Tack Coat Specifications, Materials, and Construction Practices (2018)

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96 Tack Coat Specifications, Materials, and Construction Practices 14. Does your agency specify when traffic is allowed on the applied tack coat surface? If so, when? 0% (0/50) a. before the emulsion breaks (color change from brown to black) 16% (8/50) b. after the emulsion breaks 10% (5/50) c. after the emulsion has set (all the water has evaporated from the emulsion) 0% (0/50) d. after a specific time delay (for example, 30 minutes)—please state delay time 42% (21/50) e. traffic not allowed on fresh tack between distributor and paver 34% (17/50) f. does not specify 15. Does your agency specify when the paver is allowed to place asphalt on an emulsified tack coat? If so, when? 0% (0/50) a. before the emulsion breaks (color change from brown to black) 56% (28/50) b. after the emulsion breaks 12% (6/50) c. after the emulsion has set (all the water has evaporated from the emulsion) 0% (0/50) d. after a specific time delay (for example, 30 minutes) 32% (16/50) e. does not specify 16. What is the maximum time tack coat can be exposed before it must be covered by asphalt? 10% (5/50) a. hours – Most of these were 2 hours or less, one stated 1/2 day 2% (1/50) b. days – About 20% stated the same day or same shift, about 10% stated within 24 hours 46% (23/50) c. no limit – Most of these agencies have specification wording that tack must be kept clean, maintain the bonding ability, etc. 42% (21/50) d. other, please specify – write in (required): Most common responses were that tack must be covered the same day or the same work shift. 17. What is the maximum distance the tack coat can be applied in front of the paver? 2% (1/50) a. enter distance in feet – (only one response: 500 ft) 90% (45/50) b. no specification regarding maximum distance 16% (8/50) c. other, please specify: not so far as to lose adhesiveness, cover same day most common answers 18. Which methods does your agency use to minimize/prevent pickup of tack coat materials? (Check all that apply.) 56% (28/50) a. tack coat must break (color change from brown to black) before any type of traffic can be placed on the tack coat 18% (9/50) b. tack coat must set (all the water has evaporated from the emulsion) before any type of traffic can be placed on the tack coat 14% (7/50) c. requires the use of reduced-tracking tack materials 40% (20/50) d. allows the use of reduced-tracking tack materials 14% (7/50) e. requires the use of spray pavers 28% (14/50) f. allows the use of spray pavers 18% (9/50) g. sanding of tack coat materials after application 4% (2/50) h. allows wetting/dampening of pavement before application of tack 14% (7/50) i. other method, please specify: majority of “others” do not allow traffic on tack 54% (27/50) j. tracking or pickup continues to be a problem

Summary of Survey Results (U.S.) 97 19. On average, what percentage of the pavement surface do you estimate is tacked on your projects, given that improper tacking (application was attempted on the entire pavement surface, but stripes or untacked areas resulted) will result in less than 100% coverage? 10% (5/50) a. 100% coverage 42% (21/50) b. 90+% coverage 36% (18/50) c. 70–90% coverage 12% (6/50) d. 50–70% coverage 0% (0/50) e. < 50% coverage 20. Do you require tack before every lift of overlay (100%—every lift has the underlying surface tacked)? If your agency sometimes waives a requirement for every lift to be tacked before- hand, what percentage of surfaces do you estimate are tacked prior to being overlaid with an asphalt mixture? 72% (36/50) a. 100% (every lift has the underlying surface tacked) 22% (11/50) b. > 75% 6% (3/50) c. 25–75% 0% (0/50) d. < 25% 21. If your agency sometimes waives its typical requirement for tack coat, under what circum- stances would the requirement be waived? (Check all that apply.) 44% (22/50) a. second lift on “fresh” material 2% (1/50) b. asphalt pavement surface was milled prior to paving 0% (0/50) c. PCC pavement surface was milled prior to paving 14% (7/50) d. environmental conditions were deemed too poor 0% (0/50) e. nighttime paving 6% (3/50) f. other reason, please specify: small projects, wheel paths, base courses 44% (22/50) g. not applicable 22. If environmental conditions was one of your reasons above, please indicate which situa- tions keep tack coat from being applied. 4% (2/50) a. minimum ambient temperature (°F): 32, 40, 45, 50 0% (0/50 b. maximum ambient temperature (°F) – write in (required) _________ 6% (3/50) c. minimum pavement surface temperature (°F): 45, 50 0% (0/50) d. maximum pavement surface temperature (°F) – write in (required) _________ 8% (4/50) e. wet pavement surface 6% (3/50) f. damp pavement surface 6% (3/50) g. impending rainfall 2% (1/50) h. time of year 2% (1/50) i. other reason, please specify: dirty, unfavorable conditions 86% (43/50) j. not applicable 23. How often do you require calibration of a tack coat distributor? 36% (18/50) a. never 14% (7/50) b. annually 0% (0/50) c. monthly 18% (9/50) d. per job 32% (16/50) e. other, please specify: majority “when necessary,” one on new distributors 24. If calibration of the distributor is required, what method is required? (Percentages based on agencies that require calibration.) 13% (4/32) a. ASTM D 2995a 6% (2/32) b. ASTM D 2995b

