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23 Bar Set Too High Bar Set Too Low Streaks from Excess Emulsion Streaks from Lack of Emulsion Figure 5. Streaks caused by incorrect bar adjustment (after Wood et al. 2006). 2. Calculate spray rate = 1,580 gal/(12 ft 4,630 ft/9 ft2/yd2) 3. For truck no. 3: = 0.26 gal/yd2 a. Load = 23,848 lbs a. 0.32 - 0.26 = 0.06 gal/yd2, which is greater than 5% b. Spreader distance = 213 ft of the difference between the actual spray rate and c. Rate = 23,848/213 12/3 = 28.0 lbs/yd2 the design. 4. Average rate = (27.9 + 28.3 + 28.0)/3 = 28.1 lbs/yd2 3. Therefore, make adjustments to distributor speed or 5. No adjustment needed (measured rate is within 1% of spray bar until the rate applied is within 5% of 0.32. design). 7.1.2 Chip Spreader Compensation for moisture on chips must be taken into account when calibrating chip spreaders. The chip spreader should be checked for uniform applica- tion both laterally and transversely. Lateral distribution is best checked using ASTM D 5624, "Standard Test Method 7.2 Operations for Determining the Transverse-Aggregate Spread Rate for 7.2.1 Pavement Preparation Surface Treatment Applications." Once accomplished and any spreader gates have been adjusted for variations, the lon- The substrate pavement should be structurally sound before gitudinal spread rate can be measured by applying the entire chip sealing. Areas exhibiting alligator cracking should be spreader capacity to the pavement and measuring the appli- patched the full depth of the pavement section using hot mix cation rate. The mass of chips applied can be determined from asphalt. The surface of these areas should be sprayed with a weigh tickets of trucks loading the chip spreader. Conduct the light application of slow-setting asphalt emulsion diluted calibration for three trucks and average the results. An exam- 50:50 with water at the rate of 0.10 gallons per square yard ple follows. and allowed to cure thoroughly before chip sealing so that the For 12-ton capacity tandem dump trucks, 12-ft-wide pave- new chip-seal binder will not be absorbed into the surface of ment, and 28 lbs/yd2 design spread rate: the new patch. Failure to do this could lead to loss of chips under traffic. 1. For truck no. 1: The substrate pavement should be clean before commenc- a. Load = 23,803 lbs ing chip-seal operations. Dust and debris on the surface should b. Spreader distance = 213 ft be removed by power brooms. Pickup type brooms should be c. Rate = 23,803/213 12/3 = 27.9 lbs/yd2 used in urban areas to avoid spreading surface contaminants 2. For truck no. 2: onto adjacent properties. Push brooms may be used in rural a. Load = 23,921 lbs areas when spreading excess chips onto shoulders does not b. Spreader distance = 211 ft affect property owners. The surface of the substrate pavement c. Rate = 23,921/211 12/3 = 28.3 lbs/yd2 should be damp to dry. A damp surface is acceptable as long as Turn Off These Nozzles Turn Off These Nozzles Emulsion Contact for Double Lap Application Emulsion Contact for Triple Lap Application Figure 6. Obtaining no streaking for double and triple lap application.

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24 moisture is present only in surface aggregate voids and is not spraying. If the chips are applied too early, there is risk that the present as free moisture between aggregates. chips will roll over in the emulsion due to momentum created by the forward movement of the chip spreader. Thus, less binder will be available to hold the chips in place and the 7.2.2 Environmental Conditions exposed binder becomes susceptible to being picked up on The pavement temperature for chip-seal operations should roller tires. Therefore, the adhesive quality of the emulsion be a minimum of 70F with little or no wind. However, chip- should be checked to determine when to apply the chips. This seal operations may commence before the pavement tem- may be determined by throwing a handful of chips onto the perature reaches 70F as long as pavement temperatures are emulsion and observing whether they stick to the surface or expected to be 70F and rising within 60 minutes after com- tend to roll over. Some experimentation is necessary to es- mencing work. timate the proper timing, which can be accomplished dur- Wind speeds in excess of 20 mph transverse to the pavement ing the first distributor application. In many cases, changes alignment can blow asphalt emulsion onto opposing traffic in environmental conditions during construction will require on two-lane facilities; therefore, chip-seal operations should this test be repeated during the day because humidity, chip be avoided under these conditions. moisture, emulsion properties, and ambient air temperature Chip-seal operations should not be pursued if rain is affect the adhesive quality of the emulsion. threatening. A rain storm could wash asphalt emulsion onto concrete gutters or into roadside ditches. 