How?

Significant $aving$ for Federal, State and Municipal DOTs

Infrared Thermography Revolutionizes Asphalt Paving

Leonard Phillips, FLIR Systems Kim Willoughby, Washington State DOT Prof. Joe Mahoney, University of Washington

Pavement Pioneers

Kim Willoughby

Pavement Structure Engineer Washington State Dept. of Transportation

Prof. Joe Mahoney

Professor of Civil & Environmental Engineering University of Washington

Typical HMA Highway Structure

Surface Course (HMA) Base Course Subgrade Existing Soil(s) HMA thickness ranges from 2 inches to over 12 inches.

Crushed Surfacing Base Course (CSBC).

The Basic Story

  

Subgrade Base —

• Crushed Surfacing Base Course (CSBS) • Compacted unbound aggregate base (UAB)  6 to 16 inch “lifts”

Vibratory soil compactor Cold planer Milled pre-existing roadway

• Cold planer—mills surface • Sweeper—picks up debris • Distributor truck—applies tack coat

Sweeper Tack coat

What is hot-mix asphalt (HMA)?

  

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

HMA BATCH PLANTS Large (above)

Small, portable

(below)

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 Heat loss from truck body: 224.9°F 227.1°F 200 14.6°F 50 150 100 Bottom photos courtesy Gary Orlove, Infrared Training Center

Paver (Roadtec RP-185-10)

Tracked paver accepting HMA directly from truck. Direction of travel is to the right.

Paver Operation

Paver accepting HMA directly from truck.

Material Transfer Vehicle (Roadtec SB 2500)

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 Paver Auger Dump truck Direction of travel

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.

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

Thermal effect of roller on HMA

336.3°F

Cooling water

300 250 200 150 72.9°F Photo courtesy Gary Orlove, Infrared Training Center 100

The Problem



Localized areas of coarse surface texture



Premature failure due to raveling, moisture damage, and fatigue cracking

Types of Damage

Aggregate Segregation Raveling and Moisture Damage Fatigue Cracking

Research Began in 1996…

►

Master’s thesis

►

University of Washington

►

Former road construction worker

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

FINDING:

Cyclic pattern of temperature anomalies End dumps Correlation with premature failures

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.

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

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%



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!)

EXTRA CREDIT PROBLEM: Who pays to repair or reconstruct pavement that fails prematurely?



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

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)

Anomaly Pattern During Laydown

► ΔT = 30 C° (54 F°) ► Note twinning of anomalies

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

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.

Equipment No MTV Blaw-Knox MC-30 Paddles operating Paddles not operating Roadtec Shuttle Buggy Cedarapids MS-3 Windrow Elevator Cedarapids MS-2 Other Windrow Elevator CMI MTP-400 Windrow Elevator/MC-30 Number of Projects with Typical  T <14 o C >14 o C Total 0 3 3 0 10 1 13 9 4 1 1 9 8 4 4 1 1 5 3 2 0 0 9 11 11 2 18 1 1

REMEMBER…



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

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

Density Profile Testing: Example

Thermography-detected temperature differential area

Anomaly Offset Longitudinal profile line Edge of pavement 5 ft 3.7 m (12 ft)

Nuclear density tests

Anomaly = Differential

Example: Failing Profile

Approx. 5% air voids over min.

  

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 0.0623 = lbs/ft 3 } Contract 5677 Profile #1

2600 2500 2400 2300 2200 2100 2000 1900 0 2 4 Average 2058 6 8

Distance (m)

10 12 14

Roadway Condition -- Failed Profile

►

Only 1 year after construction

►

Premature wear in the mat surface from traffic

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

Contract 5908 Profile #1

2600 2500 2400 2300 2200 2100 2000 1900 0 5908 2 Average 2205 4 6 8

Distance (m)

10 12 14

Roadway Condition – Passing Profile

►

Roadway condition 1 year after construction.

►

Surface shows no visible wear.

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

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

Number of Profiles Failed both density criteria Passed both density criteria Failed only density range Failed only density drop Percent passing Percent failing  T > 14 o C 28 20 3 3 2 10.7

89.3

 T < 14 o C 41 4 33 2 2 80.5

19.5

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 .

Rule of Thumb and Implications



There is a 10% reduction for every 1% in HMA pavement life 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!

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!

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

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).

►

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

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

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

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

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

Other States

         

Alaska California Connecticut Georgia Kansas Maryland Massachusetts Minnesota Texas Utah….

Photos courtesy Simon Howell, Alaska DOT

Questions?



A full research report, tech note, and infrared imagebase can be found at the following website : http://www.wsdot.wa.gov/biz/mats/pavement

Click on

Pavement Research

for report and tech note

.