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6 difference in the adhesion of different classes of emulsions Emulsion Application Temperature to aggregates (Shuler and Lord 2009). However, the selec- Emulsion application temperature should be within a range tion of emulsion should take into consideration the environ- to provide uniform transverse and longitudinal spraying but mental conditions present during construction. For example, should not exceed 185F (85C). anionic emulsions break by evaporation so humid site con- ditions could lead to longer setting times for anionic com- pared with cationic materials. High float emulsions are a class 2.6 Construction Preparation of emulsion that can be either anionic or cationic and are for- Preparation of the pavement surface prior to chip-seal mulated with a gel structure to produce a thicker asphalt operations can influence performance of the chip seal. This coating on aggregate chips. Some high float emulsions con- preparation varies depending on the condition of the exist- tain oil distillates that increase setting time, so increased traf- ing pavement but at a minimum should include sweeping the fic control may be needed for these products. surface to remove loose debris, dust, or other contaminants. Viscosity Grade 2.6.1 Fog Seal Pre-Treatment of Substrate Emulsions are produced in two viscosity categories, desig- If the pavement surface is extremely dry or porous or there nated "-1" and "-2" for low and high viscosity, respectively. is possible loss of some of the chip-seal binder to the pavement, Because aggregate chips require approximately 40% initial a light fog seal application should be considered prior to chip embedment during construction, the high viscosity emul- sealing. Sometimes hot mix asphalt patches are needed to re- sions should always be used since the low viscosity emulsions pair the existing pavement prior to chip sealing. These patched would flow off the substrate. areas should be sprayed with a light fog seal prior to applying The viscosity of the emulsion during construction is an the chip seal since fresh hot mix asphalt can absorb the emul- important factor. Emulsions with too low viscosity could sion after chip sealing, resulting in significant loss of chips. flow off the pavement before the aggregate chips are embed- ded, resulting in a loss of chips under traffic and potential environmental issues. Emulsions with too high viscosity may 2.6.2 Repairs not provide adequate coating of the aggregate chips, leading Alligator cracking, potholes, failing patches, and active to a loss of chips. cracks greater than 1/4 in. in width should be repaired to pro- vide a stable surface for the new chip seal. Application Rate The binder application rate must be correct during con- 2.7 Maintenance struction to achieve optimum performance of the chip seal. Fog seals are often applied to a new chip seal to provide Too little emulsion will not retain chips in place under traf- additional binder and higher contrast for pavement strip- fic, and too much emulsion will lead to flushing and loss of ing paint. Care should be taken whenever applying a fog seal friction. The optimal application rate is a function of the vol- since pavement friction could be reduced if the fog seal is ume of voids in the compacted aggregate chip layer, the volume applied at too high an application rate, the fog seal emulsion and type of traffic, the pavement gradient, and the condition has a high residue content, or the fog seal has not broken of the substrate pavement. sufficiently to support uncontrolled traffic.