Understanding the Effects of Aggregate and Emulsion Application Rates on Performance of Asphalt Surface Treatments

Abstract

Presented are the effects of aggregate and emulsion application rates on the performance of asphalt surface treatments (ASTs), as evaluated by the third-scale Model Mobile Loading Simulator (MMLS3) and digital image processing. Performance characteristics evaluated in this study include aggregate loss and bleeding. Lightweight aggregate and granite aggregate with different gradations were used with CRS-2 emulsion to design the various combinations of aggregate and emulsion application rates. The MMLS3 test protocol was applied to these AST specimens, and performance measurements were analyzed as a function of the application rates. Results demonstrated that the new AST performance test method introduced in this study was an excellent means of evaluating AST performance. It was found that the major factor affecting AST performance was aggregate gradation. Also, a method was developed to determine the optimum aggregate and emulsion application rates from the MMLS3 test results. The optimum rates determined from this method were confirmed by a blind test performed by bituminous supervisors and road maintenance unit engineers at the North Carolina Department of Transportation. Finally, results from this study were used to study the voids concept, which serves as the foundation for AST mix design. It was concluded that the reference voids (the compacted voids resulting from MMLS3 trafficking) depend on the voids in the loose aggregate that are, in turn, affected by the aggregate gradation type.