1. How? Infrared Thermography Revolutionizes Asphalt Paving
Significant $aving$ for Federal, State and Municipal DOTs

2. Infrared Thermography Revolutionizes
Asphalt Paving
Intro slide
Leonard Phillips, FLIR Systems Kim Willoughby, Washington State DOT Prof. Joe Mahoney, University of Washington

3. Pavement Pioneers
Kim Willoughby, P.E.
Washington State Department of Transportation
Pavement Structures Engineer
P.O. Box 47365
Olympia, WA
phone: (360)
fax: (360)
cell: (360)
Joe P. Mahoney
Professor of Civil and Environmental Engineering
University of Washington
Box
121 More Hall
Seattle WA 98195
Phone:
Fax:
Cell:
Kim Willoughby Pavement Structure Engineer Washington State Dept. of Transportation
Prof. Joe Mahoney Professor of Civil & Environmental Engineering University of Washington

4. Typical HMA Highway Structure
Direction of Travel
Direction of Travel
Shoulder
Shoulder
Surface Course (HMA)
HMA thickness ranges from 2 inches to over 12 inches.
Crushed Surfacing Base Course (CSBC).
Base Course
Subgrade
Existing Soil(s)

5. The Basic Story Subgrade Base — Milled pre-existing roadway
Vibratory soil compactor
Subgrade
Base —
Crushed Surfacing Base Course (CSBS)
Compacted unbound aggregate base (UAB)
6 to 16-inch “lifts”
Milled pre-existing roadway
Cold planer—mills surface
Sweeper—picks up debris
Distributor truck—applies tack coat
Cold planer
Sweeper
Tack coat

6. What is hot-mix asphalt (HMA)?
HMA BATCH PLANTS Large (above) Small, portable (below)
Mixture of asphalt binder and aggregate (stone)
Combined in a batch plant at ~ 330°F
Temperature monitored at plant
Higher temperature causes “asphalt drain-down”: liquefied asphalt washes off the aggregate
Lower temperatures can cause mix to be too stiff for compaction

7. HMA transport to the work site
Truck haulage
Cooling
Atmosphere
Truck bed contact
175°F (79°C) = “cessation temperature”
Cooler HMA is too stiff to be compacted – has higher air voids & lower density than adjacent, warmer HMA
Temperature differentials can lead to localized rapid wear
Bottom photos courtesy Gary Orlove, Infrared Training Center

8. Paver (Roadtec RP )
Tracked paver accepting HMA directly from truck.
Direction of travel is to the right.

9. Paver Operation
Paver accepting HMA directly from truck.

10. Material Transfer Vehicle (Roadtec SB-2500)

11. Material Transfer Vehicle – RoadTec SB-2500C
Stores and transfers HMA from truck to paver
Anti-segregation auger remixes materials
25-ton (22.7 MT) surge capacity
Outgoing HMA
Incoming HMA
Hopper
Paver
Auger
Paver
Dump truck
Direction of travel

12. More on MTVs Allow continuous in-line paving Reblend HMA
Defeat thermal segregation
Defeat aggregate segregation
Transfer HMA to paver while reblending
Can accept HMA from haul truck while moving OR
Can be equipped to pick up HMA from windrows dropped by belly dump trucks – and transfer it to a haul truck.

13. Compactor – Hamm HD 120 78-inch-wide, double-drum roller
Operating weight: 26,675 lbs.
Centrifugal forces: up to 38,700 lbs.
Vibration frequency range: 2,520 to 3,000 vibrations per minute
Roller constantly sprayed with water

14. Thermal effect of roller on HMA
Cooling water
Photo courtesy Gary Orlove, Infrared Training Center

15. The Problem Localized areas of coarse surface texture
Premature failure due to raveling, moisture damage, and fatigue cracking

16. Types of Damage Raveling and Moisture Damage Aggregate Segregation
Fatigue Cracking

17. Research Began in 1996…
Master’s thesis
University of Washington
Former road construction worker

18. 1998 WSDOT/UW Study Program
Collaboration: Washington State DOT and University of Washington
Four projects chosen to maximize the occurrence of temperature differentials – (1) early or (2) late season or night operations
FLIR PM280 used to identify temperature differentials in HMA “mat” after laydown & to sample loose mix from truck
In-place nuclear density testing performed on finished pavement in normal and cool test temperature areas
Tests: aggregate segregation, asphalt/aggregate segregation, and density differentials

19. FINDING: Cyclic pattern of temperature anomalies
Correlation with premature failures
End dumps

20. Damage Mechanism
HMA cools during transport below “cessation” temp: about 79°C (175°F)
When dumped directly into paver, cool “crust” is not sublimated.
Paver extrudes cool, stiff material that can’t be compacted.

