Agenda - Council - 02/11/2020 - Laserfiche WebLink

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EXECUTIVE SUMMARY The Minnesota Department of Transportation (MnDOT) recently conducted a study that identified less dense areas, or high air voids, in underlying asphalt pavements as the main cause of stripping under chip seals (Wood & Cole, 2013). This research project follows the work of MnDOT with extensive testing and analysis of low -volume roads in Minnesota that have experienced stripping under chip seal surface treatments. The project focus was on 18 chip -sealed roadways in eight cities and counties in Minnesota. The research team evaluated the in -situ roads and collected pavement samples for laboratory tests. The research conducted included field studies of pavement distress and density (using ground -penetrating radar and nuclear gauge tests) and laboratory tests for permeability, stripping, tensile strength ratio, asphalt film thickness, and mix properties. A major outcome of the research is that the research was unable to verify the earlier finding that high air voids were a cause of stripping under chip seals. For those locations that did exhibit stripping, the test data did not support a direct relationship between asphalt pavement density and stripping. In addition, the research did not determine a direct relationship between incidence of stripping and site/supplier data (e.g., bituminous mixture, contractor, geographic location, or year of construction). This observation agreed with observations made by Minnesota city/county engineers. Other observations from 129 municipal engineers in Minnesota were obtained through an eight - question survey. The survey found that 64 percent of the respondents used chip -seal treatments on a regular basis. Of that fraction, 26 percent reported stripping in chip -sealed pavements as a major issue, 39 percent reported observing stripping but did not perceive it as a major issue, and 35 percent reported that they did not observe stripping in their chip seals. Given the survey and field data results, it is clear that not all roads with chip seals exhibit stripping. Finally, an additional outcome of the research is the large amount of testing data developed under the project work. This data, which is documented fully in appendices to the final report, will help support and improve future research on stripping in chip seals in Minnesota and chip seal performance in general.