NCHRP Synthesis Tack Coat Specifications, Materials, and Construction Practices

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1 NCHRP Synthesis Tack Coat Specifications, Materials, and Construction Practices Danny Gierhart, P.E. Dave Johnson, P.E. Principal Investigators

2 What Exactly Is a Synthesis? A report that assembles and disseminates information on a topic of current highway practice. Prepared by a consultant who has expertise in the topic area, with assistance provided by a technical panel.

3 Technical Panelists: Lyndi Blackburn - Alabama DOT Paul Burch - Arizona DOT Steve Brakeall - Maryland State Highway Admin. Jerry Peterson - Texas DOT Steve Hefel - Wisconsin DOT Louay Mohammad - Louisiana State University Jason Dietz - FHWA Morgan Kessler - FHWA Nelson Gibson - Transportation Research Board

4 Project Time Line Originally proposed by TRB Standing Committee AFK40 in January 2016 Submitted to TRB February 15, 2016 Selected by NCHRP Oversight Panel May 2016 Awarded to selected contractors September 2016 Survey & Responses January April U.S. States 7 Canadian Provinces Follow-up 1 st Draft Report May 19, 2017 Panel Comments and Meeting June 1, nd Draft Report July/August 2017 Final Report October 2017 Anticipated Publication Spring 2018

5 Sections of the Synthesis Introduction Literature Review Survey Results Case Examples Conclusions Appendices

questions Tack Coat Application 28 questions Tack Coat

6 Survey - excellent response rate 41 Questions Tack Coat Payment Specs 2 questions Tack Coat Materials 4 questions Tack Coat Application 28 questions Tack Coat Evaluation 7 questions 7 Provinces Agency Survey 50 States

7 Literature Review Importance of Tack Coats Tack Coat Definitions Tack Coat Specifications Tack Coat Materials/Products Tack Coat Construction Practices Testing and Acceptance of Tack Coats Literature Review

8 Importance of Tack Coats To promote the bond between pavement layers. To prevent slippage between pavement layers. Vital for structural performance of the pavement. All layers working together. Apply along all transverse and longitudinal vertical surfaces. 8

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13 Consequences of Poor Bonding Poor pavement performance Slippage cracks Shoving Early fatigue cracking Bottom up Top down Costly pavement repairs Repair of isolated area relatively inexpensive Removal and replacement of a portion or the entire pavement structure is very expensive Shorter than expected pavement life can be devastating for agency budgets

14 Pavement failure types cited by agencies as potentially caused by poor bond strength Slippage of the surface layer Delamination of pavement layer Fatigue cracking Top-down cracking Rutting of the pavement Other distress(es) Agency Survey 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

15 Distress from Poor Bonding Shoving surface core days later - significant slippage

16 Distress from Poor Bonding Early Fatigue - Interstate Pavement in Missouri Attributed to Bond Failure

17 How Does It Happen? compression Bonded HORIZONTAL MICROSTRAIN tension compression Unbonded HORIZONTAL MICROSTRAIN tension Courtesy of NCAT

18 Tack Coat Definitions Undiluted Emulsion - an emulsion which consists primarily of a paving grade asphalt binder, water, and an emulsifying agent. Diluted Emulsion - an emulsion with additional water added to it. The most common dilution rate is 1:1 (one part undiluted emulsion and one part additional water). Residual Asphalt - the remaining asphalt after an emulsion has set, typically percent of the undiluted emulsion. Tack Coat Break - the moment when water separates enough from the asphalt to show a color change from brown to black. Tack Coat Set - when all the water has evaporated, leaving only the residual asphalt. Some refer to this as completely broken. Literature Review

19 What s wrong (if anything) with the following specification regarding application rate?: Apply the tack coat at a rate of 0.05 gallons/yd 2 Literature Review

20 What difference does it make? If the example spec intended 0.05 gal/yd 2 of residual asphalt: Undiluted emulsion applied at 0.05 gal/yd 2 using an emulsion with 60% residual asphalt, leaves 0.03 gal/yd 2 on the roadway. 40% less than intended Literature Review

21 What difference does it make? If the example spec intended 0.05 gal/yd 2 of residual asphalt: Diluted Emulsion using the same emulsion diluted 1:1 with water and applied at 0.05 gal/yd 2 leaves gal/yd 2 on the roadway. 70% less than intended Literature Review

22 What difference does it make? If the example spec intended 0.05 gal/yd 2 of residual asphalt: To receive Residual Asphalt at 0.05 gal/yd 2 using an emulsion with 60% residual asphalt, the contractor would need to apply: gal/yd 2 of Original Emulsion or gal/yd 2 of 1:1 Diluted Emulsion Literature Review

