Thermal Segregation. Wednesday, December 8, 2010 SEAUPG 2010 ANNUAL CONFERENCE OKLAHOMA CITY, OK. Acknowledgements. Thermal Segregation - Background

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1 Thermal Segregation 2010 SEAUPG Meeting Oklahoma City Acknowledgements Richard Izzo, P.E. - TxDOT Stephen Sebesta TTI Texas Transportation Institute (TTI) National Center for Asphalt Technology (NCAT) Moba Corporation Dale A Rand, P.E. Flexible Pavements Branch Construction Division. Thermal Segregation - Background Example of a Density Profile Historically segregation thought of as mechanical (gradation) phenomenon 1996 WSDOT discovered thermal imaging could detect segregation Cold spots became low density areas 89 percent of locations with t > 25 F failed density uniformity criteria Thermally segregated locations holding water (courtesy WSDOT) NCAT (2000) and TTI (2002) similarly found thermal uniformity suitable for detecting segregation NCAT low severity segregation when t > 18 F TTI when t > 25 F, TxDOT density uniformity requirements not met Change in Density (pcf) Spec max density differential = 6 pcf y = x R 2 = pcf density differential at ~ 25 F -10 temp differential Why is Thermal Segregation Important? Recall cold spots typically become low density Density is a or the primary contributor to pavement performance Contractor and agency risk are impacted Acceptance and pay schedules are based on density Segregated locations distress prematurely -15 Change in Temp (F) 1

2 How Thermal Segregation Impacts Performance Cold spots tend to be low density These locations hold water These locations often begin with a coarser texture and ravel Ultimately loss of fatigue life occurs Type D HMA. More compaction effort is necessary as temperature decreases. Thermally Segregated Not Thermally Segregated Early observations: coarser texture and holding water Source: NCAT (2000) 2

3 TxDOT Definition of Thermal Segregation Moderate Severe How TxDOT Specifications Addresses These Concerns A minimum of one Thermal Profile is required on every sublot of HMA. No QCQA bonus is paid if there is severe thermal segregation. A Density Profile is required a minimum of once on every sublot. And Every time the paver stops And at locations where thermal segregation is identified Contractor waives QCQA bonus if profile fails Remove and replace sublot if it fails the density profile and has severe thermal segregation. Common Methods of Measuring Thermal Segregation Infrared Thermometers less than $200 Infrared Cameras less than $5K Pave-IR System less than $30K Test Method Tex-244-F Handheld IR thermometer Thermal camera Pave-IR Press the button to view summary results Pave-IR Summary Results Screen 3

4 Example report from project with severe thermal segregation Test Device Strengths Weaknesses Handheld IR Thermometer IR Camera Pave-IR Inexpensive. Simple to use. Tests independent of paving train. Inexpensive. Simple to use. Tests independent of paving train. More coverage than thermometer. Does not require constant operator attendance. Provides real-time feedback. Tests virtually full-coverage. Automated data reduction. Permanent record. Requires constant operator attendance. May miss localized defects. No permanent record. Requires constant operator attendance. May miss localized defects. No permanent record (usually). Most costly device. Testing coverage could impact risk of finding defects. May include artificial cold spots in data set. 4

5 Conclusions Physical & thermal segregation are the Cancer of HMA Paving Industry You cannot always see it. It grows with time. It often results in the early death of the pavement - often the only reason some HMA pavement are in need of rehabilitation There are many known & suspected causes & cures No consensus Identifying & Eliminating Thermal Segregation is a Major Goal for TxDOT Conclusions TxDOT is implementing better specifications & better techniques to address the problem The Pave-IR System is an excellent Passive Inspection device that allows end result versus method specifications It allows contractors to see what they are doing and improve their operations Contractors can focus on causes & cures What Gets Measured Gets Done A segregated mat increases contractor s chances of QC/QA core location being in a poor/low density area A segregated mat increases agency s risk of early distress Eliminating segregation and placing uniform, high quality HMA is good for both contractor and agency 5

6 Background, Use, and Advanced Techniques Dale Rand (TxDOT) Richard Izzo (TxDOT) Stephen Sebesta (TTI) Truck-end Streaks Random Production temperature changes Paver stops Occurs at truck exchanges Can occur with any operation Typically most severe with end-dump straight into paver hopper Different texture is often (but not always) visually observed Occur at a specific transverse location, rather continuously, behind the screed Often caused by paver operational issues, or in some cases a pattern is inherent to a certain paver/operation Localized cold spots with no apparent pattern May be small clumps of mix; in some cases these are removed by paving crew Plant production temperatures may change throughout the day The transition will show in the thermal profile Truck-end and within-truck (random or streak) thermal segregation is more concerning

