Tips for Chip and Seal Application with Emulsions
Emulsion chip seal suggestions:
- Material should meet the specification supplied.
- Temperature in the distributor should be maintained between approximately 150 – 180 degrees F.
- At start-up, the grinder should be circulated in the distributor bar until the bar temperature is 140 – 180 degrees F. Initially this will take 2 – 5 minutes; after start-up, this step is not needed.
- Make sure that the emulsion has not been chilled during shipment. This is particularly important in regions where the shipment might be transported over high mountain passes. Chilling and / or freezing may lead to product separation.
- Check the weather forecast. Make sure there is no forecasted rain for at least 4 hours before and after the brooming operation.
- The bar should be made parallel to the pavement at 10 inches (+/- 1 inch) above the pavement.
- Nozzles for the Bear Cat distributor should be #2s. For other distributors, the manufacturers should be consulted. Case should be taken to ensure that proper pressure can be applied. If the nozzle is too small, high pressure could result in over-spray and “bouncing” of the asphalt. Too large a nozzle results in an improper fan or roping. Both of these conditions should be avoided.
- The nozzles should be angled at 35 degrees from the bar. The end nozzles should be at least 90 degrees to help ensure a sharp edge.
- A test shot should be made at a pit to determine if the above conditions are being met.
- If smooth lay down does not occur due to cold pavement temperature, the distributor temperature should be raised; be careful to maintain the temperature between 150 - 180 degrees F. Do not exceed 180 degrees F.
- The aggregate should be uniform and slightly moist. The moisture content should be approximately 2 – 3.5 percent by weight (a handful of rock should feel damp in your hand). If the moisture is too low, bonding will be difficult. Usually, wetting down the pile lightly will help overcome the problem.
- Pneumatic rollers should be used for rolling. They conform well to variations in the pavement and do not crush the aggregate.
- Rollers should travel at 5 – 7 miles per hour. Higher speeds result in thrown rock and rollover of the aggregate. Rollover can cause tracking.
- Binder application rate is dependent upon the type and size over the aggregate. Guidelines are:
½” blocky material requires 0.35 to 0.45 gallon / yard2
½” flaky material requires 0.30 to 0.40 gallon / yard2
3/8” blocky material requires 0.25 to 0.30 gallon / yard2
3/8” flaky material requires 0.20 to 0.25 gallon / yard2
- Binder application rate is also strongly influenced by the type of base pavement and its condition. The rates listed above are for dense graded hot mix asphalt in good condition (no raveling). Rates should be increased for open graded friction courses or chip seals by 0.05 to 0.1 gall / yard2, depending on how dense or smooth the surface has become.
- Like the binder application rate, aggregate spread rate is dependent upon the blockiness, density, and grading of the rock. However, a general rule is:
½” should use 25 to 30 pounds / yard2
3/8” should use 22 to 27 pounds / yard2
- The spread rate and uniformity of the spreader should be checked by looking through the veil as the rock is falling. The tires of the spreader shuld be partially visible. The veil should be uniform across the entire trough.
- Self-propelled brooms are preferred because they have the weight and the force needed to dislodge nested rock. It is essential that the nested rock be brooned off the pavement. This is rock that can break windshields.
- Normally, three brooms are required. Brooms should be staggered with a 50% overlap (width) such that rocks are moved from the center line to the shoulder. Start at the center line and broom to the shoulder.
- Brooming should not start until the emulsion has broken and set. This usually requires 30 to 45 minutes after the aggregate has been spread and rolled. Pulling a rock up by hand will allow you to judge this. A good bond should have developed between the asphalt and the aggregate. This could take as long as several hours under adverse conditions, such as cool, damp days, or at very high temperatures where skinning may occur.
- Traffic should be controlled for at least 24 hours to ensure complete setting to the binder, and proper bonding of the aggregate.
- A thorough brooming after 24 hours is very helpful. Some rock may have become dislodged. The surface should be inspected and checked by the resident engineer before brooming. It has been our general experience that final striping can follow this brooming.