98 Tack Coat Specifications, Materials, and Construction Practices 53% (17/32) c. agency standard, please specify – write in (required) _______________ 0% (0/32) d. not applicable 25. If calibration is required, who performs the calibration? (Check all that apply.) (Percentages based on agencies that require calibration.) 28% (9/32) a. The agency 44% (14/32) b. The contractor 16% (5/32) c. Independent testing firm 16% (5/32) d. Distributor manufacturer 3% (1/32) e. Other 0% (0/32) f. Not applicable (percentages based on agencies who require calibration) 26. During construction, how is the tack coat application rate checked? (Check all that apply.) 2% (1/48) a. ASTM D 2995a 0% (0/48) b. ASTM D 2995b 21% (10/48) c. mass applied calculation 56% (27/48) d. volume applied calculation 10% (5/48) e. agency standard, please specify – write in (required) ________________ 19% (9/49) f. application rate is not checked 27. Which of the following are specified by your agency for spray application of tack coat materials? (Check all that apply.) 2% (1/50) a. spray without overlap of emulsion streams on the application 18% (9/50) b. spray with double overlap of emulsion streams on the application 20% (10/50) c. spray with triple overlap of emulsion streams on the application 6% (3/50) d. minimum height (inches) of the spraybar: 1 state indicated minimum height of 11 inches 4% (2/50) e. maximum height (inches) of the spraybar: 1 state indicated maximum height of 12 inches 8% (4/50) f. minimum angle (degrees) nozzle angle relative to the spraybar 10% (5/50) g. maximum angle (degrees) nozzle angle relative to the spraybar 36% (18/50) h. clean nozzles 40% (20/50) i. uniform nozzles 38% (19/50) j. Other—most: “uniform distribution;” two: “100% coverage;” one: “even heat, pressure” 16% (8/50) k. none 28. If the tack coat is not uniform, what steps are employed to correct the problem? (Check all that apply.) 42% (21/50) a. make the contractor reapply tack coat at the same rate 50% (25/50) b. make the contractor reapply tack coat at a reduced rate 20% (10/50) c. penalize the contractor, please describe: do not pay for tack, reduce pay 18% (9/50) d. require the contractor to do better on subsequent applications, but do not require a reapplication of tack or enforce any penalty on the current application 44% (22/50) e. require the contractor to clean nozzles 10% (5/50) f. do nothing 20% (10/50) g. other steps not offered here, please describe – write in (required) ______ • most: “repair to the satisfaction of the Engineer” • one: “remove and replace” • one: “repair to manufacturer’s rep’s satisfaction” • reapply