7 Cold spot, often followed by localized hot spot from paver burners Per Tex-244-F these sections are excluded from thermal profile analysis Test Method Tex-244-F Handheld IR thermometer Thermal camera Pave-IR Perform one test per sublot One test evaluates 150 feet of paving The outer 2 feet of the mat are not tested Locations of paver stops > 10 seconds are not included in the data Thermal profiling with handheld IR thermometer or thermal camera according to Test Method Tex-244-F Install to paver according to manufacturer instructions Initiate data collection Data are collected on all paving; not localized areas Generate automated report Temperature differential is determined for each 150-foot Test Device Strengths Weaknesses Handheld IR Thermometer IR Camera Pave-IR Inexpensive. Simple to use. Tests independent of paving train. Inexpensive. Simple to use. Tests independent of paving train. More coverage than thermometer. Does not require constant operator attendance. Provides real-time feedback. Tests virtually full-coverage. Automated data reduction. Requires constant operator attendance. May miss localized defects. Requires constant operator attendance. May miss localized defects. Most costly device. Testing coverage could impact risk of finding defects. May include artificial cold spots in data set. 7

8 In plot below, coldest spots are pockets Each pocket ~ 1 to 1.5 ft. long by ~ 2 ft wide The random and continuous scanning with IR thermometer may not detect these spots Using Pave-IR: Installation, Data Collection, and Data Reduction Video Demonstration Installed system collecting project data Select Create New Project from the main Choose Project/Project Overview screen Enter Project Properties 8

9 After inputting project properties, select Pave-IR returns to the main screen Select the desired project by touch screen then press Projects with the roadway icon do not have any data Projects with the flash drive icon contain data Thermal plot, position, distance, and speed are updated real-time Stationing (if used) will display on color plot Paver stop limits shown with horizontal red bar Note the stationing displayed over the thermal plot and the limits of two paver stops Press from the data collection screen, then when asked if you want to return to project overview If using stationing, the Adapt Sensor Location screen appears Adjust the test stop point, if necessary, to the stop point s stationing, then press This adjustment may be necessary if the odometer s rolling radius value contains error. Pave-IR returns to the main Choose Project screen 9

10 Restore location calculated by software Accept location Open the project s data log file in Pave Project Manager Select: Report \ Generate \ Tex-244-F Press Type desired entries into the input fields, then press Sensors ignored during data collection will also be ignored for generation of Tex-244-F report 1 2 Example report from project with minimal thermal segregation

11 The Nuts and Bolts of Thermal Profiling with Pave-IR TxDOT Spec: One profile per sublot Engineer may reduce testing frequency Engineer may also obtain as many thermal profiles as deemed necessary Tex-244-F profiled 150 feet of paving Essentially Pave-IR profiles each 150 foot segment of paving Automated data processing methods selected to mimic structure of existing Tex-244-F Remember the primary goal of testing Detect thermal signatures in the placement operation such as Truck Ends Streaks Random cold spots within truckloads Excludes the outer 2 feet toward the edges Determines maximum baseline temperature in first 20 feet of paving This temperature will generally not be the absolute maximum from within a profile s limits This approach reduces the contractor s risk Tex-244-F determines the minimum profile temperature over 150 feet Locations of paver stops > 10 sec. excluded from analysis Must ignore outer 2 feet toward edges Must mimic risk structure in terms of leniency on the maximum temperature Must ignore paver stops Must not produce false positives Must automatically process data Sensors to ignore selected prior to initiating data collection In most cases these are the outer 2 sensors on each side Pave-IR stores which sensors to ignore, and reports which sensors were not used in the temp. differential determination 11

12 Researchers manually evaluated 380 profile segments The hottest spot in the first 20 is typically 98.5% of the hottest spot in the entire profile segment Pave-IR ignores 1.5% of the hottest temperatures to determine the maximum baseline temperature Paver stop defined as > 10 seconds idle time Reviewed over 30 paver stops from 4 different projects Ignore 2 prior to stop Ignore 8 after stop Using this approach eliminated irregular thermal signatures attributable to the paver stops in all cases examined External factors could create artificial cold spots in data log files Hand work, cooler spills Artificial cold spot from hand work Red bars beneath profile are limits ignored due to paver stop. A single point approach for determining the minimum profile temperature would artificially inflate the temp. differential when these external factors are present in a profile Pave-IR ignores the coldest 1% of temperatures to determine the minimum profile temperature Operator selects which sensors are within 2 feet of edges. These sensors are ignored from calculations For each 150 foot segment Data 2 feet prior, and 8 feet after paver stops lasting > 10 seconds are ignored Omit hottest 1.5% of measurements to determine maximum baseline temperature Omit coldest 1% of measurements to determine minimum profile temperature Profile temp. differential = max - min 12

