Advancements In Tack Coats 2011

Advancements in Tack Coats

January 2011

Tack or Bond Coat

• A light application of asphalt or asphalt emulsion used to promote the bond between an existing and a new hot mix asphalt layer.

• The goal is to bond subsequent hot mix layers in order to approach the strength of a single, monolithic layer.

• Inadequate bond strength at the interfaces can lead to slippage between the asphalt layers, which may cause shoving, cracking, and other premature pavement failures.

Traditional Tack Coats

Problems with traditional tack coats:• Traditional tack coats are often tracked away

from the intended application area.• Tracking is unsightly and results in less tack

available to achieve maximum bond strength.• Tack coat tracked into parking lots, driveways,

and adjacent areas is expensive to remove.• Tracking in intersections can create a liability

due to a loss of friction.

Traditional Tack Coat

Advancements in Tack Coats: Trackless Tack • “Trackless Tack” or NTSS-1HM is a

specially formulated emulsion for high performing, non-tracking tack coat applications.

• Applies like a traditional tack coat with conventional equipment.

• Allows for faster paving applications and improved overall pavement strength.

Trackless Tack

Benefits of Trackless Tack:• Ultra fast curing tack coat, often in 10

minutes or less• Non-tracking

– No loss of tack material to adjacent areas– Improved appearance and less cleaning of

driveways, parking lots, vehicles, and construction equipment

– Less inconvenience to the public and improved paving crew efficiency

Trackless Tack

Benefits of Trackless Tack (continued):

• Improved bond between pavement layers– Less shoving, cracking, and other failures

associated with inadequate bond– May reduce rutting 1

• Improved density measurements– More consistent air voids across the mat 2, 3

– Improved values reported at the unconfined edge due to less shoving

Performance:FDOT Testing on Bond Strength

• FDOT testing on core samples of HMA using RS-1(H) and NTSS-1HM.

• Cores were sheared apart to determine the interfacial shear strength.

• Trackless Tack showed 54% higher shear strength.

Performance:LTRC (NCHRP 9-40) 3, 4

• The Louisiana Transportation Research Center (LTRC) recently evaluated the performance of three commonly used tack coat materials— CRS-1, SS-1H, and NTSS-1HM “Trackless Tack.”

• The study was based on controlled field conditions on an existing asphalt surface at LADOTD’s Pavement Research Center followed by the application of a 3” hot mix asphalt overlay.

Performance:LTRC (NCHRP 9-40) 3, 4

• Tack coat applications were carefully controlled

• Core samples were obtained and evaluated for Interfacial Shear Strength (ISS) to determine the bonding of the various tack coat materials

• A laboratory shear tester (LISST) was used to conduct the testing

• An analysis of air voids was also completed to determine the effect of the different tack coat materials on HMA density

Performance:LTRC (NCHRP 9-40) 3

0 0.05 0.1 0.15 0.2

Residual Application Rate (gal/yd2)

Interfacial Shear Strength

CRS-1 SS-1H NTSS-1HM

Summary of ISS Results:• At all application rates, NTSS-1HM yielded

the highest bond strength• CRS-1, regardless of application rate,

never achieved the ISS associated with the lowest application of NTSS-1HM.

• Using an estimated monolithic mixture strength of 729 kPa, NTSS-1HM yielded nearly 60% of the maximum bond strength compared to only 38% with SS-1H, and less than 14% with CRS-1.

Maximum Interfacial Shear Strength

CRS-1 SS-1H NTSS-1HM Monolithic Mixture

Percentage of Monolithic StrengthCRS-1 13.4%SS-1H 37.5%NTSS-1HM 59.0%

Performance:Can Tack Coats reduce rutting?

1 Abadie, C., “Louisiana Bituminous Surface Preservation Program: Enabling Thin Overlays,” LAPA Annual Meeting, June 2009

0.031 0.062 0.155

Variation of HMA Air Voids

CRS-1 SS-1H NTSS-1HM

Analysis of Air Void Measurements:• The study also evaluated the in place air

voids of each HMA section with varying application rates of CRS-1, SS-1H, and NTSS-1HM.

• NTSS-1HM sections had the most consistent air void contents regardless of application rate.

• The data suggests that the increased bond strength with NTSS-1HM reduces movement at the HMA layer interface allowing for more efficient compaction.

