laboratory test methods are proposed for determining aggregate density. The proposed mix design method requires that 15% additional aggregate be added to the design amount determined through voids calculations. The paper also presents information that improves the constructability and long-term performance of HF pavements.