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13 CHAPTER 4 Selecting the Appropriate Chip Seal Selecting the appropriate chip seal to use on a specific facil- Table 7. Example ity is important. For example, a chip seal using 3/4-inch maxi- of choke stone mum size aggregate may be appropriate for a rural farm-to- gradation. market road with 500 vehicles per day per lane but not for an Sieve Passing, % urban street carrying 10,000 vehicles per day per lane. The fol- -inch 100 lowing discussion will provide information regarding the seal No. 4 85100 No. 8 1040 that is most appropriate for a given project. No. 40 05 No. 200 01 4.1 Single Seal The single application chip seal is the most commonly used The choke stone helps lock the chip-seal aggregate in place chip-seal process. These chip seals have been used with success and produces a surface that is less likely to produce dislodged on all pavement types. However, potential disadvantages, in- larger chip-seal aggregates under traffic. It results in less risk cluding vehicle damage, tire noise, and roughness, are reasons of loose stones and a quieter and smoother surface. for considering variations from the single seal. In addition, the sealing ability of a single chip seal is limited based on chip size. 4.3 Double Seal An increase in chip size increases sealing ability because of the greater binder volume required to hold the stone in place, but The double chip seal is used when pavement conditions it also increases the potential for the noted disadvantages. require substantially higher sealing ability, such as for facili- ties with higher traffic volume. The first chip-seal application uses a maximum size aggregate that is one sieve size larger than 4.2 Single Seal with Choke Stone that of the second chip seal. In comparison to other seal types, This type of seal is a single chip seal with choke stone ap- double chip seals provide higher sealing capability, longer plied to the chip seal prior to rolling. The choke stone should service life, less risk of dislodgement of the larger aggregates, meet the same physical requirements of the chip-seal aggregate smaller aggregate in contact with traffic and snow plows, and and the gradation shown in Table 7 when used with chip seals a quieter surface. However, double seals are higher in cost and with aggregate maximum size exceeding 3/8 inch (9.5 mm). require longer to construct.