23 Tack Coat Specifications discusses ways agencies have specified issues related to tack coats provides information about: methods of material acceptance how tack is paid for by agencies tack coat material dilution tack coat application rates Literature Review

Tack Coat Specifications Most agencies specify tack coat materials using the following AASHTO specifications, or some form of them: Asphalt Emulsions M 140 anionic emulsions M 208 cationic emulsions

24 Tack Coat Specifications Most agencies specify tack coat materials using the following AASHTO specifications, or some form of them: Asphalt Emulsions M 140 anionic emulsions M 208 cationic emulsions M 316 polymer-modified cationic emulsions Asphalt Cutbacks M 81 rapid curing M 82 medium curing Straight Binders M 320 Performance Graded Asphalt Binder M 332 Performance-Graded Asphalt Binder Using Multiple Stress Creep Recovery (MSCR) Test Literature Review

25 Percentage of Materials Used 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% 0.4% 79.4% 0.0% 20.2% Agency Survey

26 Top 5 Emulsions Used 1.CSS-1h (52%) 2.Non-standard* (48%) 3.SS-1h (46%) 4.SS-1 (36%) 5.CSS-1 (28%) * Non-standard means that a state has come up with its own nomenclature for an emulsion, outside those specified in AASHTO M 140 (Anionic Emulsions), M 208 (Cationic Emulsions), or M 316 (Polymer-Modified Cationic Emulsions) Examples: SS-1hp, CRS-2h, EBL Agency Survey

27 Top Reduced Tracking Emulsion Used 1. NTSS-1hm (24%) Others specified (all by less than 3% of the states) CBC-1H CBC-1HT EM-50-TT E-Tac NTCQS-HH NTCQS-1HM NTCRS-1HM NTCRS-1HSP NTHAP NTT PATT UltraFuse UltraTack Non-tracking tacks are designed to improve the pavement performance by avoiding the tracking problems associated with traditional tacks. This material is typically manufactured to harden quickly and adhere minimally to tires. When a hot lift of asphalt is subsequently placed over the tack, the hardened tack is reactivated by the heat, and bonds the new overlay with the existing surface. (Seo, 2016) Agency Survey

28 Material Acceptance Most agencies accept material using one or more of the following methods: Approved Source List specifies pre-approved products and sources typically maintained on the agency s web site Supplier Certification agency relies on supplier testing requires document certifying material meets agency specs Testing of Samples samples from supplier or field project verify product meets AASHTO specs, some agencies also verify performance via some form of bond strength test Literature Review

29 How is tack paid for? 34% 66% Individual Pay Item Incidental to Paving Why is this important? Little incentive for sufficient tack application if not a direct pay item Agency Survey

30 * How is tack measured for pay? By volume volume of undiluted of undiluted emulsion emulsion - 58% By mass mass of undiluted of undiluted emulsion emulsion - 36% By volume or or mass of of diluted emulsion By volume or mass of residual asphalt - By area (square area yards) (square - 6% (2/33) yards) 0% 10% 20% 30% 40% 50% 60% 70% * Some states pay by more than one method, so % s do not add up to 100 Agency Survey

31 Emulsion Storage and Handling emulsions are the most commonly-used materials for tack coats care needs to be taken to make sure material doesn t separate insulated storage tanks gentle agitation proper temperature range avoid contamination consult supplier for compatibility information Literature Review

32 Tack Coat Construction Practices provides detailed findings on agencies and contractors best practices regarding the application of tack coat in the construction phase discusses: training and communication tack coat application rates dilution issues surface preparation application best practices asphalt distributors vehicle tracking of tack coat Literature Review

33 Examples of Agency Guidelines NC DOT 2012 available online 20 pages CalTrans 2009 available online 42 pages Many other examples exist Literature Review

Application Rate Guidelines Surface Type New Asphalt Mixture Old Asphalt Mixture Milled Asphalt Mixture Portland Cement Concrete NCHRP Report 712, Table 31 Residual Application Rate (gsy) Approximate

34 Application Rate Guidelines Surface Type New Asphalt Mixture Old Asphalt Mixture Milled Asphalt Mixture Portland Cement Concrete NCHRP Report 712, Table 31 Residual Application Rate (gsy) Approximate Rate Undiluted* (gsy) Approximate Rate Diluted 1:1* (gsy) * NCHRP Report 712, Table 31, includes residual application rates only. Values in italics were supplied using an example emulsion with 60% residual asphalt binder for comparison purposes only. Literature Review

