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13 Selecting the appropriate chip seal to use on a specific facil- ity is important. For example, a chip seal using 3â4-inch maxi- mum size aggregate may be appropriate for a rural farm-to- market road with 500 vehicles per day per lane but not for an urban street carrying 10,000 vehicles per day per lane. The fol- lowing discussion will provide information regarding the seal that is most appropriate for a given project. 4.1 Single Seal The single application chip seal is the most commonly used chip-seal process. These chip seals have been used with success on all pavement types. However, potential disadvantages, in- cluding vehicle damage, tire noise, and roughness, are reasons for considering variations from the single seal. In addition, the sealing ability of a single chip seal is limited based on chip size. An increase in chip size increases sealing ability because of the greater binder volume required to hold the stone in place, but it also increases the potential for the noted disadvantages. 4.2 Single Seal with Choke Stone This type of seal is a single chip seal with choke stone ap- plied to the chip seal prior to rolling. The choke stone should meet the same physical requirements of the chip-seal aggregate and the gradation shown in Table 7 when used with chip seals with aggregate maximum size exceeding 3â8 inch (9.5 mm). The choke stone helps lock the chip-seal aggregate in place and produces a surface that is less likely to produce dislodged larger chip-seal aggregates under traffic. It results in less risk of loose stones and a quieter and smoother surface. 4.3 Double Seal The double chip seal is used when pavement conditions 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 that of the second chip seal. In comparison to other seal types, double chip seals provide higher sealing capability, longer service life, less risk of dislodgement of the larger aggregates, smaller aggregate in contact with traffic and snow plows, and a quieter surface. However, double seals are higher in cost and require longer to construct. C H A P T E R 4 Selecting the Appropriate Chip Seal Sieve Passing, % ¼-inch 100 No. 4 85â100 No. 8 10â40 No. 40 0â5 No. 200 0â1 Table 7. Example of choke stone gradation.