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7 CHAPTER 3 Design and Construction Considerations Before a chip seal can be designed, there are certain factors 3.2.4 Fog Seal Applied to Chip Seals that must first be known about the project. The first part of this process involves selecting the pavement to chip seal. The A fog seal may be applied to a fresh chip seal to provide second part is selection of the type of seal to be placed. slightly more asphalt to account for possible deficiencies in emulsion application rate, to provide a higher contrast between 3.1 Identifying Appropriate pavement markings and the surrounding surface, and to pro- Pavements to Chip Seal vide possible improved cracking performance. Care should be taken whenever applying a fog seal since pavement fric- Chip seals are most effective for pavement preservation tion could be reduced if the fog seal is applied at too high an when applied to pavements with limited or no distress (i.e., application rate, the fog seal emulsion has a high residue con- cracking has not begun or is less than 1/8-in. wide, rutting is tent, or the fog seal has not broken sufficiently to support less than 3/8 in., and structural distress is isolated with low- uncontrolled traffic. severity fatigue). Pavements with severe cracking and rutting may require multiple patches and crack sealing prior to chip 3.3 Chip Seal Selection sealing. In general, pavements in poor condition will achieve shorter service lives than pavements in good condition. The type of chip seal used depends on many factors. Under high traffic volumes, double seals or seals with choke stone 3.2 Type of Seal have lower potential for chip loss and vehicle damage. Dou- ble and choke stone seals should provide less tirepavement The types of chip seal include single, double, and single noise due to smaller aggregate size. The life expectancy of dou- chip seal with choke stone; any of these chip seals may have a ble seals and seals with choke stone should be higher and the fog seal applied afterward. sealing ability should also be greater than single seals under the same conditions. However, the cost of double seals is obvi- 3.2.1 Single Chip Seal ously higher. A single chip seal consists of a spray application of asphalt emulsion followed by an application of aggregate chips, prefer- 3.4 Selecting the Aggregate Size ably one stone layer thick. The chip seals described in this manual are single chip seals consisting of one application of asphalt emulsion and one 3.2.2 Double Chip Seal layer of aggregate chips. The gradation of the chips should A double chip seal is two applications of a single chip seal. consist of one or two consecutive sieve sizes with little or no The first chip seal is constructed with aggregate one sieve size material passing the 0.075-mm sieve (no. 200). The maximum larger than the second chip seal. aggregate size in the chip seal influences the performance of the chip seal. Larger aggregates provide greater sealing per- formance because of the higher asphalt volume needed to 3.2.3 Single Chip Seal with Choke Stone retain the chips in place. However, larger aggregates produce This type of seal is a single chip seal but with crushed fine more traffic noise, have rougher texture, and have greater po- aggregate applied to the surface of the chip seal prior to rolling. tential to damage vehicles. These advantages and disadvantages