Apply tack cautiously By John S. Ball III
A distributor truck operator who puts safety first is an asset to the paving crew
The sun is just coming up over the horizon and the music of chirping birds greets you as you step out of your truck at the job site. Other crew members are arriving now as well, but theres one person whos been here for a while already. The first person to arrive at the job site is generally your distributor truck operator. Hes not just earning brownie points with the supervisor by getting to the job site ahead of everyone else. Hes there early for some important reasons.
The first reason the distributor truck operator arrives early is to get the distributor in operational condition. He or she knows that the day starts with heating the liquid in the distributor tank to a certain degree, and that takes some time.
The operator also arrives early to map out the days gameplan. If he or she gets a jump start on the day, the distributor can be warming up while the operator talks to the supervisor about the days paving project. When the person applying the tack knows when and where he or she will be needed, it makes the rest of the day go a little more smoothly.
That early start and the distributor truck operators commitment to his or her job will make a difference in how safely and efficiently your crew paves the rest of the day. His or her actions will not only affect the paving schedule, they will affect the safety of every crew member. Here are some tips to help the distributor truck operator perform his or her job better and keep everyone at the site a little safer.
Take startup one step at a time
Getting the distributor in operational condition involves heating the liquid inside the tank. The operator is in charge of heating up the baffles, heating up the liquid and staying close to the truck every second. If the fire goes out or the fire gets carried away, it can burn the distributor truck up in 10 minutes or less. So the operator needs to maintain a good position around the vehicle so he or she can make sure the flame doesnt get out of control.
While things are heating up, the operator should check the hoses and fittings. He or she needs to check the joints where the bars come down to make sure the tacking isnt loose or leaking. Even though the distributor truck is messy by nature, you dont want it to be dripping liquid from any orifice. You want it to be a tight unit. As part of checking out the machine, the operator should do a full walk around the vehicle to make sure all the packing is good and that the tips are all clean.
The operator is also circulating the liquid in the tank while things are heating up. If the material stays stagnant, the temperature will not stay even throughout. Most distributors have a circulating button on the control panel that the operator can push and the machine will draw the liquid down through the bars, circulating everything around so it stays evenly heated.
Spray with caution: truck application
Remember the gameplan the supervisor and distributor truck driver discuss at the beginning of the day? That plan determines how the operator will spray the liquid. You want to spray tack in the same pattern that your crew will pave. If youre going to pull a 25-foot (7.6-m) pass in a northbound direction with the paver, then reset at the south end to pull the second 25-foot (7.6-m) pass in a northbound direction, you want to spray the tack in the same manner. If the distributor truck operator knows what the paving pattern will be ahead of time, he or she can get the tack down in time for it to break before the paving crew has to get on it with the new hot mix asphalt (HMA).
Knowing the paving pattern is the distributor truck operators best tool for keeping the paving crew on schedule, but the operator has several conditions to consider before he or she begins spraying. The first of these conditions is the wind. Wind direction and speed will determine how high off the ground the distributors spray bar can be. Wind direction and speed also determine when the spray can begin. If a parking lot full of bright, shiny cars sits a mere 6 feet (1.8 m) from your paving site, a 30-mile (48-km) per hour wind will take the spray straight to the sides of those cars. It doesnt take a seasoned veteran to tell you that detailing a lot full of cars will cut into your profit on the project. If the wind is blowing steadily all day, the foreman on the project will have to decide whether the spray can be contained to the project site by lowering the spray bar, or if the project can be postponed to another day. The typical spray bar height will be 12 to 15 inches (300 to 375 mm) off the ground. The higher you have the bar, the more chances youre going to have of spraying tack all over the place. By lowering the bar, you allow a better overlap of spray between the nozzles, thus getting optimum tack coverage on the ground (See Figure 1, above).
Besides height, another aspect of the spray bar to pay attention to is the nozzles. Depending on the spray bar, there can be a dozen or more nozzles with varying types of orifices for releasing liquid tack. The nozzle spacing and orifice type you choose depends on the type of liquid youre spraying and how thick you want to spray it. Different orifices will provide different spray patterns, so choosing one that best fits your project takes some research.
Once the operator has checked wind direction and speed, and adjusted the spray bar according to the liquid being used and the wind direction, he or she must determine the travel speed for the distributor truck. For some projects, this speed may already be determined easily by inputting information into a control panel in the cab of the truck, then letting the machine set the speed itself. But not every operator has the luxury of a recent model truck with an on-board computer. Some drivers will still need to calculate travel speed in order to get the spray rate just right.
When all the calculations have been made, the truck driver has the physical job to perform. Backing up the truck to start spraying the first pass seems like a simple thing to do, but the driver has much to stay aware of at this time. He or she must make sure the path is clear. He or she must make sure the spray bar is high enough off the ground during travel to avoid any bumps or surface irregularities. He or she must make sure the spray bar is not extended to the point it will hit nearby objects as the truck is backing into position. Once in position, the operator can adjust the spray bar into the predetermined position, extend it, if necessary, and begin the application of tack.
