413.8 Spot Seal Coating
Spot seal coating consists of sealing lean, oxidized, or map cracked areas small in size. If spot sealing cannot be controlled to a maximum of 10 percent per mile of the roadway surface on each mile at any one time, other means of repair should be considered.
Spot sealing is considered preventive maintenance and should be done before the oxidized or cracked areas deteriorate further. It should be done during hot weather, preferably the summer and early fall months, from May 15 to September 15.
CRS-2 emulsified asphalt is normally used. The asphalt is applied with a hand spray or distributor dependent on the actual and contemplated size of failure. Experience determined which method is the most economical and practical. Normally the hand spray method is only practical when the failures are small spot failures and not progressive. The asphalt is applied at an average rate of .35 gal/yd2, but control is difficult and the amount should be just sufficient to embed the aggregate enough to hold. Excessive asphalt will cause subsequent bleeding especially if the work is being done in cold weather.
The placement of cover aggregate should immediately follow the application of asphalt and be spread at the rate of 25 to 30 lb/yd2. On all work, the amount should be controlled closely to prevent waste. It may be spread by hand, tailgating from a truck, or by a mechanical spreader. All areas shall be rolled immediately with a steel drum roller. Where the template of the road is poor rolling should also be done with a loaded truck. Rolling should be continued until the aggregate is firmly embedded. Cover aggregate should not exceed 1/2 in. maximum size for warm weather, and 1/4 in. maximum for cooler weather, unless the treated areas is such that larger aggregate can be embedded firmly to provide for more stability. On higher type surfaces, the aggregate must meet specifications for seal coat aggregate. Crushed creek gravel may be used only if no other cover aggregate is available. If used, a minimum amount should be applied and additional rolling performed to embed such aggregate firmly. Brooming should be kept to an absolute minimum and any brooming done should be done lightly.
If the areas sealed lose their cover aggregate, additional aggregate should be applied and the areas rolled well. If the aggregate will not embed, sharp, clean sand should be applied and rolled wall to check the bleeding.
Proper traffic control, flagging and signing must be used on spot sealing operations to assure the safety of the public and our crews, and to minimize the whipping off of aggregate by traffic.