7.2.5 Rolling Ambient air temperatures in excess of 110F with the sun shining or with moderate winds can cause emulsified as- Different types of rollers have been used to embed chips on phalts to form a skin on the surface such that the emulsion chip seals. Pneumatic rollers have a tendency to pick up chips does not set adequately. This situation may require the due to the affinity of asphalt residues for rubber tires. How- spread of chips closer to the distributor to obtain proper ever, these rollers do not crush chips in situ as do steel- embedment. However, high air temperatures may lead to wheeled rollers. Although lightweight steel rollers of three tons lower viscosity emulsion residue, resulting in higher poten- or less may provide a means of leveling the surface of a new tial for pickup on rubber tire rollers. Increasing the demul- chip seal after pneumatic rolling, caution must be applied to sibility of anionic emulsions may help remedy this situation avoid breaking aggregate chips. Steel rollers with rubber- (Shuler 1991). coated drums are also a good tool for embedding chips. How- There is anecdotal evidence to support limiting the season ever, any rigid drum roller will bridge over areas of the pave- for chip sealing so chip seal construction does not occur ment with permanent deformation, causing these areas to be when there may be periods of cool to cold weather. inadequately rolled. Rollers must be able to keep up with the distributor and chip spreader and provide enough passes to embed the chips. 7.2.3 Emulsion Application If the rollers travel too fast, embedment will not be achieved. Each emulsion application should start and stop by spray- Therefore, the number of rollers used depends on roller speed, ing on top of 15 lb/yd2 roofing paper or similar dimensioned, roller width, distributor and chip spreader speed, and the equally heavy craft paper placed transverse to the centerline of number of passes required to achieve embedment. The faster the pavement. This creates a neat, sharp transverse joint. The the rollers move, the more rollers will be required to achieve distributor operator should position the spray bar at the rear embedment. This is because rollers need to linger over an area of the paper on takeoff so that by the time the bar reaches the of chip seal to obtain the desired chip embedment (Benson pavement the distributor speed is appropriate for the desired and Gallaway 1953, Elmore et al. 1995). The number of rollers spray rate. Another sheet of roofing paper should be placed required can be calculated based on this linger time and the across the pavement before the distributor stops. Spraying assumption that the rollers should match the production should stop when the spray bar has passed over the paper. Cal- of the distributor and chip spreader as follows (Gransberg culating when approximately 90% of the distributor volume et al. 2004): has been sprayed is a good method to determine the distance where the second strip of roofing paper should be placed. N = 6.67 Px A Where 7.2.4 Chip Application N = number of rollers; Chips should be applied to the surface of the fresh emulsion P = distributor speed, fpm; before it begins to set but not necessarily immediately after x = lane width, ft; and

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25 A = area covered in one hour by rollers to get minimum tles should be applied with much care to avoid damage to "linger," yd2. the fresh seal. As an example, for a distributor traveling at 200 fpm and spraying 12-ft wide at a conservative 5000 square yards per 7.2.7 Vehicular Traffic Under Traffic Control hour coverage rate, N = 3.20 (i.e., use 4 rollers). Fewer rollers will not be able to keep up with the distributor and spreader Vehicular traffic may be allowed on the fresh seal after ini- while maintaining the 5000 yd2/hr rolling rate. If they do keep tial sweeping if speeds can be controlled to less than 20 mph up, the rollers will not spend enough time embedding aggre- using pilot vehicles. If speeds cannot be controlled to this gates because they are traveling too fast. speed, vehicles should not be allowed on the seal until final sweeping has been completed. Traffic control using pilot ve- hicles should be applied following the Manual on Uniform 7.2.6 Initial Sweeping After Rolling Traffic Control Devices for Streets and Highways (2009). Light brooming should occur as soon as possible after rolling and before vehicular traffic is allowed on the surface to 7.2.8 Removing Traffic Control remove any excess chips. This should be possible when the moisture content of the chip seal reaches the level where 10% Traffic control may be removed and vehicular traffic allowed chip loss occurs after the laboratory sweep test. This moisture on the fresh chip seal after brooming has been completed content, measured by the moisture loss test, was found to be to remove excess or loose chips and the moisture content approximately 15% to 25% of the total moisture present in the of the seal reaches the level that results in less than 10% chip chip seal and indicated that total moisture consists of water in loss after the laboratory sweep test. This moisture content, the emulsion plus moisture in the aggregate chips, but not measured by the moisture loss test, is approximately 15% moisture in the pavement (see attachment). Moisture content to 25% of the total moisture present in the chip seal (which of the chip seal should be measured in areas of the project consists of the water in the emulsion plus moisture in the ag- where moisture loss is expected to be least rapid, such as shady gregate chips, but not moisture in pavement). Moisture con- or cooler locations. Caution should be exercised when imple- tent of the chip seal should be measured in areas of the proj- menting this practice since it is based on limited research. Using ect where moisture loss is expected to be slowest (e.g., shady vacuum brooms or push brooms with nylon (not steel) bris- or cooler locations).