• The study subsequently evaluated PG 64-22 asphalt binder as a tack coat

• PG 64-22 in Louisiana typically meets the same specification as PG 67-22

• The hot applied asphalt binder was also compared to CRS-1, SS-1H, and NTSS-1HM “Trackless Tack”

• PG 64-22 exhibited lower bond strength than NTSS-1HM at all application rates

0 0.05 0.1 0.15 0.2

Interfacial Shear Strength

CRS-1 PG 64-22 SS-1H NTSS-1HM

Performance: Low Temperature (LTRC) 5

• In conjunction with the NCHRP 9-40 study, LTRC also evaluated the bonding performance of two common tack coat materials at various temperatures– NTSS-1HM “Trackless Tack” = high modulus– CRS-1 = low modulus

• The study was performed to address that historical studies were only evaluated at ambient temperatures, 77 °F

Performance:Low Temperature (LTRC) 5

Performance Analysis: Low Temperature (LTRC) 5

• The data shows that low modulus materials, like CRS-1, possess much lower bonding performance at higher temperatures

• NTSS-1HM “Trackless Tack” possessed far better high temperature performance coupled with mostly equal or better low temperature bond strengths

Performance Analysis: Low Temperature (LTRC) 5

• The data shows that bond strength increases with decreasing temperature, as expected

• NTSS-1HM, however, maintains excellent bond strength even as low as -10 °C

• Considering most tack coat failures occur at high temperatures, the data explains why high modulus materials have consistently out performed low modulus tack coats in the field even in cooler climates and conditions

Trackless Tack

Typical Physical Properties

PARAMETER TEST METHOD MIN MAX

Saybolt Furol Viscosity, SFS @ 25 oC ASTM D88 20 400

Storage Stablility, 1 day, % ASTM D244 ---- 1

Settlement, 5 day, % ASTM D244 5

Residue by Distillation ASTM D244 50 ----

Oil Distillate, % ASTM D244 ---- 1

Sieve Test* ASTM D244 ---- 0.3

Tests on Residue

Penetration @ 25 oC ASTM D5 ---- 20

Softening Point (oC) ASTM D36 65 ----

Solubility, % ASTM D2042 97.5 ----

Original DSR @ 82 oC (G*/SIN d, 10 rad/sec) AASHTO T111 1 ----

* The Sieve result is tested for reporting purpose only, and it may be waived if no application problems are present in the field.

Advancements in Tack Coats for OGFC • Open Graded Friction Courses are very

popular mixes because of improved safety and reduced roadway noise

• The use of OGFC has been curtailed in some areas because of durability issues with these mixes

• Bonded Friction Courses using a high application rate of polymer modified tack coats can improve durability

Open Graded Friction Courses

Advantages• Reduced risk of

hydroplaning• Improved drainage• Improved visibility• Coarse surface for

improved friction values• Improved ride numbers• Reduced noise• Improved driver safety!

Disadvantages6

• Reduced durability• Raveling/Debonding of

OGFC layer• Stripping in OGFC and/or

underlying layers• Difficult snow and ice

removal

Way, G., “PCCAS AR Task Force Report,” September 22, 2007

I-35 San Antonio, TX

FM 1431 Travis County, TX

Dense Graded HMA Permeable Friction Course

Existing Surface PFC

Developments in OGFC

• Durability issues can be largely addressed by producing a Bonded Friction Course (BFC) with improved tack coat materials and processes

• Historically, the Novachip® process using a “Spray Paver” has been the most well known Bonded Friction Course system

Novachip® Spray Paver Process

• Developed by Colas in the late ‘80s in France• Substantial use in the US since the late ‘90s• Consists of an application of a thin, gap graded

HMA layer over a polymer modified tack coat • Uses a specialized “Spray Paver” machine to

apply a thick tack coat immediately before the gap graded layer is applied

• Uses a polymer modified tack coat—Novabond

Novabond Tack Coat Used in Spray Paver• The polymer modified emulsion wicks into the

new gap graded mix by displacement and water vaporization

• The thick application seals minor cracks in the existing surface layer and forms a strong bond

• The resulting membrane also seals the existing surface to prevent water intrusion

• CQS-1HP emulsion with a min. 60% residue• Typical application rate of 0.13 to 0.30 gal/yd2

The emulsion membrane “wicks up” around the HMA aggregates

The emulsion cures, bonding the mix & pavement

Existing Pavement

5/8” minimumdepth of mix

3/16”emulsion membrane depth

3/8” nominal aggregate

9-12 mmcoating on aggregates

www.dot.state.fl.us/.../Asphalt/BondedAsphaltConcreteFriction.ppt

Novachip® Spray Paver Estimated Cost = $800,000/paver

Developments in Bonded Friction Course• Bonded Friction Course applications using

the Novachip® system have performed well over the last 20 years

• However, the use and adoption has been slowed because of the high cost associated with the specialized “Spray Paver” required by the Novachip® process

