 Its purpose is to give the pavement a waterproof and skid resistance service. This presentation was developed for the local technical assistance program, LTAP. It's in three parts, so that after a few minutes of viewing, you can discuss what you've just seen and heard. All three parts are on this tape. Here in part one, we'll look at the preliminary concerns, materials, equipment, surface preparation, weather requirements, and application rates. In part two, we'll look at the chip seal procedures, binder application, chip spreading, and roller operations. Finally, in a third part of the program, we'll look at some of the problems that occurred during chip seal application. Now, because of our country's move to metric measurements, we're going to use metric units throughout this presentation. We'll begin here in part one with preliminary concerns. The first concern is familiarity with the contract documents, your agency's bid specifications, including amendments and any special provisions. The traffic control plan is another important part of the contract documents, especially for chip seal jobs. That's because both the oil and chips compose a real nuisance to motorists passing the work in progress. So most agencies require fresh oil and loose gravel signs on both ends of the work area. That way motorists are warned to use caution when driving over new chip seals. On long jobs, advisory speed signs should also be placed every two kilometers or so. To further protect motorists and the new chip seal, pilot cars may be needed on projects constructed under traffic. So carefully review the traffic control plan, make sure it's approved, and see that it's followed throughout construction. The next step is to check the materials. The first thing you should know is that there are three broad categories of liquid asphalt. Emotions, asphalt cements, and asphalt cements mixed with solvents. Asphalt cements are commonly referred to as ACs, and asphalt cements mixed with solvents are called cutbacks. But all three are typically referred to as binder, or simply oil. Emotions contain both liquid asphalt and water. After application, the water evaporates and leaves only the liquid asphalt on the surface. This is called breaking. You can actually see this happening, the emotion turning from brown to black as the water evaporates. There are two types of emotions, anionic and cationic, with different electrical charges. The type used has to be compatible with the chips used, and this compatibility must be verified in advance. Unlike emotions, asphalt cements and cutbacks don't have water, so their color stays the same. We'll look again at this important difference later. Many agencies require that the binder be provided from an approved source. Some agencies may further request samples, and specify the type of binder to be used. Be sure to follow your agency's requirements. Be sure the chips to be used meet your agency's specs. The size and type of aggregate depends on the number of applications to be made and the type of binder to be used. The aggregate may be gravel, crushed stone, or slag. Individual particles should be cube shaped and as nearly of one size as possible. Graded aggregate should not be used because the smaller material would immerse completely in the binder. It's important for the aggregate to be clean. If it's coated with dust or contains clay or silt, it won't bond properly with the asphalt. Before work begins, make sure that all the chips needed for the job are stockpiled, or that they're readily available. If an emotion is specified, see that the chips are in a surface damp condition. That will keep them from absorbing water from the emotion. Before use, they should be watered down and then allowed to drain, so that they're moist, but not dripping wet when spread. Now let's go over the equipment. On chip seal projects, the first and last piece of equipment on the job is the power broom. Before chip sealing, the surface has to be cleaned to receive the oil application, so dust, sand, stones, and debris need to be swept off as thoroughly as possible. At the end of the job, the broom must sweep off any loose chips without dislodging the chips that are set in place. Damage to the fresh chip seal can result from broom bristles that are in poor condition, or from too much downward pressure by the broom. So see that the bristles are long, like this. Stubby ones would more likely dislodge chips from the surface. And be sure that the broom can float, self-adjust vertically. If it's rigid, they're sure to be too much downward pressure. Now let's consider the distributor. The distributor's function is to apply an even coverage of binder at the proper pressure and rate. Uneven coverage shows up as streaks on the surface. Too much oil in some places, not enough in others. The chips will strip from lean or thin areas. While the oil will bleed in fat or heavy areas, bleeding creates slippery spots on the surface. A safety hazard. To get uniform coverage, first check the spray bar nozzles. They must be unclogged and uniformly angled, usually 15 to 30 degrees in relation to the spray bar. If the nozzles aren't angled properly, the spray fans will hit each other and produce an uneven coverage. It's a good idea to check the spray both before the actual application and soon after start-up, so that any problems can be corrected before the operation moves too far. Spray bar height also affects proper coverage. By adjusting both the bar height