Spray with caution: hand application
When the crew finds the area to be tacked is too tight for the distributor truck to back into, application of tack is usually done by hand wand. This, too, is not as easy as it sounds.
There is a spray wand on the side of the truck, and that is where the easy part ends. One thing the operator wants to be sure of, before he or she picks up the spray wand, is that it is in the off position. He or she should also make sure the wand is in good working order. Check for cracks, and make sure the fittings are tight, not leaking. Also, before the operator picks up the wand, make sure he or she is wearing protective clothing, such as a coverall suit, thermostatic gloves, eye protection, a hat and good work shoes. The material that comes out of the wand will be scalding, so it is best to be prepared just in case something splashes onto the operator. You want to be cautious.
Before turning on the wand, the operator must have it pointed toward, and low to, the ground. Again, wind direction and speed is going to play a role in how tack is applied by wand.
Crews typically use the wand on the transverse joint, which is the beginning of paving. The person applying tack with the wand wants to be sure to tack along the face of the joint. Usually the person sprays out 5 to 10 feet (1.5 to 3 m) by wand, enough so the distributor truck operator can get backed in.
When its time to back the truck to the starting point, the operator must take care of the wand and hose he or she has been using. Ive seen many a hose ripped off as the distributor truck driver runs over his own hose. Take the time to shut off the hose properly and wrap it up when you put the wand back on the truck and you will save expense as well as a safety problem.
Paving crews are usually in a hurry to get the tack down, but a responsible tack applicator will take the moment to take care of safety. If the hose drags on the ground as the truck is moving, weak spots and tears develop. Imagine picking the hose up off the ground, turning the spigot to start the flow of 400° F (204° C) tack and having the hose explode behind you. If the hose develops a hole, hot liquid will shower everywhere, getting on the operator and anyone else close to the truck. This can be avoided by taking proper care of the hoses.
Dont let other safety issues arise because the crew is in a hurry. When tacking a longitudinal joint, it is proper to spray down the length of the joint by walking along the joint with the spray wand. The truck driver can pull the truck forward at certain intervals. It is not proper to try to spray tack from the wand while the truck pulls forward. Crews may be tempted to let the wand operator hang from the back of the distributor truck while the truck drives at 10 to 20 miles (16 to 32 km) per hour down the lane. This is an unsafe practice. At those speeds, hitting a bump or a dip in the road will not only cause the spray wand to jump in the operators hand, sending spray all over passing traffic, it can cause the wand operator to fall off the back. The goal of the tacking operation is an even distribution of tack, so having someone perform the application while hanging off the back of the truck is not only a safety risk, it is also inefficient. Take time to do the job correctly and safely.
Oil and water still dont mix
Safety measures during application of any kind are important, but distributor truck operators have an additional area of safety to stay aware of. The operator/driver should always know what material is in his or her tank. When it comes time to refill and the driver pulls up to the tank farm, the attendant will ask what material has been in the tank .
If the tank has a water-based emulsion in it and youre requesting a liquid asphalt mix, which is all petroleum product, youre asking for trouble. The steam evaporates quickly in the tank as the oil product is introduced. As the steam condenses, it will expand, and it will come up like foam, blowing a hole in the tank from here to Kingdom Come.
Clean up after yourself
When the distributor truck operator gets to the end of the day, cleaning the equipment is paramount for him or her. Leaving some tack to cool overnight at the spray bars nozzles is asking for a problem tomorrow. Different manufacturers of distributor trucks will have different devices to help the operator clean out the system. Some offer a reverse suction system that literally pulls material from the spray bars back up into the tank. This system employs an asphalt pump, which the operator can activate from inside the cab. For more thorough cleaning, operators can use a solvent with a flushing system. Some manufacturers offer self-flushing systems that circulate solvent from a tank throughout the system, flushing the pumps and piping as well, then store the material in a tank for reuse or disposal.
Throughout the day, the distributor truck operator uses a release agent to keep the spray bar nozzles clear and unplugged. At the end of the day, he or she has to ensure the entire spray bar system is unplugged before leaving the machine.
Safe practices should never take a break
Keeping the crew safe is only one aspect of safety. Distributor truck operators and paving foremen also have the general public to worry about. Whether a motorist is driving alongside the paving site or trying to reach a business on the other side of your paving site, it is the crews responsibility to keep that motorist safe. It is important to keep the motoring public from getting between the distributor truck and the paver. Although it may seem obvious to crew members that a paver will follow a distributor truck, the average driver probably doesnt see it as so obvious. The more cones you have set up alongside your site, the better your chances of keeping drivers from entering the work zone. Once a car has driven across the freshly sprayed tack, you have a mess, so its best to make it obvious to motorists where your site begins and where it ends. Unless you know midnight tack will be this years hottest color coming out of Detroit, apply tack safely, responsibly and exactly where you want it.
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