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The state of Washington is divided by the Cascade Mountains into mild and moist coastal plains to the west and a much drier and seasonally hot and cold plateau to the east. Data based on experience in the state are presented to show that the design of a bituminous mix for maximum serviceability should be tempered to a considerable extent by its climatic environment and that the stabilometer, cohesiometer, and kneading compactor are useful tools in providing desirable design versatility. Densities obtained with the kneading compactor compare favorably with densities developed in the roadway after one or more years of service. Further data show that the density of a bituminous pavement generally decreases with depth and that the kneading compactor prepares a specimen with similar density distribution. Case histories of several selected bituminous pavements are presented and show that their service characteristics, particularly as related to plastic deformation, were forecast accurately by the stabilometer and cohesiometer. In conclusion, data are presented indicating that the following factors influence the serviceability of heavy-duty bituminous pavements: climatic environment of the pavement; quantity of asphalt; amount and type of dust; ratio of dust to sand; stabilometer and cohesiometer values of the mix; and weather conditions at time of placing. Where applicable, limiting numerical values for these various factors are suggested.
Minor, Carl E.
Materials and Research Engineer, Washington State Highway Commission, Olympia, Wash.