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OCR for page 50
51 FIGURE 54 Chip seal construction practices for distressed pavements (adapted from Peshkin et al. 1999). LABORATORY DESIGN AND MATERIALS TESTING a binder that is incompatible with the aggregate. The compat- ibility of aggregatebinder combinations should be tested in Chip seal material testing should be performed both in the lab- the laboratory (Yazgan and Senadheera 2003). Table 12 illus- oratory and in the field. In regard to quality, it is essential that trates the aggregatebinder compatibility tests identified in an aggregate sample be provided to the materials laboratory the literature review. performing the design of the chip seal. The critical reason for providing binder and aggregate samples during the design phase is to ensure that the binder is compatible with the aggre- FIELD TESTING gate selected for use on the project. Failure to design the chip seal based on the binder and aggregate that the contractor will There is a significant material testing QA and QC concern in use could lead to failure if the specifications require the use of regard to aggregate testing in the field. With chip seal material

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52 TABLE 11 QUALITY CONTROL TESTS FOR CHIP SEALS Name of Test Property Measured Standard Test Number Manufacturing Control Sieve analysis Gradation AASHTO T26, ASTM C136 Cleanness value Fine materials Caltrans Test 227 No. 200 washed sieve Fine materials AASHTO T11, ASTM C117 Foreign materials Clay and friable particles AASHTO T19, ASTM C29 Decantation Dust Tex-217-F, Part 1 Plasticity index Deleterious material AASHTO T90, ASTM D4318 Aggregate Soundness Los Angeles abrasion Abrasion resistance AASHTO T96, ASTM C131 British pendulum test Skid resistance AASHTO T278, ASTM E303 British wheel Polishing AASHTO T279, ASTM D3319 Sodium sulfate loss Freezethaw degradation AASHTO T104, ASTM C88 Magnesium sulfate loss Freezethaw degradation AASHTO T104, ASTM C88 Aggregate Shape Percent fracture Roundness ASTM D5821 Flakiness index Flatness/elongation ASTM D4791 Asphalt Binder Emulsion penetration Penetration ASTM 244 Emulsion viscosity Saybolt viscosity ASTM 244 Emulsion sieve test Gradation ASTM 244 Asphalt cements Penetration AASHTO M226, ASTM D3381 Float test Drain-off, high float AASHTO T50, ASTM D139 testing, most aggregate properties are considered only in the North American respondents and 75% of overseas respon- design process. In general, survey responses indicated that dents perform field tests on their binders. field sampling is very limited for aggregates. If the aggregate is to be stockpiled on site or at a local plant, it is important to test samples from the pile to ensure that the material has not Qualified Field Personnel been susceptible to segregation or degradation during the period following its manufacture. Aggregate transport and Engineers or other qualified personnel generally administer the stockpiling can significantly alter the gradation of aggregate quality management program during the construction phase of and generally increase the amount of fine material in the a chip seal project. Generally known as field inspectors, these aggregate (Gransberg et al. 2000). In such conditions, the personnel ensure that specifications are being adhered to and original gradation of the stockpile can adversely change. specified quality standards are met. A noteworthy feature of However, it is intuitive to carry out field sampling, especially chip seal construction is the requirement for knowledge and in regard to gradation, at the stockpile site. In addition, the judgment in forming decisions that are the result of those only logical way to confirm that the same materials tested in same site-specific conditions that have caused many authori- the laboratory are being used for the project is to perform ran- ties to perceive chip sealing as an art (Wegman 1991). In terms dom samples at either the stockpiles or from the aggregate of field inspection personnel, an important distinction between spreader applying the material. North American and international practices results because U.S. and Canadian agencies do not adjust surface texture In addition, binders can become contaminated by foreign before the construction phase of the project. Some road surface substances inside the tanks of transports. Survey responses conditions may require that adjustments be made during indicated that field testing of binders is more prevalent than binder application. These adjustments are sometimes quite is field testing of aggregate. Figure 55 shows that 44% of subjective, with the magnitude of the adjustment based on an TABLE 12 AGGREGATEBINDER COMPATIBILITY TESTS Name of Test Agency Characteristic Aggregate Retention TxDOT, Tex-216-F Light sweep test Vialet French Public Works Inverted tray, ball impact Pennsylvania Retention Pennsylvania DOT Inverted tray, sieve shaker BST Sweep ASTM WK139 Replicates sweeping Film Stripping Caltrans and San Diego Aggregate-emulsion County, CT 302 compatibility Macrosurfacing Sweep Koch Materials TM101 Replicates sweeping

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53 100% 100% 75% 80% 100% 75% 56% 60% 44% 80% 40% 25% 60% 25% 40% 20% 20% 0% North America AU, NZ, UK, SA 0% North America AU, NZ, UK, SA Yes No Yes No FIGURE 55 Proportion of agencies performing field tests on binders. FIGURE 56 Proportion of agencies requiring distributor calibration. individual's experience. Therefore, a considerable portion of spreader is ASTM D5624, Standard Test Method for Deter- the field inspector's responsibilities are to adjust the applica- mining the Transverse-Aggregate Spread Rate for Surface tion rates as the texture of the pavement's surface changes Treatment Applications. Figure 57 shows a significant dis- (Janisch and Gaillard 1998). As a result, North American parity in philosophies concerning aggregate spreader cali- field personnel have an expanded role in comparison with bration; the overseas respondents show little concern with their international counterparts. their aggregate application, with only 29% of these agencies requiring spreader calibration. In general, qualified personnel need to be responsible for the following: When the survey results for both the binder distributor and aggregate spreader calibration are taken together, they show Ensuring that all equipment is calibrated, a fairly widespread disregard for basic QC practices in the Sampling and testing of materials, chip seal project. Perhaps this finding accounts for the per- Verifying material application rates, and ception that chip seal is more art than science and for that rea- Monitoring construction methods. son it cannot be reliably designed and applied. A number of the states reporting that they no longer use chip seals cited uncontrollable variability as their reason for discontinuing its Calibrating the Distributor use. Perhaps adopting the best practices identified in this report could reduce this variability. To maintain accuracy, several calibration procedures and checks should be regularly performed on the binder distrib- utor. Calibrating the binder distributor ensures that the dis- Verifying and Adjusting Material Application Rates tributor spray bar is applying the appropriate designed appli- cation rate from each nozzle, and that the spray bar height is The methods used to verify actual application rates have been correct so that that the appropriate fanned spray pattern identified. Respondents also provided details of their policies results. A standardized method for calibrating the transverse toward accepted tolerances allowed for binder and aggregate application rate of a distributor can be found in ASTM 2995, Standard Recommended Practice for Determining Applica- tion Rates of Bituminous Distributors. Given the significant quality issues that derive from accurate binder application, 71% Figure 56 shows that 25% of North American agencies do 80% 62% not require the distributors on their projects to be calibrated. 60% 38% 29% 40% Calibrating the Aggregate Spreader 20% The calibration of the aggregate spreader is crucial to the sat- 0% isfactory performance of chip seals (Janisch and Gaillard North America AU, NZ, UK, SA 1998). Calibrating the aggregate spreader ensures that all gates are applying the same rate of aggregate across the Yes No entire spread width and therefore that the aggregate spreader is applying the desired amount of aggregate per square yard. FIGURE 57 Proportion of agencies requiring spreader The recommended procedure for calibrating an aggregate calibration.