35 What are avg. application rates? Agency Survey

36 APP. RATE SPECIFIED BY: How is application rate specified? 50% 40% 30% 20% 10% 0% Agency Survey

37 Dilution: Pros and Cons Agencies in the U.S. are fairly evenly split regarding whether or not dilution is allowed Dilution Pros larger liquid volume allows easier flow larger liquid volume allows easier overlap of fans Dilution Cons risk of losing control of the product requires additional time to break increased risk of tack flowing off roadway surface * The FHWA/Asphalt Institute Tack Coat Workshop recommended that emulsions used for tack coat should not be diluted. Literature Review

38 Is Dilution of Emulsified Tack Allowed? Dilution Recommendations 52% 48% Verify dilution amount Dilution cannot be used to stretch tack Residual value is key Dilution Allowed 48% (24/50) Dilution Not Allowed 52% (26/50) Agency Survey

39 Where is Dilution Allowed? 90% 80% 70% Asphalt Institute recommends that any allowable dilution occur at the supplier s terminal 60% 50% 40% 86% 30% 20% 33% 48% 10% 0% At the asphalt supplier s terminal At the contractor s storage tank In the contractor s distributor

40 Dilution verification method(s) allowed? 60% 50% 40% 30% 20% 10% 0% certification by asphalt supplier Agency Survey certification sample from by contractor contractor s storage tank sample from distributor visual observation during dilution process dilution rate not verified

41 Surface Preparation for Tack Why is a clean surface Important? Literature Review

42 Surface Preparation for Tack Power brooming is the most commonly-used method of cleaning the roadway surface Literature Review

43 Surface Cleaning Methods Power Brooming: 41% (25/57) 33% 2% 24% 41% Both Brooming and Air Blowing or Vacuum: 25% (15/57) Any of Multiple Specified Methods: 2% (1/57) Clean, but Method not Specified: 33% (20/57) Agency Survey

44 Clean, But Must Surface Be Dry? Literature Review found various viewpoints The goal of surface preparation is to produce a clean, dry surface. (FHWA Tack Coat Tech Brief, 2016) A small amount of moisture on the pavement surface should not be detrimental to long-term tack coat performance, although a damp pavement will slow the cure and break time of the tack coat emulsion. (NAPA s QIP 128 Best Practices for Emulsion Tack Coats, 2013) NCHRP Report 712 determined that for the effect of water on tacked surfaces in the majority of cases, there was no statistically significant difference between wet and dry conditions Literature Review

45 Application Temperatures Type and Grade RS-1, SS-1, SS-1h, CRS-1, CSS-1, CSS-1h Spraying Temperature, F Storage Temperature, F RS-2, CRS Non-Tracking Tack Polymer-Modified Emulsion (NAPA s QIP 128 Best Practices for Emulsion Tack Coats, 2013) Literature Review

46 GOAL: Complete, Uniform Coverage

47 GOAL: Complete, Uniform Coverage May & King: 10% bond loss = 50% less fatigue life Roffe & Chaignon No bond = 60% loss of life Brown & Brunton No Bond = 75% loss of life 30% bond loss = 70% loss of life Loss of Life 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% 0% 50% 100% Bond Loss Literature Review

48 Change in agencies self estimate of tack coat coverage Agencies Self- Estimate of Tack Coat Coverage 100% 90%-100% 70% - 90% 50%-70% < 50% 2012 Survey Results -NCHRP Report Survey Results NCHRP Synthesis 37% 11% (6/57) 27% 39% (22/57) 18% 39% (22/57) 9% 12% (7/57) 9% 0% (0/57) Agency Survey

49 Reasons for Non-Uniform Coverage Clogged Nozzles Literature Review

50 Reasons for Non-Uniform Coverage Incorrect Nozzle Type / Size Literature Review

51 Reasons for Non-Uniform Coverage Incorrect Nozzle Orientation Literature Review

52 Reasons for Non-Uniform Coverage Lack of Proper Pressure in Distributor Spray Bar Literature Review

53 Reasons for Non-Uniform Coverage Incorrect Spray Bar Height Literature Review

54 Reasons for Non-Uniform Coverage Using a Spray Wand in Areas Where Distributor Could Be Used Literature Review

55 Spray Requirements for Distributors none other uniform nozzles clean nozzles max. angle nozzle angle relative to the min. angle nozzle angle relative to the maximum height of the spraybar minimum height of the spraybar triple overlap of the emulsion streams double overlap of the emulsion streams spray without overlap of emulsion streams 0% 10% 20% 30% 40% 50% Agency Survey

56 Distributor Calibration-How often? Agency Survey

57 Distributor Calibration-Method? Agency Survey

58 Who performs the calibration? The contractor - 44% (14/32) The agency - 28% (9/32) Independent testing firm - 16% (5/32) Distributor manufacturer - 16% (5/32) Other - 3% (1/32) Agency Survey 0% 10% 20% 30% 40% 50%

