Implementation of the Pave-IR System in Texas Russel Lenz, P.E. TxDOT Construction Division Division Director Virginia Beach August 3, 2011

Background Historically, segregation (both physical & thermal) has been a major contributor to premature failures in flexible pavements with HMA surfaces. TxDOT’s 2004 Standard Specifications attempted to address these concerns by requiring thermal and density profiles and by restricting paving when the surface temperature is below 60°F (70°F for SMA - 50°F for unmodified binders). Many TxDOT districts also required the use of MTVs (shuttle buggies) to mitigate the problem. Method of measuring thermal segregation with a hand held infrared thermometer proved to be relatively ineffective. For the past 10 years, TxDOT has been working with TTI to develop a better methodology to measure thermal segregation. TxDOT is now implementing the Pave-IR system developed by TTI and manufactured by Moba Corp.

TxDOT Definition of Thermal Segregation Moderate Severe >25°F to 50°F >50°F ©2010 Hot Mix Asphalt Center - All Rights Reserved

Pave-IR Output Showing Thermal Segregation (Truck End) 220 314 316 220 320 314 240 215 310

How TxDOT Specifications Address Segregation A minimum of one “Thermal Profile” is required on every sublot of HMA. (Thermal profiles are 150 ft. in length.) A “failing” thermal profile requires an additional density profile. Failing is defined as > 25°F thermal segregation. No QC/QA bonus is paid if there is “severe” thermal segregation. A “Density Profile” is required a minimum of once on every sublot. (11 density gauge readings taken 5 ft. apart in a line parallel to paving direction) And every time the paver stops And at locations where thermal segregation is identified And where visible segregation is identified Contractor waives QC/QA bonus if profile fails Remove and replace sublot if it fails the density profile and has severe thermal segregation. Note: density profiles are never required and are not applicable if the Contractor opts to use the Pave-IR system.

Implementation of the Pave-IR System Goal: Improved pavement performance by encouraging Contractors to improve paving operations Optional for use on TxDOT HMA paving projects TxDOT specifications incentives No density or thermal profiles Opportunity to pave at lower temperatures (down to 32°F if dry) Potential QCQA bonuses not waived for non compliance to density profile or thermal segregation requirement

Implementation of the Pave-IR System TxDOT specifications incentives (cont’d) Used in lieu of an MTD – End dumps not allowed w/o MTD Automated documentation Contractor’s ticket taker not required to measure mix temperature and record station # on haul tickets Other minor incentives included in specification

Thermally segregated locations holding water . Thermal Segregation - Background 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 Thermal segregation work began as agencies were becoming more concerned with uniformity and paver stops. The density differential test was one outcome of agencies trying to obtain more uniform pavements and reduce the amount of paver stops. Thermally segregated locations holding water (courtesy WSDOT) 8

Example of a Density Profile (in pcf) Note: TxDOT allows a maximum differential of 6 pcf from high to low or 3 pcf from low to average. Research conducted by University of Connecticut, Connecticut Advanced Pavement Laboratory

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 10

Why is Thermal Segregation Important? Cold spots typically indicate low density areas 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 Ride quality ultimately impacted by thermal segregation

Early observations: coarser texture and holding water Common Performance Problems Early observations: coarser texture and holding water

Raveling and Cracking Follow

Fatigue Life Substantially Reduced Even moderate (>25 but < 50 F) thermal segregation can result in substantially reduced pavement life. Source: NCAT (2000) 14

Common Methods of Measuring Thermal Segregation Infrared Thermometers – less than $200 Infrared Cameras – less than $5K Pave-IR System – less than $30K

Measuring Thermal Segregation Test Method Tex-244-F Handheld IR thermometer Thermal camera Pave-IR

Current Usage of Pave-IR Texas – 25+ Units Other users: Minnesota Wisconsin NCAT Other interested regions: Washington Alaska Quebec Ohio Michigan Germany China As of September 2010 these are the current users, and agencies/regions that have expressed interest in demonstrations 17

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

Pave-IR Summary Results Screen Summary Results during Data Collection Press the button to view summary results **Emphasize how to interpret this screen, what is important for inspector, and how to interpret the status bars… The summary results first shows thermal segregation results for all profiles collected thus far in the data file. The top half of the results table presents these results. Each 150’ segment is analyzed to determine its temperature differential, then the results are summarized according to the number and percent of profiles containing moderate and severe thermal segregation. The categories are color-coded green, yellow, and red for no, moderate, and severe thermal segregation, respectively, and this status bar is color-coded according to the percentages in each category. The lower half of the table defaults to present the result from the most recent profile. However, using the cursor buttons, the user may scroll through each individual profile to review the individual temperature differentials. Selecting to view the Results Summary Options will display which sensors are ignored from the analysis. Data collection continues as normal while reviewing summary results. Touching the checkmark will return to the data collection screen. Pave-IR Summary Results Screen 19