Summary of Survey Results (U.S.) 99 29. Do any of the following conditions cause the specified residual asphalt tack coat application rate to change? (Check all that apply.) 2% (1/50) a. time of year 4% (2/50) b. time of day (day vs. night) 20% (10/50) c. type of roadway 50% (25/50) d. pavement surface condition 4% (2/50) e. ambient temperatures 0% (0/50) f. overlay thickness 12% (6/50) g. other, please specify – write in (required) ______________________ • Engineer can adjust application rate at any time • type of overlay • adjust within allowable range according to conditions • age of pavement • base condition 38% (19/50) h. no 30. Do your specifications and/or plan notes clearly state to apply the tack coat some distance beyond the planned mat width (to help confine the longitudinal joint)? 20% (10/50) a. yes 80% (40/50) b. no 31. Does your agency allow the use of spray pavers? (If no, proceed to question 36.) 56% (28/50) a. yes 44% (22/50) b. no 32. If so, on what percentage of your agency’s projects do you estimate they are used? 0% (0/28) a. 81%–100% 4% (1/28) b. 61%–80 % 0% (0/28) c. 41%–60% 7% (2/28) d. 21%–40% 89% (25/28) e. 0%–20% 33. Does your agency require a different type of tack coat to be used with spray pavers than on projects without spray pavers? 57% (16/28) a. yes 43% (12/28) b. no 34. If so, what tack material(s) is specified for use with spray pavers? • “polymer-modified emulsion” (generic answer): 8 states • CRS-1p: two states • PG 64-22: one state • “non-tracking tack” (generic answer): one state • EBL: one state • CSS-1h: one state • CSS-1: one state • CRS-1p: one state • CQS-1hp: one state 35. Does your agency require any specific methodology to ensure that the tack coat applied by spray pavers is uniform and at the proper application rate? 19% (5/27) a. yes: please describe the methodology • all but one state replied that it was done visually • one state: “The Polymer-Modified Emulsion Membrane shall be sprayed at a temperature of 140°F to 180°F. The sprayer shall

100 Tack Coat Specifications, Materials, and Construction Practices accurately and continuously monitor the rate of spray and provide a uniform application across the entire width to be overlaid. The tar- get application rate of the Polymer-Modified Emulsion Membrane shall be 0.20 gsy. Field adjustments to the target application rate of asphalt emulsion shall be determined based upon the existing sur- face condition of the pavement. No wheel or other part of the paving machine shall come in contact with the Polymer-Modified Emulsion Membrane before the hot mix asphalt concrete is applied. The paver shall be capable of applying the hot mix asphalt concrete following the spray of the Polymer-Modified Emulsion Membrane by no more than 5 s.” 81% (22/27) b. no Tack Coat Application Evaluation 36. Does your agency perform interface bond strength testing? (If no, proceed to question 42.) 24% (12/50) a. yes 76% (38/50) b. no 37. When does your agency perform interface bond strength testing? (Check all that apply.) 8% (1/12) a. routinely on every asphalt project for quality assurance/acceptance 17% (2/12) b. by special provision 58% (7/12) c. for product evaluation 75% (9/12) d. as part of forensic investigations 42% (5/12) e. other, please elaborate • approval method for reduced-tracking tack • as a referee method to resolve issues • required under PWL system • currently evaluating method 38. What type/style of interface bond strength testing does your agency perform? (Test criteria discussed in main body of report) 67% (8/12) a. lab shear testing 0% (0/12) b. field shear testing 8% (1/12) c. lab torsion testing 8% (1/12) d. field torsion testing 17% (2/12) e. lab tension testing 33% (4/12) f. field tension testing 0% (1/12) g. other testing 39. Is the stress applied: 0% (0/11) a. in a creep load (constant; neither increasing nor decreasing) to failure 100% (11/11) b. in a monotonically increasing stress or displacement rate to failure (constant rate of loading to failure) 0% (0/11) c. cyclical 0% (0/11) d. other 40. If a normal load is applied, is it required or optional? 27% (3/11) a. required 27% (3/11) b. optional 45% (5/11) c. not allowed

