Evaluation of hot mix asphalt (HMA) lift thickness.
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2009-10-01
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Edition:Final report; Jan. 7, 2007-Dec. 31, 2008.
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Abstract:The range of lift thicknesses allowed by the Mississippi Department of Transportation has worked well for many years. However, because of the current availability of gravels of sufficient size to crush, modification to the allowed lift thicknesses amy be warranted. Therefore, the objective of this project was to evaluate the influence of lift thickness on the ability to achieve a desirable density with a reasonable compactive effort.
The research approach under taken to achieve the project objective was to conduct a detailed field study. A total of ten field projects were utilized in this study. At each of the field projects, the field compaction process was monitored and field date obtained. Data obtained from the field projects included four different mat temperature measurements over time, mat density after each pass of the roller suing a nuclear gauge, and final density and thickness obtained form cores. Cores cut from the roadway were also brought back to the laboratory for permeability testing.
Based upon analyses conducted on the data, several conclusions were drawn. The thickness of the placed layer does affect the amount of time that an HMA layer will remain at compaction temperatures. Thicker lifts will maintain temperature longer. Lift thickness did have an affect on the final in-place density. As lift thickness increased, final in-place density also increased. No impact related to lift thickness was found for density gradients within field compacted layers. Finally, there did not appear to be an influence of thickness on the permeability of HMA layers. Based upon these conclusions, new allowable lift thickness limits were recommended.
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