Example report from project with minimal thermal segregation The color plot shows ~ 750 feet of paving, with minimal thermal variations. The report contains project information, a summary of the segment length, threshold temperature differential, and which sensors were ignored, then a thermal profile summary all on the first page. Subsequent report pages present summaries of locations with and without thermal segregation, a cumulative frequency distribution of measured placement temperatures, and locations of paver stops greater than one minute. ** Emphasize what is important for inspector – 0 “severe” and a nominal percentage “moderate” is good 20

Note report pages 3 & 4 are just continuations of profiles without thermal segregation 21

Example report from project with severe thermal segregation

Next Slide All circumstances require NO reporting of test results (or when Pave-IR is used for informational only) Use of Pave-IR YES Measure temperature of HMA & document with Station # on each haul ticket Next Slide Comply with pavement surface temperature requirements Perform density profiles Paver stops Thermal segregation Visibly segregated areas 1 per sublot Perform Thermal profiles 1 per sublot Handheld thermometer Thermal camera Pass Fail Temperature differential < 25ºF Moderate thermal segregation Thermal differential 25 - 50°F Severe thermal segregation Thermal differential > 50°F When Moderate Thermal Segregation (25°F – 50°F) is Detected If Contractor uses hand held thermometer or thermal camera for specification compliance: Take corrective action and: Perform a density profile at the location thermal segregation was detected If density profile fails – contractor waives QCQA production and placement bonus If density profile passes – QCQA bonus if applicable will be paid provided contractor provides all documentation of thermal and density profiles When Severe Thermal Segregation (> 50°F) is Detected If Contractor uses hand held thermometer or thermal camera for specification compliance Suspend operation & take immediate corrective action No applicable QCQA bonus will be paid for production or placement if severe thermal segregation is identified If density profile fails – Contractor must remove and replace the sublot Report test results Subject to: No production & placement bonuses Remove & replace with surface irregularities Corrective action Suspension of paving operations Pass Immediate Corrective action Subject to: No production & placement bonuses Suspension of paving operations Immediate corrective Action Perform density profile Remove & replace with failing density profile Report test results Perform density profile

Previous Slide Use of Pave-IR YES Provide Engineer electronic (or when Pave-IR is used for informational only) NOT required to measure & document HMA temp and station # on each Haul ticket Allowed to pave when roadway is dry & surface temperature is at least 32°F Thermal profile Density profiles NOT required Specify use for spec compliance Review output daily Provide Engineer output files daily Modify paving process Moderate thermal segregation thermal differential 25 - 50°F Pass Severe thermal segregation > 50°F Subject to: Suspension of paving operations Provide Engineer electronic copies of all daily data files Temperature differential < 25ºF NO When Moderate Thermal Segregation (25°F – 50°F) is Detected If Contractor uses Pave-IR for specification compliance Modify the paving process as necessary to eliminate any (moderate or severe) thermal segregation identified by the Pave-IR system. No further action (density profile) required QCQA bonus if applicable will be paid provided contractor provides automated documentation of Pave-IR output When Severe Thermal Segregation (> 50°F) is Detected Engineer may suspend operations if recurring severe thermal segregation is identified.

When Moderate Thermal Segregation (25°F – 50°F) is Detected If Contractor uses hand held thermometer or thermal camera for specification compliance: Take corrective action and: Perform a density profile at the location thermal segregation was detected If density profile fails – contractor waives QC/QA production and placement bonus If density profile passes – QC/QA bonus if applicable will be paid provided contractor provides all documentation of thermal and density profiles If Contractor uses Pave-IR for specification compliance Modify the paving process as necessary to eliminate any (moderate or severe) thermal segregation identified by the Pave-IR system. No further action (density profile) required QCQA bonus if applicable will be paid provided contractor provides automated documentation of Pave-IR output

When Severe Thermal Segregation (> 50°F) is Detected If Contractor uses hand held thermometer or thermal camera for specification compliance Suspend operation & take immediate corrective action No applicable QC/QA bonus will be paid for production or placement if severe thermal segregation is identified Perform a density profile at the location thermal segregation was detected If density profile fails – Contractor must remove and replace the sublot If Contractor uses Pave-IR for specification compliance Engineer may suspend operations if recurring severe thermal segregation is identified. No further action (density profile) required QC/QA bonus if applicable will be paid provided contractor provides automated documentation of Pave-IR output.

Conclusions “What Gets Measured Gets Done” TxDOT, along with Industry, is implementing better specifications and better techniques to address the problem of thermal segregation 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 and cures Every contractor that has used the Pave-IR system states that they have improved their paving process from the feedback they get from the system. “What Gets Measured Gets Done”

Questions? Russel W. Lenz, P.E. Director, Construction Division Russel.Lenz@txdot.gov (512) 416-2559 Dale A. Rand, P.E. Construction Division, Flexible Pavements Branch Dale.Rand@txdot.gov (512) 506-5836