1. Considerations FOR more durable hma pavements
Ryan Barborak, P.E.
Texas Department of Transportation

2. Bonding 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 Demonstration
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:

4. Bonding 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:

5. Tack, Bond, Seal Conventional Tack Spray Paver
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?

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

7. Interlayer Material Guide

16. Thermal Segregation
Thermal segregation is defined as temperature differences in the hot mix asphalt (HMA) mat as it is placed. It is a potential cause of premature failure in asphalt roads. It can cause a significant reduction in pavement life due to low density from cold spots in the HMA mat.

17. Rules of Thumb – Why Does it Matter
For dense graded HMA, 1% increase in air voids (above a baseline value of 7%) will result in a minimum 10% decrease in pavement life
25°F temperature differential = 1-2% more air voids
No signification compaction occurs below cessation temperature (about 175°F).

18. Thermal Camera Examples of Thermal Segregation

19. Minimizing Hand Work

20. Thank You
QUESTIONS