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54 rates. The most important reason for scrutinizing field appli- determine if the proper embedment is being obtained. Many cation is to ensure that application rates are within the toler- agencies perform embedment checks in the field. In practice, ances of the project's design standards. The field inspector aggregate is removed from the freshly constructed seal, and scrutinizes the binder application during construction. Imme- the percentage of embedment of the average chip is subjec- diately preceding and following each shot, a procedure known tively estimated (Janisch and Gaillard 1998). A 50% embed- as "strapping the distributor" occurs, which involves measur- ment after initial rolling and a 70% embedment after 2 or ing the amount of binder remaining in the distributor's tank more weeks of traffic application are typically recommended and allows the inspector to calculate the actual rate of binder (Jackson et al. 1990). If adequate embedment is not achieved being applied (A Basic Emulsion Manual 1997). This field owing to inadequate rolling, the chip seal will be susceptible to test means that the amount of binder remaining in the tank is raveling between wheelpaths and along edges of the lane where measured to determine precisely how much binder was used the lowest levels of embedment are present as a result of less on every shot. traffic action (Jackson et al. 1990; Gransberg et al. 1998). The North American philosophy toward chip seal appli- cation rates is that the chip seal design process can be used CONSTRUCTION CONCLUSIONS AND BEST PRACTICES only as a guideline; the actual binder application rate must be verified in the field. The main responsibility of the project's Construction was the one area in which best practices are inspection personnel is to verify if the binder and aggregate plentiful. This underscores the idea that there is only one rates are being properly applied. In addition, these personnel chance to properly construct chip seal projects. As a result, generally need to be knowledgeable about how to adjust both the literature review and the survey responses offered material application rates to account for localized variations many examples of practices that can be observed to achieve in road surface characteristics. Survey respondents were successful chip seal projects. Thus, there is one overarching requested to provide the application rate tolerances they typ- conclusion for this chapter. Both the agency and the contractor ically allow for in their contracts. A common response is to must understand the chip seal construction process and be pre- allow a tolerance rate of ±10% for aggregate spreading and pared to execute the project in strict observance to the required ±5% for binder application. procedures. This conclusion is underscored by the responses from agencies that use chip seals on high-volume traffic roads. Those responses were from agencies that not only Monitoring Construction Operations rated their chip seal performance as good or excellent, but they were also from agencies that applied a more detailed set Field inspection responsibilities include ensuring that con- of specifications to the construction process. In other words, struction operations are conducive to high-quality workman- those agencies see chip seal as a science that can be repli- ship specified in the contract. Perhaps most important, every cated through adherence to strict technical guidelines during distributor shot needs to be carefully observed to monitor a construction, rather than as an art that must follow a recipe number of spray characteristics. The operation of the distribu- to work properly. tor is judged by visual observation. A uniform application both in the transverse and longitudinal directions is particularly Another conclusion deals with the importance of the roller important in chip seal work. Streaking is the most observable to chip seal success. The idea that the rolling can be ignored characteristic and is usually caused by one of the following because the rollers are not trying to achieve a specified level four conditions: applying the binder at an inappropriate tem- of compaction is without merit. The major mode of early chip perature, high binder viscosity, improper spray bar height, or seal failure is loss of aggregate. The rolling operation is the incorrect pump pressure. Fan patterns and the appearance of a tool in the chip seal paving train that ensures that proper ini- "uniform sheet of binder" need to be observed (Gransberg tial embedment is achieved. Therefore, greater attention must et al. 2000). Desired fan width is usually obtained with a dou- be given to both the specifications for rolling and inspections ble lap and needs to be equal for all nozzles (Asphalt Surface in the field to ensure that those specifications are being met. Treatments--Construction Techniques 1988). Because the roller is the slowest member of the chip seal train, it is critical to ensure that a sufficient number