13 Pave Project Manager (PPM) allows for automated reporting and manual data review Opening a data file Changing the color map scale Viewing the thermal profile Scrolling through the profile Profile view options Ignored sensors and profile length Tooltip and spots of interest Properties, Time, Speed, and Temperature Class Diagrams Illustration with 2 project files Texas 15 Units Other users: Minnesota Wisconsin NCAT Other interested regions: Alaska Quebec Ohio Michigan Germany China Moba Corporation Paul Angerhofer (cell) p.angerhofer@moba.de Moba Corporation Gary Motak (cell) g.motak@moba.de Moba Corporation James Lano (cell) jlano@moba.de New Technology for Measuring Pavement Quality 11/

14 Method developed by Texas Transportation Institute to detect segregation in newly placed uncompacted asphalt Uses a series of infrared sensors mounted to screed Sensors are connected to a screed mounted computer with color display Computer displays data from sensors Segregation is displayed in real-time Data stored on flash drive for post processing on PC 1996 University of Washington Construction Related Temperature Differential Damage in Asphalt Pavements 2000 US Transportation Research Board, National Research Council Segregation in Hot-Mix Asphalt Pavements 2002 Texas A&M University, Texas Transportation Institute Using Infrared Imaging and Ground-Penetrating Radar to Detect Segregation in Hot-Mix Overlays 2005 Texas A&M Universtiy, Texas Transportation Institute New Infared Imaging and Radar Systems for Detecting Segregation in HMA Overlays 2005 Colorado Department of Transportation Research Branch Thermal Segregation 2006 Clemson University Labratory and Field Investigation of Temperature Differential in HMA Mixtures Using an Infrared Camera Provides real-time thermal image of newly placed mat Logs and displays temperature segregation Complete job profile can be examined and areas where segregation is identified are easily located with GPS coordinates Allows contractor to quickly identify poor quality and apply corrective actions where needed Data can be viewed later on office PC and examined for areas where premature failure are possible Truck End Segregation Improper Loading of Haul Trucks Too Long of Haul Time Improper use of Tarps Wing Dumps Dumping Paver Wings After Each Truckload Cold Streaks Inconsistent Screed Temperature Cold Joints Cold Spots 14

15 Ensures compliance with most existing DOT temperature measurement requirements Easy to use Data is logged automatically and can be stored permanently More cost effective than infrared cameras Integrated GPS System records paving speed and paver stops System can be easily moved from one machine to another System is scaleable from 2-8 meters depending on paving width INFRARED SENSOR SIGNAL CONDITIONER MOUNTING HARDWARE DISTANCE ENCODER GPS ANTENNA PAVE-IR COMPUTER Operator Creates New Project File Project ID Operator Name Starting Location or Station Roadway ID HMA Type Sample Rate Lift Number Paving Width Lift Thickness Minimum and Maximum Temperature Range Comments Operator Starts Data Collection Microsoft Windows CE Operating System 6.5 Inch TFT Color Display 2GB Internal Memory 2GB USB Flash M D i 15

16 PC Software Used to View Saved Project Files Displays All Project Data Thermal Profile Temperature Histogram Paving Speed Data Paver Stops GPS Location Approximately 65 Foot Pull (Intersection) 12 Foot Paving Width 2 Inch Lift Ambient Temperature 58 Degrees F 16

17 PAVER STOP MANHOLE PAVER STOP PAVING SPEED Approximately 60 Foot Pull (Intersection) SCREED HEAT DURING STOP 12 Foot Paving Width MANHOLE 2 Inch Lift TEMPERATURE HISTOGRAM Ambient Temperature 60 Degrees F 17

18 Over 3 Construction Seasons Thermal Imaging was conducted on 40 paving projects At Time of Construction Infrared camera was used to take thermal images of pavement at truck changes GPS was used to document location where image was taken Took limited density measurements with nuclear density gauge TRUCK END SEGREGATION Occur with virtually every truck change Are located approximately feet from screed stop TEMPERATURE Δ = 60 DEGREES F TEMPERATURE Δ = 76 DEGREES F TEMPERATURE Δ = 80 DEGREES F 18

