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

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Presentation on theme: "How? Significant $aving$ for Federal, State and Municipal DOTs Infrared Thermography Revolutionizes Asphalt Paving."— Presentation transcript:

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

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

4 Kim Willoughby Pavement Structure Engineer Washington State Dept. of Transportation Prof. Joe Mahoney Professor of Civil & Environmental Engineering University of Washington Pavement Pioneers

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

6  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 Vibratory soil compactor The Basic Story Cold planer Sweeper Tack coat

7 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

8 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

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

10 Paver accepting HMA directly from truck. Paver Operation

11 Material Transfer Vehicle (Roadtec SB- 2500)

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

13 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.

14 Compactor – Hamm HD 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

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

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

17 Types of Damage Aggregate Segregation Raveling and Moisture Damage Fatigue Cracking

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

19 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

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

21  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. Damage Mechanism

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23 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

24 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%

25  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!)  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!) Effect on Service Life EXTRA CREDIT PROBLEM: Who pays to repair or reconstruct pavement that fails prematurely? EXTRA CREDIT PROBLEM: Who pays to repair or reconstruct pavement that fails prematurely?

26 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

27  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) 1999 Study Results

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

29 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

30 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.

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

32 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/ft 3 Δ density drop (mean – min.) = 3 lbs/ft 3 ► 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

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

34 Example: Failing Profile   T = 33 C o (59.4 F o )  Density Results Mean 2058 kg/m 3 Max 2138 kg/m 3 Min 1953 kg/m 3  Density Criteria Range 185 kg/m 3 Drop 105 kg/m 3 { kg/m 3 x = lbs/ft 3 } Approx. 5% air voids over min.

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

36 5908 Example: Passing Criteria   T = 3 C o (5 F o )  Density Results  Mean 2205 kg/m 3  Max 2247 kg/m 3  Min 2179 kg/m 3  Density Criteria  Range 69 kg/m 3  Drop 27 kg/m 3

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

38 Example: Aggressive Rolling   T = 30 C o (54 F o )  Density Results Mean 2436 kg/m 3 Max 2494 kg/m 3 Min 2387 kg/m 3  Density Criteria-- better than expected Range 107 kg/m 3 Drop 49 kg/m 3

39 2000 Study Results  Density criteria Range < 96 kg/m 3 (6 lbs/ft 3 ) Drop < 48 kg/m 3  Note the pass/fail pattern vs. ΔT

40 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.

41 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!

42 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!

43 TEST METHODS: Random Sampling  Random sampling procedure assumptions: 1.All mix is uniform (within specified tolerances and risks) within a lot 2.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

44 ► Typical WSDOT overlay – one lot – 400 Tons 3.7 meter (  10 ft) wide lane, 45 mm (  1 ¾ in.) thick, 890 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 EXAMPLE: Random Test 1/5 segment of an 890 meter-long QA lot. Note cyclic end-dump thermal anomalies (ovals) and required Random QA test (red dot).

45 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

46 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

47 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

48  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 Conclusions (continued)

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

50 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.


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