United States Department of Transportation
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Abstract:The objective of this study was to evaluate in-place pavements experiencing rutting and pavements experiencing no rutting to begin to classify asphalt mixtures that should perform satisfactorily and those that would likely rut under traffic. The information reported herein is part of a larger study to evaluate rutting in the field and in the laboratory and to develop information that would insure improved performance. This report summarizes the work accomplished during the first 1-1/2 years of the study. The entire study is projected to continue for a total of five years. Five pavements were selected for analysis; four of the pavements had been identified as experiencing premature rutting and one pavement had been identified as having no rutting after more than 10 years of service. Rutting measurements were taken across the outside traffic lane and a trench was cut across the lane for each of the highways experiencing rutting. The trench was closely investigated to determine the extent of rutting in each layer of asphalt mixture. Cores were taken at approximately one foot intervals across the pavement lane, transported back to the laboratory, and analyzed to determine material and mixture properties. Laboratory tests included asphalt content, aggregate gradation, and analysis of in-place and recompacted mixture properties. Results of this study show that the pavements that had rutted under traffic in most cases appeared to have rutted due to low air voids (in recompacted samples and/or in the field). The Gyratory Shear Index (GSI) determined during compaction with the Gyratory Testing Machine was shown to be a good indicator of mixes that had rutted under traffic. Based on the results of this study, a maximum GSI value of 1.1 is recommended when compacting samples with 1 degree angle, 120 psi, and 300 revolutions. The Marshall flow appears to be a good indicator of rutting potential. Mixes having flow values above 16 tended to have higher amounts of rutting. The resilient modulus and indirect tensile strength values were found to be not significantly related to rutting. Most of the rutting observed in this study had occurred in the top layers of asphalt concrete. These layers often contained fine aggregate gradations and high asphalt contents. 7 Tables, 21 figures. 46 p.
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