22. 1998 Study Results
All 4 projects experienced temperature differentials
Differential measured vs. “normal” temperature areas
From 7–39 C° (13–70 F°) cooler
Mean of 21 C° (38 F°)
No significant aggregate segregation
Good rolling and paver practices can minimize compaction deficiencies

23. 1998 Study Results (cont.)
Temperature differentials correspond to low density areas
Air voids increased over “normal” temperature areas from 1.6 to 7.8% (average of 3.9%)
5 density readings taken per LOT (max 400 T of HMA  0.6 mile of 10-foot lane, 2 inches thick)
Values evaluated as average and standard deviation
What density is acceptable?
Target air void percentage is 7% (93% density)
Up to 9% air voids (91% density) can be acceptable
Long term WSDOT average density = 93.1%

24. John Q. You-Know-Who! Effect on Service Life
RULE OF THUMB: There is a 10% reduction in HMA pavement life for every 1% increase in air voids over 7%.
(NOTE: You’ll see this material again!)
John Q.
You-Know-Who!
EXTRA CREDIT PROBLEM: Who pays to repair or reconstruct pavement that fails prematurely?

25. 1999 Study Program
Determine temperature differentials with respect to different material transfer devices/vehicles, haul times, environmental conditions, and other equipment, etc.
36 projects studied throughout entire paving season
Infrared camera used to detect temperature differentials and locate test areas
In-place density testing performed (nuclear densitometer) on finished pavement in specified normal and cool temperature areas

26. 1999 Study Results Temperature differentials: 3–38 C° (5.4–68.4F°)
Localized air voids increase with:
Increasing temperature differentials (> 14 C° = 25 F°)
Increasing haul time
No remixing prior to placement
Localized air voids decrease with:
Remixing of the mix prior to placement (decrease in temperature differentials)
An increase in air and/or mix temperatures (more time to compact)

27. Anomaly Pattern During Laydown
ΔT = 30 C° (54 F°)
Note twinning of anomalies

28. Extent of Pavement Affected
Area affected per truckload
Width (across mat) can range from 1 meter up to the entire width of the mat
Length can range from 1 to 6 meters or more
Typical size of low-temperature area is approximately 1.2 meters by 3 meters
Frequently occurs along parallel tracks due to paver extrusion pattern

29. 1999 Study Results — MTV performance
The Material Transfer Vehicle (MTV) accepts HMA from the truck (left), remixes it, and offloads it into the paver (right), which is followed by a compactor. Shuttle Buggy shown below. Movement of the paving train is toward the left.

30. REMEMBER…
RULE OF THUMB: There is a 10% reduction in HMA pavement life for every 1% increase in air voids over 7%.

31. 2000 Study Program
Conduct infrared imaging of unconsolidated mat in 17 projects
Select longitudinal “density profile” locations for nuclear densitometry
“Differential” anomaly ΔT  25 F° (17 C°)
Δ density range = 6 lbs/ft3
Δ density drop (mean – min.) = 3 lbs/ft3
Procedure
Minimum 3 to 4 profiles per paving project (nuclear gauge)
Begin nuclear densitometer readings 10 feet behind anomaly
Take readings through differential area every 5 feet for 50 feet
Calculate density differences for each profile

32. Density Profile Testing: Example
Thermography-detected temperature differential area
Edge of pavement
5 ft
Anomaly Offset
3.7 m (12 ft)
Longitudinal profile line
Nuclear density tests
Anomaly = Differential
Test section = 50 ft

33. Example: Failing Profile
DT = 33 Co (59.4 Fo)
Density Results
Mean 2058 kg/m3
Max 2138 kg/m3
Min 1953 kg/m3
Density Criteria
Range 185 kg/m3
Drop 105 kg/m3
{ kg/m3 x = lbs/ft3 }
Approx. 5% air voids over min.

