 The North Carolina Institute for Transportation Research and Education presents pavement structure repair techniques, asphalt chip seals. A seven-step procedure will be presented for performing asphalt chip seal operations. By following this procedure, an effective asphalt chip seal can be installed. The asphalt chip seal procedure consists of, 1. Examine existing pavement, 2. Repair pavement, 3. Clean surface, 4. Apply asphalt, 5. Spread aggregate, 6. Roll aggregate, 7. Remove excess aggregate. Do not begin repair procedures until proper traffic control measures are in place. Proper traffic control provides a safe work site for the work crew and provides safe passage for the traveling public. Consult the MUTCD and other appropriate work zone traffic control standards and guidelines to determine the traffic control requirements for the particular maintenance activity. For more information, refer to the videotape Basic Traffic Control for Pavement Structure Repair Techniques. The purpose of an asphalt chip seal is to provide a waterproof layer and a skid-resistant surface. A chip seal can be applied to an aggregate base, a previous surface treatment, or a plant mix surface. Asphalt chip seals can be single or multiple layers. A single layer asphalt chip seal consists of a sprayed application of asphalt covered with a layer of aggregate of a uniform size. A multiple surface treatment consists of repeating the process with the aggregate size becoming smaller with each application. Seals are an effective maintenance activity when used to repair the proper conditions but are subject to rapid failure if used to repair the wrong conditions. Asphalt chip seals are not designed to bridge weak spots or to mask underlying pavement deficiencies. The following pieces of equipment are needed for application of asphalt chip seals. One, asphalt distributor. Two, aggregate spreader. Three, one or more rollers, preferably a rubber-tired roller. Four, power broom. Five, dump trucks. The first step in the seven-step procedure is to examine the existing pavement. This examination is done to determine whether a seal would be a suitable maintenance activity for the pavement distresses present. Seals are not effective on extensive structural failures, such as severe cracking and rutting, but are effective in treating the following distress conditions. Ravelling. Ravelling is a loss of aggregate from the surface layer of the pavement. It can be caused by the hardening of the liquid asphalt, poor application techniques, or an insufficient quantity of residual asphalt. This condition is most common on existing asphalt chip seals that are several years old. Oxidized and weathered pavement surfaces. Pavement surfaces become oxidized and weathered with age. As pavements age, the asphalt in the surface is oxidized, resulting in a brittle condition and loss of aggregate. The surface aggregate may also become worn and polished over time due to traffic wear and weathering. Light alligator cracks are longitudinal cracks about one-eighth inch in width and usually occur in the wheel paths. These longitudinal hairline cracks are an indication of structural damage to a pavement. Frequently, pavements with only hairline alligator cracks do not have rutting associated with the cracks. These pavement distresses represent conditions for which asphalt chip seals are an effective maintenance technique. Review drainage during the pavement examination. Many pavement distresses result from poor drainage. Look at the condition of ditches and other drainage areas to make sure they are open and at a level below the bottom of the sub-base. The need for patching, leveling, or drainage repairs prior to a seal is evaluated during the existing pavement examination. Step two is pavement repairs. It is absolutely essential to repair the existing surface before the seal is applied. Typical repairs prior to an asphalt chip seal include pothole patching, full-depth patching of badly broken alligator pavement, and leveling of areas with rutting and depressions. Correct drainage deficiencies prior to the seal work. Drainage corrections might include cleaning out blocked ditches or making ditches deeper. Once the repairs are made, the pavement is ready to be sealed. The third step in the asphalt chip seal procedure is clean the surface. Clean the surface prior to spraying asphalt. Cleaning is usually performed with a tractor mounted power broom. This is effective for removing loose sand, stones, and debris. Remove hardened mud and other foreign matter before the seal is installed. The objective is to provide a clean pavement surface for the asphalt to bond with. The fourth step in this procedure is the application of liquid asphalt. The asphalt application is the most important part of a chip seal operation. Emulsified asphalt is recommended. However, cutbacks and asphalt cements can be used with good results. Select an emulsified asphalt based upon the compatibility of the emulsion and the aggregate. There are two basic types of asphalt emulsions, cationics and anionics. The cationic emulsions have a positive charge while the anionic emulsions have a negative charge. The charge of the aggregate and the emulsion should be opposite. Like charges repel while opposite charges attract. One advantage of using asphalt emulsions is their ability to coat damp aggregates. The emulsion contains approximately one-third water, which will be lost by evaporation. Apply the liquid asphalt using an asphalt distributor. The distributor consists of a truck-mounted or trailer-mounted insulated tank with appropriate controls for setting the rate of asphalt application. The tank contains a heating system to maintain the asphalt at the required application temperature. At the back of the tank is a system of spray bars and nozzles through which the asphalt is forced under pressure onto the pavement surface. The distributor tank should be equipped with a circulating system to prevent asphalt from solidifying in the spray bars. The width of application is varied by cutting off portions of the spray bar. Follow the manufacturer's instructions for specific distributors for adjusting spray bar height and nozzle settings so that the desired application rate and coverage is achieved. The distributor uniformly applies asphalt to a surface at a specified rate regardless of changes in grade or direction of movement. A hand spray attachment is convenient for applying asphalt in areas that are hard to reach with the spray bar. Asphalt application rates are determined by several factors including the size and type of aggregate and the type and grade of asphalt and the condition of the pavement. Be certain to check the asphalt application rate. Too much asphalt causes bleeding. Too little causes a loss of aggregate chips. To check the asphalt application rate place a one-square-yard pan in the path of the distributor then measure the amount of asphalt collected. Proper weather conditions