Tack Coat Specifications, Materials, and Construction Practices (2018) / Chapter Skim
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Pages 48-71
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From page 48... ...
Survey Results 51 for tack coats, but did not estimate the percentage used and was therefore not included in the weighted percentages. The same methodology was applied to weight the Canadian survey information, which tracked similarly to U.S.
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From page 49... ...
52 Tack Coat Specifications, Materials, and Construction Practices Manitoba, and Yukon reported using one product exclusively (CSS-1h, SS-1, and EP-2000, respectively)
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From page 50... ...
Survey Results 53 Agencies were asked whether or not they specified different application rates for different surface types, and if so, what the rates were in terms of residual asphalt.
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From page 51... ...
54 Tack Coat Specifications, Materials, and Construction Practices The survey results show that most often, the agency decides both what the tack coat material will be, and at what rate it will be applied. This was the case in all but one of the responding Canadian provinces and territories, and 62% (31/50)
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From page 52... ...
Survey Results 55 Another question about agency tack coat applications is whether or not dilution of the tack coat emulsion is allowed. The survey results showed that the number of agencies allowing dilution was fairly evenly split, with slightly less than half of U.S.
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From page 53... ...
56 Tack Coat Specifications, Materials, and Construction Practices for Canadian agencies tracked very closely with U.S. agencies.
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From page 54... ...
Survey Results 57 Figure 50 shows how often agencies verify the dilution rate. Some of the comments that provided further insights about verifying the dilution rates are as follows: a few states verify by some quantity, either once every given number of tons, or once per tank; Arizona accepts a certification from the supplier once per project, but also takes daily samples.
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From page 55... ...
58 Tack Coat Specifications, Materials, and Construction Practices Regarding the maximum time tack coat can be exposed before it must be covered by asphalt, the agencies offered comments about their specification. Three agencies (about 5%)
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From page 56... ...
Survey Results 59 off the tack, requiring the use of a spray paver, and retacking as needed. Figures 53 and 54 show the survey responses.
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From page 57... ...
60 Tack Coat Specifications, Materials, and Construction Practices each agency if they required tack coat before every lift. If they sometimes waive the requirement for every lift to be tacked, they were asked to estimate what percentage of surfaces were tacked prior to being overlaid with an asphalt mixture.
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From page 58... ...
Survey Results 61 calibration (2/2) use their own method.
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From page 59... ...
62 Tack Coat Specifications, Materials, and Construction Practices did not provide specific numbers for spray bar height or angle of nozzles, stating "per manufacturer's recommendations." Note that most agencies reported more than one requirement. Fourteen of the states surveyed had verbiage in their specifications specifically calling for uniform tack coat coverage.
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From page 60... ...
Survey Results 63 performance on subsequent applications. Seven agencies responded that they have no specified response to non-uniform tack coat applications.
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From page 61... ...
64 Tack Coat Specifications, Materials, and Construction Practices In the United States, slightly more than half of the responding agencies that use spray pavers said that they require a different type of tack coat material when using spray pavers. Canada was 50/50, but it should be noted there were only two provinces responding that spray pavers were an allowable option (Figure 63)
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From page 62... ...
Survey Results 65 machine ground speed/production rate to be no less than 30 feet per minute.
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From page 63... ...
66 Tack Coat Specifications, Materials, and Construction Practices The number of states that perform bond testing has seen an increase since the worldwide survey conducted as part of NCHRP Project 9-40. NCHRP Report 712 reported that 8% of agencies perform testing to measure the bond strength between pavement layers (Mohammad et al.
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From page 64... ...
Survey Results 67 Eight out of the 12 responding states indicated that they are using a laboratory shear testing apparatus for interface bond testing (Figure 68)
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From page 65... ...
68 Tack Coat Specifications, Materials, and Construction Practices (tension) by one state, 0.2 in./min (shear)
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From page 66... ...
Survey Results 69 limit. In Virginia on milled surfaces, a 100 psi (690 kPa)
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From page 67... ...
70 Tack Coat Specifications, Materials, and Construction Practices One province and five states are determining the percent of residual asphalt found in their samples. A penetration test is run on the residual in the same province and in two states.
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From page 68... ...
Survey Results 71 11. Oregon recently completed report SPR 782, "HMAC Layer Adhesion Through Tack Coat" (Coleri 2016)
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From page 69... ...
72 As indicated in Chapter 3, interface bond testing is a used by 12 states and one province. Of the 12 states, three were identified by the synthesis consultants and the NCHRP Project 20-05/ Topic 48-02 panel as candidates for case examples.
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From page 70... ...
Case Examples 73 Fiscal Year Centerline Miles Let with Bond Test 2017 345 2016 80 2015 399 2014 559 2013 291 2012 189 2011 67 Table 9. Kansas centerline miles let with bond tests by fiscal year.
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From page 71... ...
74 Tack Coat Specifications, Materials, and Construction Practices large improvement on the contractors' practices of applying tack. They are setting an application process that our field inspectors can monitor.
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