34. Roadway Condition -- Failed Profile
Only 1 year after construction
Premature wear in the mat surface from traffic

35. Example: Passing Criteria
DT = 3 Co (5 Fo)
Density Results
Mean 2205 kg/m3
Max 2247 kg/m3
Min 2179 kg/m3
Density Criteria
Range 69 kg/m3
Drop 27 kg/m3
5908

36. Roadway Condition – Passing Profile
Roadway condition 1 year after construction.
Surface shows no visible wear.

37. Example: Aggressive Rolling
DT = 30 Co (54 Fo)
Density Results
Mean 2436 kg/m3
Max 2494 kg/m3
Min 2387 kg/m3
Density Criteria--better than expected
Range 107 kg/m3
Drop 49 kg/m3

38. 2000 Study Results Density criteria Note the pass/fail pattern vs. ΔT
Range < 96 kg/m3 (6 lbs/ft3)
Drop < 48 kg/m3
Note the pass/fail pattern vs. ΔT

39. Summary of 1999–2000 Study Findings
Temperature and density differentials are a significant issue.
Approximately ½ of the projects (28 out of 53) studied regularly exhibited temperature differentials >14 C° (25 F°)
Differential densities resulting from cooler than desirable mix shorten pavement life.
When differential >14 C° (25 F°) air voids typically increase 2% or more.

40. Rule of Thumb and Implications
There is a 10% reduction in HMA pavement life for every 1% increase in air voids over 7%.
Therefore, when differential >14 C° (25 F°) and air voids increase 2%, pavement life may be reduced by approximately 20%.
Without an MTV and during cool ambient conditions and a long trucking trip from the batch plant, differentials can be MUCH larger than this!

41. TYPICAL SOLUTION: Reconstruction
U.S.: $32 billion in 2002 to build and maintain highways to meet growing traffic volumes and loads.
Low density areas fail prematurely due to raveling, cracking, and moisture damage
Failure can occur within one year of paving
Failure becomes a maintenance issue with potential safety implications…and costs!

42. TEST METHODS: Random Sampling
Random sampling procedure assumptions:
All mix is uniform (within specified tolerances and risks) within a lot
All mix within a lot has an equal chance to be compacted to a specified density
BUT: low-temperature “differential” areas are anomalies with different material properties
THEREFORE: Random sampling cannot assess the occurrence or severity of density differentials

43. EXAMPLE: Random Test Typical WSDOT overlay – one lot – 400 Tons
1/5 segment of an 890 meter-long QA lot. Note cyclic end-dump thermal anomalies (ovals) and required Random QA test (red dot).
Typical WSDOT overlay – one lot – 400 Tons
3.7 meter (10 ft) wide lane, 45 mm (1 ¾ in.) thick, meters ( 0.55 mile) long
Note anomalies
5 random QA density tests per lot required
Only one random test would be taken (dot) in section
10 out-of-spec areas/lane would be missed completely
Worst-case scenario: miss 50 out-of-spec locations per lot

44. Systematic Density Specification
WSDOT is implementing a specification to locate and test density differentials
Disincentive of 15% of the ACP unit price possible if density differentials are located
Performed on 10 projects in 2002
Performed on 10+ projects in 2003

45. Testing Procedure
Use handheld IR camera or temperature gun to locate temperature differentials
4 or more anomalously cool locations per lot will trigger pay disincentive based on these potential low-density areas
If the densities are less than the minimum allowable density or exceed density profile criteria, then the contractor is penalized

46. Conclusions
A tour of pavements in Washington State shows that density differentials are a significant problem
Research results
Temperature differentials lead to density differentials that reduce pavement life
Δ pavement life = f (density differentials)
Temperature differentials occur in a cyclic pattern
Random density testing alone does not capture the severity of density differentials

47. Conclusions (continued)
Density profiles taken through anomalous areas can be used to evaluate the effects of temperature differentials
WA State at this time allows the use of either:
A systematic density specification (one density test in a temperature differential area)
A density profile specification
Performance specification (based on density) was implemented in 2002 on 10 projects and has been used on 10+ projects in 2003

48. Photos courtesy Simon Howell, Alaska DOT
Other States
Alaska
California
Connecticut
Georgia
Kansas
Maryland
Massachusetts
Minnesota
Texas
Utah….
Photos courtesy Simon Howell, Alaska DOT

49. Click on Pavement Research for report and tech note.
Questions?
A full research report, tech note, and infrared imagebase can be found at the following website:
Click on Pavement Research for report and tech note.