and the nozzles, different spray patterns can be made as shown here. Usually a double or triple lap is used for seal coats. The distributor's application pressure is also important to proper coverage. The pressure must be correct and constant. For emulsions, a pressure that is too high, above 206 kilopascals, will cause the emulsion to break on contact with the surface. The proper rate of application is equally important, but we'll look at that later. Now though, let's look at chip spreaders. Three basic types of spreaders place aggregate for chip seals. Two kinds of truck-mounted spreaders and a self-propelled spreader. Whichever kind is used, it must be calibrated and adjusted before the chip sealing begins. Be sure to follow the manufacturer's instructions for correct setup. As with the oil, it's important for the chips to be placed uniformly and at the proper rate. So check the gate controls. And look inside the hopper. The scalping screen should be in good repair so that no large rocks or debris will block the gates. This one obviously needs some work. If the gates and screen do not function properly, you'll end up with either too many chips or not enough. In any case, look over the spreader before the chips are applied and during the application. Stop the operation if you see anything like this. Have the equipment repaired before continuing. Now let's talk about the rollers. Their purpose is to seat the aggregate firmly in the binder. Smooth tread pneumatic-tired rollers are recommended because their flexible tires work the chips into position and embed them in the oil, producing a tight-knit surface. Tire pressures for rubber-tired rollers must comply with the manufacturer's specs. Most important, tire pressure must be uniform from tire to tire. Steel-wheeled rollers may be used to roll chip seals, too. However, the drums sometimes crush the aggregate and bridge over low areas of the surface, so generally they're not recommended. As for the number of rollers, two or more are ideal. Your agency, however, may be limited on equipment, so the actual number will vary. There's one more thing to look for on all the equipment. Leaks. Spot check from time to time to see that there are no oil or fuel leaks. Both would contaminate the new surface. And that's it for the equipment. Now let's look at surface preparation. That surface may be an aggregate base, a previous surface treatment, or a plant mix course. Part of surface preparation is the initial inspection of the road to assess its condition and determine if a seal coat is the proper maintenance treatment to use. Drainage conditions should be part of this initial inspection. See that any problems are corrected before application of the chip seal. Chip seals are not recommended for treating potholes, rutting, bleeding, corrugations, or severe or extensive cracks. Even when such problems are isolated, they must be repaired before chip sealing. Otherwise, they'll just reappear on the new surface. On the other hand, chip seals are effective in treating pavements that are raveling and are oxidized and weathered. In all cases, you need to be sure that the existing surface is completely clean before the chip seal is applied. Hardened mud and other foreign matter may not be removable by brooming alone. Washing or other cleaning methods may be needed. Next, let's look at weather requirements. The temperature is always an important consideration. Most agencies require both the air and pavement temperatures to be at least 15 degrees Celsius and rising. Check your agency's specs for the exact requirements. Keep in mind that this applies to the coolest temperature on the project. If part of the roadway is shaded, check the temperature in the shade. You should also be aware that high wind can greatly affect the binder application, so don't apply the oil if the wind speed is excessive. Of course, nothing causes more problems than moisture. So the operation should not begin at all if rain is likely. Finally, you'll have to determine the application rates for the oil and chips. Many agencies use a table like this that lists the rates for both the liquid asphalt and the aggregate. Notice that a range is given for each rate. That allows you to increase or decrease the coverage depending on the condition of the surface and on the road's average daily traffic. The general rules are, for dried out and porous surfaces, more oil should be applied. For surfaces that are smooth, non-porous, and rich in asphalt, less oil should be applied. In terms of traffic, for lower volumes, a little more oil should be applied. But for higher volumes, a little less oil should be used. As for the chips, the rate applied should leave the surface like this. One layer of chips evenly distributed, with small spaces in between. The rate is expressed as so many kilograms of chips per square meter of surface covered. To determine the application rate for the oil, you first need to know the percentage of residual asphalt content of the liquid asphalt being used. The standard for an emulsion is 63%. Dividing the chip application rate by this percentage gives you the oil application rate in liters per square meter. For further information on determining chip seal application rates, contact your state's Technology Transfer Center. In part two, we'll show you how to check application rates as part of the overall chip seal operation. And with that, we've looked at everything you need to do to get ready for chip sealing.