Asphalt Concrete Field Compactibility Models Focusing on Aggregate Properties and Moisture

Some aggregates used in asphalt production retain fine dust coatings after crushing and washing operations, and these coatings, especially when coupled with moisture, can be severe enough to cause asphalt mixture tender-zone characteristics. This paper's objective was to investigate asphalt mixture field compactibility by focusing on aggregate properties (e.g., moisture content and dust coating). In cooperation with the Mississippi Department of Transportation (DOT), 12 asphalt mixtures and 44 test locations were selected and studied. Considered for selection were mixtures with which the Mississippi DOT had experienced tenderness issues that were thought to be related to aggregate-adhered fines or aggregate moisture. Field compactibility was investigated with multiple regression procedures where air void (Va) level was the selected response variable. For each paving project, 31 material, production, and construction properties were collected for consideration within regression models. Through screening and processing procedures, the set of properties was refined to develop three regression models with R2 values ranging from .74 to .86. These models incorporated terms for fine aggregate angularity (FAA), surface area of coarse aggregate (SA8), cold-feed aggregate methylene blue value (MBVCF), cold-feed aggregate moisture (wCF), and other mixture properties (e.g., asphalt content and lift thickness). Key findings were the following: aggregate-adhered fines (ASTM D5711) and FAA had no effect on Va; increasing wCF slightly negatively affected Va; and increasing MBVCF positively affected Va. In general, aggregate property effects on Va were less meaningful than other properties included (e.g., lift thickness). Overall, regression models could be valuable to agencies and contractors for general guidance regarding factors affecting Va.