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Bituminous Pavement Stripping Research Findings <br /> City of Ramsey <br />February 13, 2020 <br />Local Road Research Board (LRRB) Pavement Stripping Research Conclusions and Recommendations <br />2013-08 Stripping of Hot-Mix Asphalt Pavements under Chip Seals (Wood & Cole, MnDOT) <br /> <br />Conclusions: Stripping of HMA pavement after application of chip seal caused by areas <br /> <br />o <br />of high air voids or low density. <br />Recommendations:Agencies should use specified density methods to ensure proper <br /> <br />o <br />uniform compaction of HMA paving. Three options for addressing existing streets with <br />low density and high air voids variability include: <br />1.Do nothing and allow pavement to fail prematurely. <br /> <br />2.Chip seal early in pavement life, preferably within first 4 years, to keep <br /> <br />pavement structure as dry as possible to limit moisture damage. <br />3.Fog seal pavement with a CSS-1h diluted to one part water and one part <br /> <br />emulsion. <br />2017-35 Prevention of Stripping Under Chip Seals (David L. Rettner, AET) <br /> <br />Conclusions: <br /> <br />o <br />1.Study could not verify conclusions of 2013 LRRB research that high air voids is <br /> <br />the primary cause of stripping (Wood & Cole, 2013). <br />2.Study unable to identify mix designs or construction practices that correlated <br /> <br />with incidence of stripping (e.g., bituminous mixture, contractor, geographic <br />location, or year of construction). <br />3.Primary conclusion of study is that while stripping under chip seals is a concern, <br /> <br />it cannot be addressed with a simple mix design or paving rule of thumb. <br />Recommendations: <br /> <br />o <br />1.Stripping under chip seals may be due to trapped moisture and water vapor <br /> <br />between the chip seal and the asphalt pavement. This phenomenon would be <br />similar to stripping behavior observed in conventional overlays of asphalt <br />(Kandhal & Rickards, 2001). <br />2.Ensure appropriate drainage in chip-sealed pavements. Utilization of subsurface <br /> <br />drainage will reduce the probability of saturated subbase and base layers, which <br />will reduce the amount of moisture moving through pavement. <br />3.Minimize trapped water vapor between chip seal and the underlying asphalt. If <br /> <br />first lift of pavement is damaged due to insufficient structural capacity to <br />withstand heavy loads, the pavement may already have significant microscopic <br />sized cracks that allow water vapor to be transmitted from subgrade soils into <br />the pavement and be trapped. Causes of this cracking can include staggered <br />construction of bituminous pavement layers across multiple construction <br />seasons subjecting pavement to heavy loads while not at full strength. <br />4.Explore use of thin bituminous overlays, approximately five-eighths inches in <br /> <br />thickness, as an alternative to chip seal treatments. In Texas, these fine-mix <br />overlays have shown promise as a surface treatment on oxidized pavement and <br />as a surface treatment to extend the life of roadways exhibiting signs of <br />stripping. Studies have shown these thin overlays can extend the service life by <br />an additional three to five years before a mill-and-overlay is required. <br />5.Maintain better municipal records on both the paving contractor and paving <br /> <br />materials. While many city and county engineers were able to provide valuable <br />detail on their chip-sealed roads for this study, the results and conclusions were <br />limited by a lack of information (see Section 3.4). Detailed records of contractor <br />and materials would benefit future research efforts and municipal efforts to <br />maintain roads. <br />Page 2 of 3 <br /> <br /> <br />