are extremely important for an effective chip seal. Hot and dry weather is ideal for performing seal work. Do not schedule work if the air temperature is below 50 degrees or if the pavement temperature is below 70 degrees. Once the distributor has been adjusted to provide the proper asphalt temperature and the selected asphalt application rate the liquid asphalt is ready to be sprayed. Position the asphalt distributor at the starting point to apply the emulsified asphalt. In order to provide a straight edge at the beginning and end of the shot place building paper across the lane just ahead of the beginning point and just past the endpoint. Then the distributor traveling at the correct speed for the desired application rate starts spraying on the building paper so that when it reaches the exposed surface the application rate is uniform. The most common problem associated with improper asphalt distribution is streaking. Streaking is caused by one or a combination of the following conditions. Clogged distributor nozzles, improper pump pressure, interference from adjacent nozzles or improper spray bar height. Monitor each of these conditions during the spraying operation and make adjustments as needed. The fifth step in the asphalt chip seal procedure is the spreading of aggregate. Spread the aggregate immediately after the distributor sprays the asphalt. The aggregate should be placed before the emotion breaks. Emulsion is chocolate brown when put down but turns black when the emotion breaks. The water is released into the air leaving only the asphalt. The size and type of aggregate used depends on several factors including the number of layers being installed and the type of emotion being used. Aggregate used for chip seals should be cubicle in shape and is near to a one size material as is economically feasible. Do not use a graded aggregate as the smaller sizes may become immersed in the asphalt film. It is important that the aggregate be clean. If the aggregate contains a film of dust, clay or silt this may prevent a good bond from forming with the asphalt. It is also important that all the aggregate needed for a particular project be on hand or readily available before starting the operation. The number of dump trucks needed to haul aggregate depends on the haul distance from the aggregate to the work site and the productivity rate of the spreader. There are three basic types of aggregate spreaders. Tailgate spreaders attached to the tailgate of the truck. Truck mounted spreaders which are attached to the tailgate of the truck and the truck propels the spreader by backing. Mechanical self-propelled spreaders which actually pull the truck. The mechanical self-propelled spreaders provide the most uniform and continuous distribution of aggregate but are the most expensive. Regardless of the type of spreader being used it is calibrated and adjusted prior to beginning the chip seal operation. Aggregate application rates like asphalt application rates can be calculated using a formula or taken from tables. Make a quick check on the amount of aggregate being applied by laying a one square yard section of cloth on the ground and passing over it with the spreader. Then carefully lift the cloth and the aggregate and weigh them. This will give the application rate of the aggregate being spread. The aggregate spreader also begins and ends spreading aggregate on the building paper just as the asphalt distributor. Once the aggregate is spread the paper is removed leaving a straight and neat joint. Following the aggregate spreader, step number six is the rolling operation. The rolling operation proceeds immediately behind the aggregate spreader. A self-propelled smooth tread pneumatic tire roller with a tire pressure of 60 to 90 pounds per square inch is recommended. The pneumatic roller's tires force the aggregate firmly into the asphalt binder. Steel wheeled rollers have been used successfully for compacting chip seals and can be used if a pneumatic roller is not available. Steel wheeled rollers are not generally recommended because they can crush aggregate and bridge over low spots in the pavement. Begin rolling at the outer edge of the seal and proceed in a longitudinal direction working toward the center of the road. Each pass overlaps the previous pass by about one half the width of the front wheels. Rolling continues until the surface is smooth and compacted. If multiple seals are being installed apply the second shot of asphalt followed by a second layer of aggregate. For multiple seals adjust the asphalt and aggregate application rates for each application. Broom the surface lightly to remove any excess aggregate. This is the seventh step in the chip seal procedure. If necessary this is done after a good bond has been formed between the asphalt and the aggregate. The term lightly is emphasized because excess pressure with a broom could loosen the aggregate. In rural areas broom the aggregate to the shoulder of the roadway. In urban areas broom the aggregate to the curb or center of the street and remove manually or with a vacuum device. The newly sealed road is ready to be open to traffic. Placement of loose gravel signs and reduced speed signs is recommended. These should be left in place for at least 24 hours. Let's briefly review the seven step procedure for installing an asphalt chip seal. Step one, examine the existing pavement. Examine the pavement for surface distresses and drainage problems. Step two, repair the pavement. Complete pavement and drainage repairs prior to the installation of a chip seal. If these distresses are not repaired prior to the seal placement they may reappear soon afterward. Step three, clean the surface. Remove all loose material from the pavement surface prior to the seal application. A tractor mounted broom is effective in removing most loose debris from the pavement surface. Step four, asphalt application. The asphalt application is the most important part of a chip seal operation. Emulsified asphalt is recommended. The asphalt distributor is set up for the proper application rate. Monitor the application for proper application rate to prevent streaking. Step five, spread aggregate. Spread the aggregate immediately after the asphalt is sprayed. When using emulsified asphalt, spread the aggregate before the emulsion breaks. Aggregate must be clean so that a good bond can form between it and the asphalt. Step six, roll the aggregate. Roll the aggregate immediately after the aggregate is spread. A pneumatic-tired roller is recommended to roll the aggregate. A steel wheel roller may crush aggregate or bridge over low areas. Step seven, remove excess aggregate. If necessary, remove excess aggregate by lightly brooming the surface. Placement of reduced speed and loose gravel signs is recommended when the road is open to traffic. By following these seven steps, an effective asphalt chip seal can be installed and provide a better road for the traveling public.