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

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Bituminous Pavement Stripping Research Findings City of Ramsey January 16, 2020 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 with a CSS-1h diluted to one part water and one part emulsion. • 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 both the paving contractor and paving materials. While many city and county engineers were able to provide valuable detail on their chip -sealed roads for this study, the results and conclusions were limited by a lack of information (see Section 3.4). Detailed records of contractor and materials would benefit future research efforts and municipal efforts to maintain roads. • NS462 — Is Seal Coating Counterproductive or Not? o Study not yet complete. Page 2 of 2