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OCR for page 41
42 indicates that surface preparation activities such as patching and crack sealing be completed "the previous autumn" before the year the chip seal will be applied (Design Guide . . . 1996). In contrast, the Indiana DOT states that patches must be com- pleted not less than 10 days before a chip seal (Seal Coat Placement 2003). Preconstruction Sweeping Preconstruction sweeping with rotary broom sweepers often creates considerable dust. If dust poses a danger to the trav- eling public, a flush truck may be employed to keep dust to a safe level. Preconstruction sweeping is performed to remove any dirt, dust, or debris from the existing pavement surface. (a) (b) Adequate sweeping will provide the necessary clean surface FIGURE 44 (a) Before and (b) after image of water retexturizing. that permits good adhesion with the bituminous binder. It is important that the full width of the existing surface be swept to remove all foreign material to ensure a clean surface before application of a chip seal (Asphalt Surface Treatments-- ing Guide 2004). An AASHTO scan tour report recommended Specifications undated). If the surface is swept too far in that this and other Australian chip seal techniques be investi- advance, it may need to be swept again on the day of con- gated for use in the United States (Beatty et al. 2002). struction. Figure 43 shows a typical rotary broom sweeper engaged in this task. Transit New Zealand's belief in the value of water retex- turing to prepare existing bleeding surfaces is exemplified by the following statement from the agency's chip seal manual: Water Retexturizing Texturing seal coats . . . can be expected to provide a service The restoration of texture to a road surface that is slick with life of up to 75% of the normal reseal [chip seal] life, ensur- excess binder can be performed by the use of the water- ing a satisfactory surface for resealing [chip sealing] at the retexturizing machine as shown in Figure 40. Its results are end of that period (Notes . . . 2002). shown in Figure 44a and b. In addition to restoring road sur- face texture before chip sealing is done, water retexturizing could be used as a repair technique for a bleeding surface with Prespraying poor skid resistance. Logically, care needs to be taken when water retexturizing to prevent nonexcess binder from being Australia and New Zealand have identified prespraying as a removed or stripped from the aggregate, because such a situa- method for adjusting the transverse surface texture of a pave- tion could invariably create a greater problem (Sprayed Seal- ment surface before construction of a chip seal. Surfaces that have significant disparity in binder content between wheel- paths and non-wheelpaths can be corrected with this technique. The areas outside of the wheelpaths are sprayed with an appli- cation of binder sufficient to increase binder content so that it is consistent with the texture of the wheelpaths. The spray run must be carefully planned to circumvent spraying the already binder-rich wheelpaths with additional binder (Sprayed Seal- ing Guide 2004). As is shown in Figure 45, the Australians prespray two lanes of traffic in one pass. Binder-deficient areas such as the centerline joint, the area between wheelpaths, and shoulders are typically sprayed. This technique and water retexturing are done to allow a constant rate of binder to be shot when applying the chip seal, thus eliminating the need to adjust binder and aggregate rates in the field. SPRAYING OPERATIONS Before spraying the binder, a number of procedures should FIGURE 43 Rotary broom sweeper preparing surface for sealing. be followed to ensure an accurate application:

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43 spraying correctly. Scrutinizing the binder distribution will ensure that any spraying problems, such as a clogged nozzle, nonparallel nozzles, or improper application temperature are mitigated immediately. Distributor Production Characteristics The chip seal system production rate is constrained by the FIGURE 45 Prespraying of areas outside wheelpaths. asphalt distributor's ability to apply the binder. Therefore, every other component in the chip seal equipment train must at least be able to equal the distributor's sustained production Determine distributor velocity and pump speed; to maximize the system's sustained production (Peurifoy et al. Delineate the distributor shot (limits); Construct paper joints; 2001). Observations in the field confirm that the distributor Blow out nozzles to make sure that none are plugged; sets the production rate for the rest of the equipment fleet Ensure proper transverse alignment of distributor; (Gransberg et al. 1998). As a result, the types and numbers and of each category of equipment must be carefully determined Ensure that binder temperature is within specification to ensure maximum production, minimum disruption to the limits. traveling public, and desired quality in the finished product. If there are not enough dump trucks, the aggregate spreader The distributor cannot begin spraying the binder until will lag behind the distributor, allowing the binder to cool all other required equipment has been prepared. The aggre- before application of aggregate. This can create the potential gate spreader, dump trucks, and rollers must be in position for raveling owing to lack of sufficient adhesion between the to begin their functions. A paper joint needs to be placed aggregate and the binder. at the beginning of the shot so that the distributor not only attains the proper application speed on crossing the paper If a project uses two distributors at the same time, the dis- joint, but also to provide a neat line and avoid a double tributors' production rate may be greater than that of the application of binder at the construction joint. At confir- aggregate spreader. It is essential that this not become a prob- mation that the distributor's transverse alignment is per- lem, and in concurrence with the practice illustrated in Fig- pendicular to the centerline, the binder application can ure 47, that the distributor not advance far in front of the commence (Figure 46). The binder application should aggregate spreader. The Asphalt Institute recommends not appear as a uniform sheet of binder across the entire width applying more binder than can be covered with aggregate of the shot. within 1 min (Asphalt Surface Treatments--Construction Techniques 1988). The operator should always strive to keep One of the most important factors in any spraying operation a minimal distance between the distributor and chip spreader is to visually inspect each shot to ensure that all nozzles are (Maintenance Chip Seal Manual 2000). FIGURE 46 Spray bar applying bituminous binder. FIGURE 47 Aggregate spreader within proximity of distributor.