1. Shear Bond Strength Testing
Stacy L. Hilbrich, P.E.
Angel Brothers Enterprises, Ltd
Century asphalt, ltd

2. Bonding (From Ryan Barborak, P.E., TxDOT)
Bonding is critical for the performance of the pavement
Design assumes all layers are bonded
Bonding is achieved through the use of a tack coat
Keys to successful bonding include
Clean surface
Uniform tack coat application
Proper amount of tack coat
Residual asphalt

3. Bonding (from Ryan Barborak, P.E., TxDOT)
Studies have shown that:
10% bond loss reduces the fatigue life by 50%
30% bond loss reduces the life by 70%
No bond reduces the life by 60% to 75%
Distresses include alligator (fatigue cracking), shoving, potholes, and rutting
Failure may occur due to bonding even though mix design is acceptable
“When in doubt, tack” Asphalt Institute
Source:

4. Bonding Demonstration (From Ryan Barborak, P.E.)
11 sheets of plywood: ”x8”x11/32”
Span length 36”
Weight of Person ~60 lbs
Measured deflection over span
Unbounded
Fully bonded
21 times difference
2 5/8”
1/8”
Courtesy of Wayne Felix
Source:

5. How bonded are pavement layers?
Slippage cracks

6. How bonded are pavement layers?
Slippage
Core
Utah

7. How bonded are pavement layers (cont.)?
Premature pavement failure – within 1 year
Longitudinal cracking in the wheel path and rutting
Full slip between 2 x 3” layers was a contributing factor to early distress

8. How bonded are pavement layers (cont.)?
Coring of new layer is a routine QC/QA activity to verify in- place density/calibrate nuclear density gage
How often do cores break at the interface between layers?
De-bonding

9. Tack Tracking in Wheel Paths – Consider Less Tracking Tack

12. Underseals (From Ryan Barborak, P.E., TxDOT)
Too much rock, should definitely consider tack.

14. SS3084 and SS3085

15. Tack, Bond, Seal (From Ryan Barborak, P.E., TxDOT)
Conventional Tack
Tack only
Tracking Resistant Asphalt Interlayer (TRAIL)
Hot Applied Asphalt
Tack, bond, seal
Emulsified Asphalt
Tack, bond
Spray Paver
Tack, bond, seal
Underseal
Seal
Seal coat binders/aggregates
Apply just enough rock to keep binder from tracking
Should it be tacked?

16. TACK, BOND, SEAL Conv. Tack Underseal Spray Paver Hot-Applied TRAIL
Emulsion TRAIL
TACK
BOND
SEAL

17. TEX-249-F Shear Bond Strength Test

19. IS IT REPEATABLE?

20. DOES IT APPLY TO ALL MIX TYPES?
Open-graded mixes will have a lower tensile strength in general because there is less direct contact between the aggregate particles & have a higher air void content.
The test method require a minimum of 1.5” of each layer being tested. This will be a challenge in thin overlays.

21. Considerations for Bond Strength (From TTI Research Report 0-6908-P2)
Bond strength is influenced by:
Tack material type
Existing surface condition
Overlay type
Compaction temperature
Time after construction
Bond strengths tend to increase substantially within the first month.
Shear bond strengths could be low, but it is not necessarily an indication of poor performance.

22. What to do on Concrete?
MoDOT Specification for over 10 years requires the membrane be tested in the lab with a pull-off test.

23. Any questions?