of rollers are The actual rate of aggregate spread needs to be regularly both furnished and maintained, so that the aggregate is embed- compared with the design rate, to ensure that overapplication ded when the binder is as soft as possible and, in the case of is not occurring. Experienced field personnel can generally emulsions, before the emulsion has broken, as indicated with a observe any variation. It is essential that a uniform "curtain" color change from brown to black. of aggregate be applied across the entire binder shot width (Gransberg et al. 2000). Recognition that chip seal construction QC is very visual should not be contested. However, many performance con- The depth at which the aggregate is embedded into the cerns do not appear during construction. Therefore, a QA/QC binder should be continuously monitored during rolling. For program for chip seals needs to consist of more than just qual- the chip seal to be successful, the inspector must be able to ified personnel; it must also be a well-planned system of sci-
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55 entific tests and engineering principles to ensure that quality 9. Have the most experienced inspector predrive each materials conform to performance expectations. Additionally, shot and paint binder rate adjustment on the pavement it is very difficult to correct an error that was made during to facilitate field rate adjustments. chip seal construction. The contractor must literally get it 10. In areas where extensive stopping and turning move- right the first time. A number of best practices were observed ments take place, the application of a small amount of in this area: excess aggregate may reduce scuffing and rolling (Janisch and Gaillard 1998). The use of a racked-in seal 1. All types of chip seals are best applied in the warmest, (see Figure 13) as used in Australia and South Africa driest weather possible. may be a viable engineered solution for determining the 2. Ambient air temperature at the time of application precise amount of aggregate for these problematic areas. should be a minimum of 50°F (10°C) when using emul- 11. Rolling guidelines and specifications for roller cover- sions, and 70°F (21°C) when using asphalt cements with age, rolling patterns, and minimum rolling time or a maximum ambient air temperature of 110°F (43°C). passes achieve full lane coverage and a similar num- 3. The temperature of the surface should be a minimum ber of passes for all areas of the lane (see Table 9). of 70°F (21°C) and no more than 140°F (54°C) when Minimum rolling times are generally in the range of using emulsions. 3,000 to 5,000 yd2/h. 4. Complete patches at least 6 months in advance and 12. The required number of rollers is a function of desired apply crack seals at least 3 months before the applica- binder distributor production and required rolling tion of chip seals. time or passes for each shot width on the project. 5. Variable nozzles permit the application of a reduced 13. Have rolling follow as closely as practical behind the rate of binder in the wheelpaths and combat flooding aggregate spreader. in the wheelpaths, a defect that makes chip seals prone 14. Do not sweep the loose aggregate from the roadway to bleeding. Conversely, the Australian use of pre- immediately following rolling, because the residual spraying is another method for adjusting the trans- binder has not yet cured enough to bond to the aggre- verse surface texture of a pavement surface before gate and underlying road surface. Accordingly, it is construction of a chip seal. important to control the sweeping and not dislodge the 6. Either hand-raking or drag-brooming can correct minor embedded aggregate particles from the binder. aggregate spread deficiencies such as corrugation, 15. Maintain traffic control for as long as possible to give uneven spread, or missed areas. the fresh chip seal the maximum amount of curing 7. Aggregate should be applied as quickly as possible time before opening it to traffic. with both emulsified and asphalt cement binders. Wait- 16. Assign experienced personnel who understand the ing for the emulsion to break reduces the effectiveness dynamics of chip seal construction as field QC and of the rollers in achieving the desired embedment depth QA persons. of the aggregate. 17. Regularly calibrate both the distributor and the chip 8. The Montana field-sweeping test (Maintenance Chip spreader. Seal Manual 2000) curtails the bias to spread excess 18. Evaluate aggregatebinder compatibility tests, as shown aggregate created by paying for it by the ton. Montana in Table 12, for local appropriateness and before and requires that the amount of excess chips be less than during construction. 10% of the design rate and adjusts the pay quantities 19. Field test binder at both the distributor and aggregate based on the sweeping test results. This may also stockpiles daily to ensure that material has not degraded reduce the potential for windshield damage claims. as a result of handling during transportation.