Section 11: Shooting the AsphaltAnchor: #i1007291
The asphalt distributor is a complex piece of equipment. For a smooth operation, the equipment must be in good working condition and the correct procedures must be followed.Anchor: #i1007301
Heating asphalt binder always constitutes some degree of hazard, with the exception perhaps of emulsions. The most hazardous are cutback asphalts because of the highly volatile solvents used. Extreme care must be taken not to allow open flames to come in contact with the cutback asphalt or the gases from hot cutback asphalt. When working with asphalt cement, the major safety concern is related to the high temperature of the binder. Contact with asphalt cement at 300°F will cause severe burns.
When switching from one type of asphalt binder to another in the same asphalt distributor, thoroughly flush or clean out the previous binder from the system. This will minimize contamination of the new binder and enhance safety of the seal coat operation. When switching from emulsion to AC, the distributor should not be filled to more than half full for the first two or three asphalt shots to minimize foaming and possible overflow via the manhole of the tank. Emulsion in the spray bar is sufficient to cause foaming and tank overflow when the hot asphalt cement is circulated through the spray bar. Switching from cutback asphalt to AC can create a potential explosion hazard, and extreme caution should be exercised.
The distributor must be filled from the heater unit, booster tank, asphalt storage tank, or transporter as shown in Figure 8‑5.
Figure 8-5. Transferring Asphalt from Transporter to Distributor.
When the distributor is full, the number of gallons must be recorded. A strap stick should be used to measure the gallons as described in Section 12.
The asphalt temperature in the distributor must be checked to ensure that it is within the recommended application temperature range. If the temperature is low, the operator should light the burners of the heater unit and start the pump to circulate the asphalt through the pipes. It is also important for the spray bar to be hot. Circulating the asphalt through the system should heat the bar adequately.
The operator should increase the pump speed to make certain the correct pressure is set for the asphalt to be applied. This is important on the first shot of the project, even though the distributor was inspected earlier. It should also be done on the first shot each morning.Anchor: #i1007350
Blow the Nozzles
The distributor should be moved to the side of the road until the correct shooting temperature is reached. When the asphalt has reached the correct temperature and the spray bar is completely off the pavement and in a flat area, one or two layers of joint paper should be placed under the spray bar and the sprayer should be turned on momentarily to “blow out” the nozzles. While spraying, each nozzle should be visually checked to make certain no nozzles are clogged and the spray pattern looks correct.
If any nozzles are clogged, they should be removed and cleaned out with an appropriate solvent. After cleaning any nozzles as needed, the nozzles should be blown out, and the spray pattern should be checked again. The spray system should be checked for leaking asphalt. If no leaks are apparent and all nozzles are working correctly, the distributor may be moved into position at the beginning of the asphalt shot.Anchor: #i1007365
Check Spray Bar Height
To check the spray bar height before applying the asphalt, refer to Chapter 7 Section 3. The distributor should stand by in a ready position while other final equipment checks are made.Anchor: #i1007377
Final Equipment Check
A final check must be made to ensure that all the other equipment is in position and ready before allowing any asphalt to be sprayed. The aggregate spreader box should be in position and ready to begin. The required number of haul trucks needed to cover the asphalt shot must be in position behind the spreader box. If a patching crew will be used on the job, they should be ready to follow the haul trucks as closely as possible. All the rollers should be ready to begin.Anchor: #i1007387
Paper Joint Check
The paper joint should be in place for the beginning and the end of the asphalt shot. It should be of adequate width for the type of distributor being used and the skill of the operator. The distributor spray bar should be positioned over or behind the paper joint for the beginning of the asphalt shot. This will enable the spray bar nozzles to be opened on the paper joint at the beginning of the asphalt shot. Figure 8‑1 shows the correct position for the distributor.
Figure 8-6. Correct Starting Position over Paper Joint.Anchor: #i1007407
When the distributor is in position over the paper, the transverse alignment should be visually checked. The end nozzle should be directly over the line, which the operator will use as a guide. As soon as the transverse alignment is correct, the operator should set the guide bar so that alignment is in position over the reference line.Anchor: #i1007417
Applying the Asphalt
As soon as all the preceding checks have been made, including strapping the distributor, the application of asphalt may begin. The inspector should be in position to closely observe the early part of each shot to see that the fan pattern is correct and all nozzles are spraying properly. The asphalt applied on the roadway surface should be closely inspected to detect any variation. It should appear as a uniform sheet of asphalt across the entire width of the shot. If any streaking, ridging, puddling, or flowing of asphalt off the roadway surface is observed, the operation should be stopped immediately and corrections made.
After completion of the asphalt shot, the distributor should be strapped as described in Section 12.Anchor: #i1007434
Timing for Aggregate Application
For best results, aggregate should be applied on any type of asphalt binder as soon as possible without causing the rocks to turn over or the asphalt to be picked up on spreader box, haul truck, or roller tires. That is, the aggregate spreader should follow closely behind the asphalt distributor. Refer to Section 14 for more information on spreading the aggregate.Anchor: #i1007444
If additional distributors are used, make certain that the same checks are performed on all distributors. If the distributors are identical they should be numbered so that they can be easily distinguished.