2. 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.
3. 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.
7. 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.
10. 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
11. 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
12. 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.
13. 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.
14. 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
16. Performance:
LTRC (NCHRP 9-40) 3
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.
20. Performance:
LTRC (NCHRP 9-40) 3
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.
21. Performance:
LTRC (NCHRP 9-40) 4
• 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
23. 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
25. 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
26. 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
27. 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 , 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.
28. 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
29. Open Graded Friction Courses
Advantages Disadvantages6
• Reduced risk of • Reduced durability
hydroplaning • Raveling/Debonding of
• Improved drainage OGFC layer
• Improved visibility • Stripping in OGFC and/or
• Coarse surface for underlying layers
improved friction values • Difficult snow and ice
• Improved ride numbers removal
• Reduced noise
• Improved driver safety!
30. I-35 San Antonio, TX
Way, G., ―PCCAS AR Task Force Report,‖ September 22, 2007
31. FM 1431
Travis County, TX
Dense Graded HMA Permeable Friction Course
Way, G., ―PCCAS AR Task Force Report,‖ September 22, 2007
32. Existing Surface PFC
Way, G., ―PCCAS AR Task Force Report,‖ September 22, 2007
33. 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
34. 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
35. 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
36. Novachip® Spray Paver Process
The emulsion membrane “wicks up”
around the HMA aggregates
The emulsion cures,
5/8” minimum
bonding the mix & pavement
depth of mix
9-12 m
3/8” nominal coating on
aggregates
aggregate size
3/16”emulsion
membrane depth
Existing Pavement
www.dot.state.fl.us/.../Asphalt/BondedAsphaltConcreteFriction.ppt
37. Novachip® Spray Paver Process
www.dot.state.fl.us/.../Asphalt/BondedAsphaltConcreteFriction.ppt
38. Novachip® Spray Paver
Process
www.dot.state.fl.us/.../Asphalt/BondedAsphaltConcreteFriction.ppt
39. Novachip® Spray Paver
Process
www.dot.state.fl.us/.../Asphalt/BondedAsphaltConcreteFriction.ppt
41. 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
42. 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
43. 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
44. UltraFuse Trackless Tack
Non-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
45. 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
55. UltraFuse Trackless Tack
US 301 in Tampa, FL with FDOT
NT HAP Tack
Approximately 1/4- 1/3 inch thick
Pavement Interface
56. 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
57. 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
58.
59.
60.
61.
62. 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)
63. 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
AASHTO T316 ---- 3000
@ 135 °C, cP
Penetration @ 25 °C, dmm ASTM D5 ---- 30
Softening Point, °C ASTM D36 70 ----
Original DSR @ 82 °C,
AASHTO T315 1.0 ----
G*/sin( ), kPa
71. 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
72. References
1. 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
73. Special Thanks
• FDOT and APAC on US 301 in Tampa
• ALDOT and Wiregrass Construction on
US 231 in Wetumpka
• NCAT—Dr. Nam Tran