19 Of The 40 Projects Two Have Stood Out Route 44 Constructed in 2001 Average Temperature Δ 52.1 Degrees F Route 7 Constructed in 2002 Average Temperature Δ 34.5 Degrees F Route 44 and Route 7 One Significant Difference Both were produced with same HMA plant Were essentially the same paving crews/equipment Both were placed July/August timeframe Both had approximately 30 haul units/day Haul time one way by far the longest Route 44 Approx. 85 min Route 7 Approx. 110 min Route 44 End dump into paver hopper Route 7 Material Transfer Vehicle Non-remixing ROUTE 44 The following images were taken on Note the surface distress. These were areas that were observed to have cold spots when viewed with the thermal camera during paving just a few years ago. Wide variation in surface texture throughout project Cores from the worst surface texture areas had average air voids content = 13.8% Cores took over a month to dry on countertop Cores cut from areas with less texture had an average air void content = 4.1% 19

20 Route 44 Road Surface Has Required Patching Route 44 Same Location - Opposite Direction Route 44 Salt Creeping Out of Voids Va=17.2% Route 44 Core 20

21 Route 44 Raveling Route 7 Surface texture throughout project is generally uniform Cores cut from the worst surface textured areas had average air voids = 8.2% Cores cut from the more typical surface texture had an average air content = 5.4% Route 7 3 Years After Paving Route 7 3 Years After Paving CONCLUSIONS A MTV should be considered when hauling excessive distances even during warm weather. It is very difficult to differentiate between gradation and thermal segregation just by looking at the pavement. Thermal segregation does appear to shorten pavement s surface life. FINAL CONSIDERATIONS PAVE-IR does not prevent segregation Temperature segregation does not always equal material segregation Material segregation DOES equal temperature segregation PAVE-IR was developed by TXDOT and Federal Highway sponsored research Many state DOT s and the Federal Highway Administration continue to research how temperature segregation relates to premature failure of HMA pavements. Segregation can be prevented! 21

22 CONTACT INFORMATION JAMES LANO MOBA CORPORATION 180 WALTER WAY #102 FAYETTEVILLE, GA (678) PAVE-IR COMPONENTS Developed by Texas Transportation Institute with TxDOT research funds to detect Thermal Segregation in newly placed un compacted asphalt Uses a series of infrared sensors mounted to back of paver Sensors are connected to a computer with color display Computer displays data from sensors Thermal Segregation is displayed in real time Data stored on flash drive for post processing on computer INFRARED SENSOR SIGNAL CONDITIONER MOUNTING HARDWARE DISTANCE ENCODER GPS ANTENNA PAVE-IR COMPUTER (OPERAND) IR Bar Support Arm Infrared Sensor Upright Support Arm Protective Tube Base Plate 22

23 Folding Point Distance Encoder Attached to Hub Calibrate Distance Encoder Daily Looking From Tractor PAVE-IR Computer aka Operand MOBA PAVE-IR COMPUTER Right IR Bar Microsoft Windows CE Operating System 6.5 Inch TFT Color Display 2GB Internal Memory 2GB USB Flash Memory Drive Enough Memory for 25 Lane Miles Touch Screen 23

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25 0 50 ft ft ft. Full Screen View Summary Data 25

26 DATA COLLECTION SCREEN The Pave IR is allowed by SP At the option of the Contractor for personal Quality Control (to monitor and improve operations), or for official QC/QA (thermal segregation testing) Personal QC Only (not used for compliance) business as usual all requirements in and Tex 244-F still apply Official QC/QA segregation profiles are performed continuously by the system Thermal segregation definition changes Changes when using the Pave IR System Paving temperatures Thermal profiles Segregation (density profiles) Table 10A Minimum Pavement Surface Temperatures Moderate Minimum Pavement Surface Temperatures in Degrees Fahrenheit Originally Specified High Temperature Binder Grade Subsurface Layers or Night Paving Operations Surface Layers Placed in Daylight Operations PG 64 or lower Severe PG PG 76 or higher Contractors may pave at temperatures 10 F lower than the values shown in Table 10A when utilizing a paving process including WMA or equipment that eliminates thermal segregation. In such cases, the contractor must use either a hand held thermal camera or a hand held infrared thermometer operated in accordance with Tex-244-F to demonstrate to the satisfaction of the Engineer that the uncompacted mat has no more than 10 F of thermal segregation. 26

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28 Must ignore outer 2 feet toward edges Must mimic risk structure in terms of leniency on the maximum temperature Must ignore paver stops Must not produce false positives Must automatically process data 28