Agenda - Council - 02/24/2020 - Laserfiche WebLink

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Bituminous Pavement Stripping Research Findings City of Ramsey February 20, 2020 Local Road Research Board (LRRB) Pavement Stripping Research Conclusions and Recommendations • LRRB 2013-08 Stripping of Hot -Mix Asphalt Pavements under Chip Seals (Wood & Cole, MnDOT) o Conclusions: Stripping of HMA pavement after application of chip seal caused by areas of high air voids or low density. o Recommendations: Agencies should use specified density methods to ensure proper uniform compaction of HMA paving. Three options for addressing existing streets with low density and high air voids variability include: 1. Do nothing and allow pavement to fail prematurely. 2. Chip seal early in pavement life, preferably within first 4 years, to keep pavement structure as dry as possible to limit moisture damage. 3. Fog seal pavement w/ CSS-1h diluted to one -part water and one -part emulsion. • LRRB 2017-35 Prevention of Stripping Under Chip Seals (David L. Rettner, AET) o Conclusions: 1. Study could not verify conclusions of 2013 LRRB research that high air voids is the primary cause of stripping (Wood & Cole, 2013). 2. Study unable to identify mix designs or construction practices that correlated with incidence of stripping (e.g., bituminous mixture, contractor, geographic location, or year of construction). 3. Primary conclusion of study is that while stripping under chip seals is a concern, it cannot be addressed with a simple mix design or paving rule of thumb. o Recommendations: 1. Stripping under chip seals may be due to trapped moisture and water vapor between the chip seal and the asphalt pavement. This phenomenon would be similar to stripping behavior observed in conventional overlays of asphalt (Kandhal & Rickards, 2001). 2. Ensure appropriate drainage in chip -sealed pavements. Utilization of subsurface drainage will reduce the probability of saturated subbase and base layers, which will reduce the amount of moisture moving through pavement. 3. Minimize trapped water vapor between chip seal and the underlying asphalt. If first lift of pavement is damaged due to insufficient structural capacity to withstand heavy loads, the pavement may already have significant microscopic sized cracks that allow water vapor to be transmitted from subgrade soils into the pavement and be trapped. Causes of this cracking can include staggered construction of bituminous pavement layers across multiple construction seasons subjecting pavement to heavy loads while not at full strength. 4. Explore use of thin bituminous overlays, approximately five -eighths inches in thickness, as an alternative to chip seal treatments. In Texas, these fine -mix overlays have shown promise as a surface treatment on oxidized pavement and as a surface treatment to extend the life of roadways exhibiting signs of stripping. Studies have shown these thin overlays can extend the service life by an additional three to five years before a mill -and -overlay is required. 5. Maintain better municipal records on paving contractors and paving materials. While many city/county engineers were able to provide valuable detail on their chip -sealed roads for this study, the results and conclusions were limited by lack of information (see Section 3.4). Detailed records of contractor and materials would benefit future research efforts and municipal efforts to maintain roads. • LRRB NS462 — Is Seal Coating Counterproductive or Not? o Study not yet complete. Page 2 of 2