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37 FIGURE 37 Pneumatic roller tire configuration. to "tighten it up" and create a uniformly prepared surface (McLeod 1969). Steel-wheeled rollers will have difficul- ties when the underlying pavement is rutted, because they will bridge over the ruts and fail to properly seat the aggre- FIGURE 38 Typical rotary broom. gate in the wheelpaths. Other Roller Types chip seal, but they are more likely to dislodge embedded aggregate after construction. Plastic bristles require earlier The other types of rollers are variations on either the pneu- replacement; however, they are not as likely to damage the matic or steel-wheeled roller. The rubber-coated, steel-wheeled new chip seal. roller has a layer of rubber attached to the drum and causes less damage or degradation to the aggregate while retaining Rotary brooms generate dust, which can affect visibility the high contact pressure inherent to the static steel-wheeled for traffic. Additionally, they move the excess aggregate to roller. With the vibratory steel-wheeled roller, the machine the side of the road, where it can eventually be swept back vibrates as it rolls and is thought to better seat the aggregate onto the traveled way by either rain or vehicles using the owing to the vibration's effect. Finally, the combination shoulder for parking. pneumatic and steel-wheeled roller has a set of pneumatic tires on one end and a steel drum on the other. This piece of equipment attempts to combine the advantages of both roller Pickup and Vacuum Sweepers types in a single machine. Pickup sweepers are generally used wherever dust must be minimized and it is desirable to remove all excess aggregate SWEEPING EQUIPMENT from the project limits. A pickup sweeper features a broom that sweeps the aggregate to a suction head that deposits the There are two main tasks for sweeping on a chip seal project: material in a storage tank. Pickup sweepers are particularly cleaning the existing road surface of dust and foreign materi- useful in urban areas where aggregate accumulation in gut- als before placing the chip seal and removing excess aggregate ters or along the edge of the roadway is undesirable. Vacuum from constructed chip seals. There are three different types of sweepers represent purpose-built equipment that removes the sweeping equipment typically used in chip seal construction: excess aggregate through suction only. The lack of contact rotary brooms, pickup sweepers, and vacuum sweepers. with the chip seal's surface minimizes damage and is the pre- ferred method of loose aggregate removal in Australia (Sprayed Sealing Guide 2004), as well as in some parts of the Rotary Brooms United States. Rotary brooms, such as the one shown in Figure 38, are employed to remove the excess aggregate from the surface of UNIQUE EQUIPMENT the chip seal without dislodging the embedded particles. The downward pressure must be kept to a minimum as the An effort has been made to associate construction methods broom's bristles will remove the aggregate with a flicking with unique pieces of construction equipment. Thus, a num- action. The main concern with rotary brooms pertains to bris- ber of pieces of equipment that are not found in North Amer- tle selection. Steel bristles are unquestionably more success- ica have been identified and are described here to furnish ful than other types in removing foreign materials from the information to agencies that may be looking for new solu- surface of the existing pavement surface before placing the tions to their chip seal equipment concerns.
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38 Aggregate Precoating Loader Precoating of aggregate with a purpose-built aggregate loader is a common practice in Australia and New Zealand (Sprayed Sealing Guide 2004). The loader is a unique piece of equip- ment that takes windrowed aggregate in one end and screens out the dust. It then precoats the aggregate through a trom- mel screen and loads the precoated aggregate directly into the dump trucks. VicRoads, an Australian road agency equiva- lent to an American state DOT, contends that using front-end loaders is not acceptable for loading chip seal aggregate owing to the increased fines associated with aggregate degra- dation during handling (Bituminous Sprayed Surfacing Man- ual 2003). Figure 39 shows this special piece of equipment in operation. FIGURE 40 Low-drop aggregate spreader. Low-Drop Aggregate Spreader Water-Retexturizing Machine Low-drop aggregate spreaders are used in Australia. This A water-retexturizing machine can eliminate the effects of machine was developed to minimize the bouncing and turning bleeding by using carefully directed high-pressure water to of aggregate as it hits the freshly shot surface. It is believed that remove any binder that is submerging the aggregate on the this machine increases the uniformity of the aggregate's spread existing surface. These machines have been used in Aus- by placing it as close to the surface as possible. From Figure 40, tralia and the United Kingdom to treat bleeding surfaces. one can see that the operator is facing forward, which also con- Such equipment is especially valuable for preparing the tributes to better control of the aggregate spreading operation. surface of the road before receiving a chip seal. Figure 41 illustrates a water-retexturizing machine in use in the United Kingdom. Rubber-Coated Drum Rollers Rubber-coated drum rollers are purpose built for chip seal Combination Vibratory Pneumatic Rollers operations. The rubber coating supposedly reduces the crush- ing of the aggregate inherent with steel-wheeled rollers, Finally, none of the respondents indicated that they used while achieving the embedment and mosaic characteristics combination vibratory pneumatic rollers, probably owing not capable with a pneumatic roller. The survey responses to the recent development of the rollers. Trials of vibratory indicated that rubber-coated drums are commonly used on pneumatic rollers are suggested, because they are specif- chip seals (known as surface dressings in British terminol- ically designed for achieving both the benefits of aggregate ogy) in the United Kingdom, and they are also used when particle orientation and embedment compaction. They appear required on sprayed seals in Australia. British Columbia was to offer some significant advantages to standard pneumatic the only North American agency that prescribes the use of rubber-coated drum rollers. FIGURE 39 Aggregate precoating loader. FIGURE 41 Water-retexturizing machine.