Performance-Related Specifications for Asphalt Emulsions Used in Microsurfacing Treatments

This paper details the development of a framework for emulsion performance grade (EPG) specifications for microsurfacings. Microsurfacings are preservation surface treatments designed to improve the condition of the pavement surface while mitigating deterioration of the overall pavement structure. Asphalt emulsions used in microsurfacings are often selected on the basis of factors that are not necessarily related to performance. Rutting and thermal cracking have been identified as the most critical microsurfacing distresses related to binder performance. In the assessment of fresh emulsion properties, storage stability and mixability have been determined to be the most critical constructability concerns. For this study, binder and mixture test methods were identified to reflect the failure mechanisms for each critical distress type. The two emulsion residue test methods that were identified to capture microsurfacing performance were (a) the multiple stress creep and recovery test for rutting and (b) the dynamic shear rheometer frequency sweep test for thermal cracking. The identified critical fresh emulsion properties that related to constructability included storage stability and viscosity measured at a low shear rate. The proposed EPG specifications for fresh emulsion properties related to constructability were developed by using statistical analysis of the binder test results. The EPG specifications for residual binder were developed by defining the temperature-independent relationships between the emulsion residue properties and the mixture performance that corresponded to each critical distress. Preliminary specification limits were then established on the basis of the values of the binder properties that corresponded to the critical mixture performance thresholds.