59 When is traffic allowed on tack coat? before the emulsion breaks after the emulsion breaks after the emulsion has set after a specific time delay traffic not allowed on fresh tack between distributor and paver does not specify Agency Survey 0% 10% 20% 30% 40% 50%

60 Tracking of Tack Coat Literature Review

Methods Used to Minimize Tracking tack coat must break tack coat must set requires the use of reduced-tracking tack materials allows the use of reduced-tracking tack materials requires the use of

61 Methods Used to Minimize Tracking tack coat must break tack coat must set requires the use of reduced-tracking tack materials allows the use of reduced-tracking tack materials requires the use of spray pavers allows the use of spray pavers sanding of tack coat materials after application allows wetting/dampening of pavement before other method tracking or pickup continues to be a problem Agency Survey 0% 20% 40% 60% 80% 100%

62 Spray Examples Paver of Illustrations spray pavers Literature Review 62

63 Spray Paver Pros and Cons PROS No time for dust and debris to settle on tack coat surface No tracking of the tack CONS Lack of time for tack to break properly Must rely on proper maintenance and calibration because spray pattern difficult to see Literature Review 63

64 Are spray pavers allowed? Spray Pavers Allowed Spray Pavers Not Allowed Agency Survey

65 Are different tack materials used with spray pavers? 43% 57% Agency Survey different tack coat material used (16/28) same tack coat material used (12/28)

66 Different materials specified for use with spray pavers by number of states specifying polymer modified emulsion PG non-tracking tack Emulsion Bonding Liquid (EBL) CSS-1h CSS-1 polymer modified CRS-1s CRS-1P CQS-1hp Agency Survey

67 Testing and Acceptance of Tack Coats acceptance of tack coat material approved source list supplier certification of the product acceptance testing of field samples on a project basis acceptance testing of supplier samples on a material type basis Literature Review

68 Testing and Acceptance of Tack Coats acceptance of the in-place tack coat application assessment of tack coat coverage determination by volume determination by weight or mass determination by direct measurement, e.g. ASTM D2995 Literature Review

69 Example of Agency Field Verification Literature Review

70 Testing and Acceptance of Tack Coats acceptance by laboratory or field bond strength laboratory testing used for product approval field testing used to assess quality of field application common methods of load application tension, shear, torsion destructive vs. nondestructive cyclic vs. monotonic Literature Review

71 Examples of Bond Strength Tests Louisiana Interlayer Shear Strength Tester (LISST) Literature Review Interface Shear Load (kn) a P ult Displacement (mm) Courtesy of Dr. Louay Mohammad

72 Examples of Bond Strength Tests NCAT Shear Testing Device Literature Review Virginia Shear Tester

73 Examples of Bond Strength Tests Torque Bond Test Literature Review

74 Examples of Bond Strength Tests Kansas Tension Tester Virginia Tension Test Literature Review

75 Examples of Bond Strength Tests Texas Tack Coat Pull Off Device Literature Review

76 Bond Strength Testing? 11 (23%) 9 out of 14 (64%) SEAUPG states conduct some type of bond strength testing 36 (77%) Yes No Testing style? field tension testing lab tension testing field torsion testing lab torsion testing lab shear testing Agency Survey

77 When does your agency perform interface bond testing? On every project Agency Survey By special provision For product evaluation As part of forensic investigations Other

78 SHEAR TENSION Minimum Bond Strength Requirements? 30 PSI 1 35 PSI 40 PSI 50 PSI 70 PSI PSI 5 Agency Survey

79 Case Examples presents the results of in-depth communication with three states (KS, TX, WV) which were identified as candidates for further study information is presented regarding: their histories with interface bond testing a summary of their testing methods discussion of how the implementation of additional focus on tack coats has progressed and been received in their state. Case Examples

80 Appendices Survey Questions Summary of Survey Results Tack Coat Training Manual From NCHRP Report 712 Kansas DOT Bond Strength Specs and Best Management Checklists Louisiana DOTD Tack Coat Inspector Checklists

81 Areas of Known Agreement Layer Bonding is Vital Surface Preparation Clean Milling Improves Field Performance Shear Cleaning 81

82 Areas of Known Agreement Application Quality Vital Proper Rate Uniformity Distributor Truck Setup Calibration/Verification Maintenance Tacking of Longitudinal Joints Bonding 82

83 Areas of Known Agreement Tack Coat Rate Depends on Surface Condition Fresh Weathered Raveled Milled Need for Research Reduced Tracking Material Stability Long Term Performance 83

84 Questions?

Talking Tack: A Synthesis of Practices Around the U.S.

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