Developments in Bonded Friction Course• Because of the increased cost, there has

been a need for a non-tracking, polymer modified tack coat material to avoid the use of the specialized spray paver

• The goal is to use existing paving equipment, and still apply a high application rate of polymer modified tack

Developments in Bonded Friction Course• Even with using a fast drying material, like

Trackless Tack, curing rates for such high application rates have been unsatisfactory

• Extended cure times would lead to unacceptable delays and/or tracking

• Developments led to a new hot-applied, polymer modified Trackless Tack material, UltraFuse Trackless Tack

UltraFuse Trackless TackNon-Tracking Hot Applied Polymerized Tack

• Applied with conventional distributors and paving equipment

• Fills cracks in the existing pavement and seals the surface

• Can be paved on immediately after application, in approximately 10 seconds

• The non-tracking surface liquefies during placement of the new OGFC surface

UltraFuse Trackless Tack Continued

• The liquefied polymer modified membrane wicks into the new OGFC layer by displacement forming a strong bond

• Polymer modified for improved flexibility and bond strength

• Application rate equals the residual asphalt associated with emulsion applications: 0.09 to 0.18 gal/yd2

UltraFuse Trackless Tack US 301 in Tampa, FL with FDOT

15 seconds after application

UltraFuse Trackless Tack US 301 in Tampa, FL with FDOT

Pavement Interface

NT HAP TackApproximately 1/4- 1/3 inch thick

NCAT Testing

• After the FDOT application on US 301 in Tampa, BEI contracted the National Center for Asphalt Technology (NCAT) to do further studies

• Three different tack coats were evaluated: CQS-1HP (generic Novabond), NTSS-1HM, and UltraFuse Trackless Tack

NCAT Testing(continued)

• The same residual asphalt application rates were chosen for each tack coat material:– 0.08, 0.13, and 0.18 gallons per square yard

• The goal was to determine the maximum interfacial shear strength obtained with each tack coat material

UltraFuse Trackless Tack for Bonded Friction Course• In September of 2010, ALDOT created a

special provision to use “PG Asphalt for Trackless Tack” with an OGFC mix on US 231 in Wetumpka, AL

• The application and paving was performed on September 28, 2010 in the right side northbound (0.15 gallons/yd2) and southbound lanes (0.18 gallons/yd2)

UltraFuse Trackless Tack ”PG Asphalt for Trackless Tack” from ALDOT Special Provision No. 08-0945 September 7, 2010

PARAMETER TEST METHOD MIN MAX

Rotational Viscosity @ 135 °C, cP

AASHTO T316 ---- 3000

Penetration @ 25 °C, dmm ASTM D5 ---- 30

Softening Point, °C ASTM D36 70 ----

Original DSR @ 82 °C, G*/sin(d), kPa

AASHTO T315 1.0 ----

UltraFuse Trackless Tack US 231 in Wetumpka, AL with ALDOT

UltraFuse Trackless Tack for Bonded Friction Course• Allows the agency and contractor to apply

a Bonded Friction Course with conventional paving equipment

• Eliminates the requirement and cost associated with the specialized Spray Paver

• Improves bond strength to increase the durability of OGFC mixes

References1. Abadie, C. “Louisiana Bituminous Surface Preservation Program: Enabling Thin

Overlays,” LAPA Convention, June 2009.

2. Cooper, S. and Mohammad, L. “Influence of Tack Coat Type on the Density of HMA Mixtures,” 2006 Pavement Performance Seminar, April 2006.

3. Mohammad, L., Bae, A., Elseifi, M., Button, J., and Scherocman, J. Interface Shear Strength Characteristics of Emulsified Tack Coats. Published and presented at the Association of Asphalt Paving Technologists Annual Meeting, Minneapolis, MN, March 16, 2009.

4. Mohammad, L., “NCHRP Project 9-40: Optimization of Tack Coat for HMA Placement—Research Update,” LAPA Convention, June 2009.

5. Bae, A., Mohammad, L., Elseifi, M., Button, J., Patel, N. “Effects of Temperature on the Interface Shear Strength of Emulsified Tack Coats and Its Relationship to Rheological Properties,” TRB Annual Meeting, Washington, DC, January 2010

6. Kandhall et. al, “Open Graded Friction Course: State of the Practice,” TRB Circular, December 1998.

7. Way, G., “PCCAS AR Task Force Report,” September 22, 2007.

8. www.dot.state.fl.us/.../Asphalt/BondedAsphaltConcreteFriction.ppt

Special Thanks

• FDOT and APAC on US 301 in Tampa• ALDOT and Wiregrass Construction on

US 231 in Wetumpka• NCAT—Dr. Nam Tran

Questions?

Advancements In Tack Coats 2011

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