Cover Image

Not for Sale

View/Hide Left Panel
Click for next page ( 33

The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement

Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.

OCR for page 32
33 CHAPTER SIX EQUIPMENT PRACTICES INTRODUCTION 1. Insulated asphalt tank, 2. Heating system and circulation pump, The quality of the equipment and the appropriate use of its 3. Spray bar and nozzles, and capabilities undoubtedly play roles in successful chip seal proj- 4. Distributor controls and gauges. ects. This chapter explores the state of the practice in chip seal equipment selection and use. For this synthesis study, particu- lar attention was paid to the types and sizes of equipment typ- Insulated Asphalt Tank ically specified. The survey responses and literature review identified a number of equipment technologies being widely The distributor's tank must be capable of efficiently storing the used abroad, with which North Americans have little familiar- binder at temperatures that allow the heated binder to remain ity or expertise. They are discussed at the end of the chapter. consistent with the appropriate viscosity for spraying opera- tions and within the design specifications. Most of the asphalt The following major types of equipment are typically distributor tanks used for chip seal work hold from 1,000 to used on all chip seal projects: 4,000 gal of liquefied asphalt. They should be equipped with baffles to prevent pressure surges resulting from the asphalt Asphalt binder distributors, sloshing in the tank when starting and stopping. Aggregate (chip) spreaders, Rollers, Dump trucks, and Heating System and Circulation Pump Sweeping equipment. Depending on the make and size of the distributor, either one or two burners are used. These burners are supported at the BINDER DISTRIBUTOR rear of the tank and positioned with a configuration that directs the flames into the insulated tank's flues. A constant The binder distributor is essentially an asphalt tank with spray- volume circulation pump maintains a pressurized system so ing equipment mounted on a truck chassis. Analysis of binder that the binder can be uniformly heated. The circulation distributors has paid particular attention to binder distributor pump must also spray a constant volume for the entire length components, production characteristics, controls and calibra- of the spray bar for each application. In addition, the pump tion, and spraying operations. The binder distributor has gone enables the distributor operator to load the tank with binder through some significant technological advancements, with from a storage tank. most manufacturers now offering binder distributors with par- allel spray bars (also called wheelpath bars) that enable vari- able spray rates across the lane. In this discussion, particular Spray Bar and Nozzles attention is being paid to the binder distributor, with a special focus on the use of variable nozzles and multiple spray bars. Figure 30 shows a typical distributor spray bar. There are The use of computerized distributors is becoming more com- many different bar widths available, with typical spray bars mon in North America, with 63% of agencies in Canada and on North American distributors being 12 ft wide, whereas the United States requiring computerized rate-controlled dis- agencies that prespray as a method of surface preparation use tributors in their specifications, as shown in Figure 29. Inter- spray bars as wide as 24 ft (Sprayed Sealing Guide 2004). national specifications requiring computerized distributors appear to be more stringent, with 88% of international respon- Spray bars connect a series of evenly spaced nozzles dents indicating that they mandate this technology. along its length. Nozzles are manufactured with different sizes of openings to permit different volumes to be pumped from the same pump pressure. The nozzles control the spray Distributor Components pattern of bituminous binder shot from the distributor. Appropriate selection of nozzles is critical to achieving a A straightforward way of understanding a distributor is to consistent and accurate spray pattern. Nozzles with larger break it down into its four essential components: openings need to be considered for viscous asphalts such as

OCR for page 32
34 88% 100% 80% 63% 63% 60% 37% 37% 40% 12% 20% 0% United States Canada AU, NZ, UK, SA Yes No FIGURE 29 Respondents requiring computerized distributors. crumb-rubber binders (Sprayed Sealing Guide 2004). One it ensures a uniform distribution of binder across the shot may be able to modify the spray bar on the asphalt distribu- width and that no areas are missed. However, to do so, the tor so that it has smaller nozzles in the wheelpaths, a practice spray bar must be adjusted to the correct height or the spray that results in more binder in the nontraffic areas than in the pattern will become distorted. A spray bar with a positive traffic areas (Gransberg et al. 1998). The nozzles are installed shutoff called a cut-off valve will avert problems with noz- in the spray bar so that the fan-shaped spray is at an angle to zle dribbling. This is particularly important on the end noz- the axis of the spray bar. The angle varies from manufacturer zles, which might also be equipped with a deflector to to manufacturer. Figure 31 shows that this angle is usually develop a sharp edge on each side of the shot or by changing between 15 and 30, depending on the manufacturer. All the angle of the end nozzles. nozzles must be set at the same angle to avoid distortion of the spray pattern. Distributor Controls and Gauges The spray bar and nozzles are designed to provide an appropriate fan width to ensure uniform transverse distribu- Typical controls and gauges include tachometers, volume tion, without any corrugation or streaking. Chip seal projects measuring devices, pressure gauges, and a thermometer. In require either double- or triple-lap coverage, as shown in Fig- addition, most distributors manufactured today have comput- ure 32. The advantage of using double or triple lapping is that erized systems that not only regulate the pressure of the mate- rial to compensate for the speed of the vehicle, but also allow the operator to quickly make accurate rate adjustments, adjust the spray bar height and width, and even shut off individual spray bar sections from the cab. Before the development of computerized rate control systems, a distributor would require more than one operator. Figure 33 shows a contem- porary computerized control panel for a binder distributor. Such a panel is capable of allowing the operator to control all distributor operations from the cab of the distributor. FIGURE 30 Distributor spray bar. FIGURE 31 Spray bar nozzle alignment.