Summary of Survey Results (U.S.) 101 41. What minimum bond strength value do you require for your agency’s test method(s)? State test method and minimum bond strength required, including units. • One state: lab shear 70 psi minimum • Three states: lab shear 100 psi minimum • One state: field tension 35 psi minimum • Others: no answer or under development 42. Does your agency require any tests, either in the lab or in the field, to evaluate tack coat materials in lieu of or in addition to bond strength? 27% (13/49) a. yes: virtually all respondents referred back to standard emulsion testing in the lab 73% (36/49) b. no 43. For what types of pavement failures do you consider tack coat as a potential cause? 98% (48/49) a. Slippage of the surface layer 96% (47/49) b. Delamination of pavement layer 51% (25/49) c. Fatigue cracking 33% (16/49) d. Top-down cracking 12% (6/49) e. Rutting of the pavement 0% (0/49) f. Other distress(es), please describe (Required) _____________________ 44. Does your agency have any completed, ongoing, or planned research on tack coat materials or performance? Please describe or provide links to the projects or their reports. Thirty percent of U.S. agencies reported having ongoing, planned, or recently completed research in this area. Most of these research activities involve assessing the bond strength characteristics of tack coats. 45. Do you have additional comments regarding any aspect of tack coats you would like to include? The following are the additional comments: For dense-graded and SMA asphalt mixtures, our specifications appear to prohibit the use of spray pavers, but we allow spray pavers for “Ultra-Thin Bonded Wearing Course” (i.e., Novachip). In the literature, info on Reduced-Tracking Material seem to be scarce. It would be good to publish info (TechBrief?) on the RTM types, names, specs. etc. . . . performance case studies. . . . . The importance of a clean surface prior to application. There are still growing pains with non-tracking tack coat materials. They must be handled much more carefully than traditional tacks. Additionally, they are all proprietary. Many contractors do not like them. Until 2015, GDOT did not allow the use of emulsified asphalt as tack coat under asphaltic concrete pavement. We are now on the learning curve. We are exploring two options to better ensure bond. Spray Pavers to avoid the tracking issue or using a “hot-applied” tack that consists of VRAM material. We would like to see an AASHTO method that evaluates bond strength. With drier mixes, tack coats are more critical. When we paid for the asphalt as a separate bid item, the issues with pavement delamination or slippage did not seem to exist. Would like to see a practical bond or shear strength test that we could use to verify proper application and performance of tack coats.

102 Tack Coat Specifications, Materials, and Construction Practices Would like to see ideas for performance-based specification. What type of performance tests and what requirements. Also, development of a test method for evaluating less-tracking or non-tracking tack coats. We have a specification that is based on the pen value of the base asphalt but this still excludes many manufacturers. I have seen folks try to modify a test method for roadway paint but something on a national level would be nice. We use emulsion for fog seal, using PG 64-22 for tack coat of thin overlay.

103 Tack Coat Payment Specifications 2. How is tack coat paid for on your contracts? 86% (6/7) – individual pay item 14% (1/7) – incidental to paving 3. If it is paid as an individual item, how is it measured? (Check all that apply.) 0% (0/6) – volume of residual asphalt 0% (0/6) – mass of residual asphalt 50% (3/6) – volume of undiluted emulsion 17% (1/6) – mass of undiluted emulsion 0% (0/6) – volume of diluted emulsion 0% (0/6) – mass of diluted emulsion 33% (2/6) – other – write in (required): square meters Tack Coat Materials 4. Which types and grades of asphalt materials are commonly used for tack coat on your agency’s paving projects AND what percentage of your agency’s total tack coats do you estimate use the material? Use as many spaces as you need. Material types include results for agencies that only provided material type, percentages are based on the total of all materials (binders, emulsions, reduced-tracking) with agency-reported estimated percentages, and include weighted results for only those agencies that provided both material type and per- centage used. PG Binders Emulsified Asphalts Cutback Asphalts Reduced-Tracking Materials Other PG 58-28: NR* Non-standard: 25.5% Cleanbond: 0.2% PG 64-28: NR* CRS-2: 0.3% CRS-2p: 0.3% RS-1: 15.0% SS-1: 57.8% SS-1h: 0.9% * NR signifies that at least one agency reported using the material butdid not report a percentage used. 5. Check all that apply if your agency specifies a specific tack coat material for nighttime paving: No Canadian responses to this question A P P E N D I X C Summary of Survey Results (Canada)

