413.9 Fly Coating

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Maintenance Planning Guideline for Fly Coating

Fly coating may be done on dry oxidized blade laid bituminous surfaces as needed. The annual program should probably not exceed 10-15% of the total low type bituminous mileage. Fly coating of machine laid decks must be approved by the Maintenance Division and are normally not allowed due to the loss of skid resistance.

The purpose of a fly coat is to add asphalt around the aggregate, in the voids and in small cracks. This should waterproof and extend the life of most surfaces. It is not intended for aesthetics and any asphalt on top of the aggregate is wasted and tends to reduce the skid resistance of the surface. Fly coating will not fill large cracks and these must be filled using regular crack pouring procedures. Fly coating of shoulders is similar to roadway surface procedures.

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Fly coating is done with CSS-1, SS-1, CSS-1H and SS-1H emulsions diluted with water. These emulsions with no diluents other than water tend to cure more rapidly and track less than emulsions such as EA-300 which contain petroleum diluents or regular cutback asphalts such as the SC types.

The actual asphalt or residual asphalt as it is referred to in the above emulsions varied from a minimum of 57% according to specifications to about 69% as delivered. The dilution rates may vary but normally the rate used is about 50-50. If less residual asphalt is desired, 60% water to 50% emulsion may be the answer.

A normal application rate of about 0.10 gal/yd2 of mixture is applied but each individual route to be fly coated should be evaluated and the application rate adjusted accordingly. Generally there is a tendency to place too much asphalt on the surface which is wasteful and extremely detrimental to traffic. Ponding runoff and long curing time are signs of excessive asphalt.

Generally when temperatures are between 70-90 degrees F. with warm nights and low humidity is the best time to fly coat. It should not be done during early spring or late fall or during extremely hot weather as this also prolongs the curing period.

Consideration must be given for adequate traffic handling during fly coating operations. Adequate signing and flagging must be used until the fly coat has cured. Traffic must be offered detours by the flagman if they so desire.

In some cases, blotting is necessary and encouraged. Blotting fat spots and entrances where stopping, starting and turning movements are likely to occur during the curing period can reduce tracking. Generally, one cubic yard of blotting material will cover a mile. Fine cinders, sand limestone screenings or other fine aggregate may be used.

Fly coating of newly laid leveling courses is not to be done as a routine method to hold the gravel down.

413.9.1 Maintenance Planning Guideline

See Maintenance Planning Guideline for Fly Coating.

Index of all Maintenance Planning Guidelines.

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