National Academies Press: OpenBook

Manual for Emulsion-Based Chip Seals for Pavement Preservation (2011)

Chapter: Chapter 9 - Performance

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Page 27
Suggested Citation:"Chapter 9 - Performance." National Academies of Sciences, Engineering, and Medicine. 2011. Manual for Emulsion-Based Chip Seals for Pavement Preservation. Washington, DC: The National Academies Press. doi: 10.17226/14421.
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Page 27

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27 9.1 Less Than One Year Performance during the very early life of the chip seal is judged based on chip loss or flushing. Chip loss can happen as soon as a few hours after removing traffic control. If the loss is greater than 10% of the applied chip quantity (assuming a one-layer chip application), the cause should be investigated. Often, early failures of this type are due to high chip applica- tion rates, low emulsion application rates, or both. Early chip loss can also be due to excess material passing the no. 200 screen, or aggregate not meeting gradation requirements. Unexpected low temperatures, wet weather, or opening to traf- fic before adequate residue adhesion has developed can cause early chip loss. Inundation of chips occurs because of high emulsion appli- cation rate, embedment of chips in the substrate, or both. Streaking or roping is caused by the spray bar on the as- phalt distributor being either too high or too low. Correction after construction is not possible without the application of another seal. 9.2 Greater Than One Year Performance after one year can be measured using texture depth. Some specifications (Austroads 2006) limit design life based on texture of less than 0.9 mm on pavements with speeds greater than 43 mph. The following relationship has been pro- posed as a means of predicting approximate texture after one year (Gransberg et al. 2005): Where Td1 = texture depth in 1 year, mm; Yd = design life in years; and ALD = average least dimension of the aggregate, mm. Texture depth is determined using sand patch or CT meter tests. If texture is less than the predicted value, the texture should be monitored to determine if a loss of texture beyond 0.9 mm is expected. Td ALD log Yd1 0 07 0 9= +. . C H A P T E R 9 Performance

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TRB’s National Cooperative Highway Research Program (NCHRP) Report 680: Manual for Emulsion-Based Chip Seals for Pavement Preservation examines factors affecting chip performance, highlights design and construction considerations, and explores procedures for selecting the appropriate chip seal materials. The report also contains suggested test methods for use in the design and quality control of chip seals.

Appendices A to J of NCHRP Report 680 provide further elaboration on the work performed in this project.

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