104 Tack Coat Specifications, Materials, and Construction Practices 6. Does your agency specify different application rates for different surface types? Please supply the target or target range of the RESIDUAL ASPHALT application rates for each surface type. The table below represents the consultants’ best efforts to compile the responses. (Multiply l/m2 × 0.221 to convert to gsy.) Surface Type Tacked Residual Asphalt Application Rate (l/m2) Average Low Average High Average Target New Asphalt 0.129 0.167 0.148 Existing (Old) Asphalt 0.097 0.144 0.120 Milled Asphalt 0.097 0.144 0.120 New or Existing PCC 0.150 0.300 0.225 Milled or Diamond Ground PCC 0.200 0.275 0.238 Comments MTO application rates were converted from kg/m2 to l/m2 assuming a specific gravity for the emulsion of 1.00. Two out of seven provinces did not report any application rates. 7. Who decides what the tack coat type and application rate will be? 100% (7/7) a. agency or agency representative 14% (1/7) b. contractor (one agency responded “yes” to both agency and contractor) 0% (0/7) c. supplier 0% (0/7) d. other, please specify Tack Coat Application 8. What is required by your agency’s specifications for cleaning the pavement? 57% (4/7) a. Power brooming or street sweeper (one province used this for milled surfaces only) 0% (0/7) b. Air blowing or vacuum sweeper 14% (1/7) c. Both A and B 29% (2/7) d. Other: required clean, but did not specify method 0% (0/7) e. Nothing 9. (Check all that apply.) Do your agency’s specifications and/or plan notes clearly state whether the application rate is for: 0% (0/7) a. residual asphalt 29% (2/7) b. undiluted emulsion 29% (2/7) c. diluted emulsion 14% (1/7) d. does not specifically state? 29% (2/7) e. multiple answers by same agency 10. Is dilution of an emulsified tack coat allowed? 57% (4/7) a. yes 43% (3/7) b. no 11. If dilution is allowed, where is it allowed? (Check all that apply.) 75% (3/4) a. at the asphalt supplier’s terminal? 25% (1/4) b. at the contractor’s storage tank? 50% (2/4) c. in the contractor’s distributor? 0% (0/4) d. in another location? (please specify)

Summary of Survey Results (Canada) 105 12. How is the dilution rate of an asphalt emulsion verified? (Check all that apply.) 0% (0/4) a. certification by the asphalt supplier 0% (0/4) b. certification by the contractor 50% (2/4) c. sample taken and tested from the contractor’s storage tank 25% (1/4) d. sample taken and tested from the distributor 0% (0/4) e. visual observation during the dilution process 25% (1/4) f. dilution rate is not verified 0% (0/4) g. other method, please specify – write in (required) _________________ 13. How often is the dilution rate verified? 0% (0/4) a. daily 0% (0/4) b. monthly 50% (2/4) c. by project 25% (1/4) d. never 25% (1/4) e. other, please specify – summary below: The entire quantity of tack coat used on a contract is divided into one to three lots for each specified application rate. The lot is divided into sublots, typically consisting of the quantity used to cover an area of 40,000 m2. 14. Does your agency specify when traffic is allowed on the applied tack coat surface? If so, when? 0% (0/7) a. before the emulsion breaks (color change from brown to black) 14% (1/7) b. after the emulsion breaks 14% (1/7) c. after the emulsion has set (all the water has evaporated from the emulsion) 0% (0/7) d. after a specific time delay (for example, 30 min) 43% (3/7) e. traffic not allowed on fresh tack between distributor and paver 29% (2/7) f. does not specify 15. Does your agency specify when the paver is allowed to place asphalt on an emulsified tack coat? If so, when? 0% (0/7) a. before the emulsion breaks (color change from brown to black) 43% (3/7) b. after the emulsion breaks 14% (1/7) c. after the emulsion has set (all the water has evaporated from the emulsion) 0% (0/7) d. after a specific time delay (for example, 30 min) 43% (3/7) e. does not specify 16. What is the maximum time tack coat can be exposed before it must be covered by asphalt? 29% (2/7) a. hours—one: 2 h or less; one: ½ day 43% (3/7) b. days—most common responses: tack must be covered the same day or the same work shift 29% (2/7) c. no limit—tack must be kept clean 17. What is the maximum distance the tack coat can be applied in front of the paver? 14% (1/7) a. enter distance in feet: 900 ft (only one response) 86% (6/7) b. no specification regarding maximum distance: no more than 2 h of paving can cover, what can be covered in 1/2 day, what can be covered in 1 day 0% (0/7) c. other 18. Which methods does your agency use to minimize/prevent pickup of tack coat materials? (Check all that apply.) 86% (6/7) a. tack coat must break (color change from brown to black) before any type of traffic can be placed on the tack coat