Presentation on theme: "Implementation of the Pave-IR System in Texas"— Presentation transcript:
1 Implementation of the Pave-IR System in Texas Russel Lenz, P.E.TxDOT Construction DivisionDivision DirectorVirginia BeachAugust 3, 2011
2 BackgroundHistorically, 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.
5 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 stopsAnd at locations where thermal segregation is identifiedAnd where visible segregation is identifiedContractor waives QC/QA bonus if profile failsRemove 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.
6 Implementation of the Pave-IR System Goal: Improved pavement performance by encouraging Contractors to improve paving operationsOptional for use on TxDOT HMA paving projectsTxDOT specifications incentivesNo density or thermal profilesOpportunity 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
7 Implementation of the Pave-IR System TxDOT specifications incentives (cont’d)Used in lieu of an MTD – End dumps not allowed w/o MTDAutomated documentationContractor’s ticket taker not required to measure mix temperature and record station # on haul ticketsOther minor incentives included in specification
8 Thermally segregated locations holding water .Thermal Segregation - BackgroundHistorically segregation thought of as mechanical (gradation) phenomenon1996 – WSDOT discovered thermal imaging could detect segregationCold spots became low density areas89 percent of locations with ∆t > 25°F failed density uniformity criteriaThermal 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
9 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
10 NCAT (2000) and TTI (2002) similarly found thermal uniformity suitable for detecting segregation NCAT – low severity segregation when ∆t > 18°FTTI – when ∆t > 25°F, TxDOT density uniformity requirements not met10
11 Why is Thermal Segregation Important? Cold spots typically indicate low density areasDensity is “a” or “the” primary contributor to pavement performanceContractor and agency risk are impactedAcceptance and pay schedules are based on densitySegregated locations distress prematurelyRide quality ultimately impacted by thermal segregation
12 Early observations: coarser texture and holding water Common Performance ProblemsEarly observations: coarser texture and holding water
14 Fatigue Life Substantially Reduced Even moderate (>25 but < 50 F) thermal segregation can result in substantially reduced pavement life.Source: NCAT (2000)14
15 Common Methods of Measuring Thermal Segregation Infrared Thermometers – less than $200Infrared Cameras – less than $5KPave-IR System – less than $30K
16 Measuring Thermal Segregation Test Method Tex-244-FHandheld IR thermometerThermal cameraPave-IR
17 Current Usage of Pave-IR Texas – 25+ UnitsOther users:MinnesotaWisconsinNCATOther interested regions:WashingtonAlaskaQuebecOhioMichiganGermanyChinaAs of September 2010 these are the current users, and agencies/regions that have expressed interest in demonstrations17
18 Test Device Strengths Weaknesses Handheld IR ThermometerInexpensive.Simple to use.Tests independent of paving train.Requires constant operator attendance.May miss localized defects. No permanent record.IR CameraMore coverage than thermometer.May miss localized defects. No permanent record (usually).Pave-IRDoes 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.
19 Pave-IR Summary Results Screen Summary Results during Data CollectionPress 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 Screen19
20 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 good20
21 Note report pages 3 & 4 are just continuations of profiles without thermal segregation 21
25 Next Slide All circumstances require NO reporting of test results (or when Pave-IR is usedfor informational only)Use ofPave-IRYESMeasure temperature of HMA &document with Station #on each haul ticketNext SlideComply withpavement surfacetemperature requirementsPerform density profilesPaver stopsThermal segregationVisibly segregated areas1 per sublotPerform Thermal profiles1 per sublotHandheld thermometerThermal cameraPassFailTemperaturedifferential< 25ºFModeratethermal segregationThermal differential°FSevere thermalsegregationThermal differential> 50°FWhen Moderate Thermal Segregation (25°F – 50°F) is DetectedIf 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 detectedIf density profile fails – contractor waives QCQA production and placement bonusIf density profile passes – QCQA bonus if applicable will be paid provided contractor provides all documentation of thermal and density profilesWhen Severe Thermal Segregation (> 50°F) is DetectedIf Contractor uses hand held thermometer or thermal camera for specification complianceSuspend operation & take immediate corrective actionNo applicable QCQA bonus will be paid for production or placement if severe thermal segregation is identifiedIf density profile fails – Contractor must remove and replace the sublotReporttestresultsSubject to:No production &placement bonusesRemove & replace withsurface irregularitiesCorrective actionSuspension ofpaving operationsPassImmediateCorrectiveactionSubject to:No production &placement bonusesSuspension ofpaving operationsImmediate correctiveActionPerform density profileRemove & replace withfailing density profileReporttestresultsPerformdensity profile
26 Previous Slide Use of Pave-IR YES Provide Engineer electronic (or when Pave-IR is usedfor informational only)NOT required to measure &document HMA tempand station # on eachHaul ticketAllowed to pavewhen roadway is dry &surface temperatureis at least 32°FThermalprofileDensity profilesNOTrequiredSpecify use for speccomplianceReview output dailyProvide Engineer output files dailyModifypaving processModeratethermal segregationthermal differential°FPassSevere thermalsegregation> 50°FSubject to:Suspension ofpaving operationsProvide Engineer electroniccopies of all daily data filesTemperaturedifferential< 25ºFNOWhen Moderate Thermal Segregation (25°F – 50°F) is DetectedIf Contractor uses Pave-IR for specification complianceModify the paving process as necessary to eliminate any (moderate or severe) thermal segregation identified by the Pave-IR system.No further action (density profile) requiredQCQA bonus if applicable will be paid provided contractor provides automated documentation of Pave-IR outputWhen Severe Thermal Segregation (> 50°F) is DetectedEngineer may suspend operations if recurring severe thermal segregation is identified.
27 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 detectedIf density profile fails – contractor waives QC/QA production and placement bonusIf density profile passes – QC/QA bonus if applicable will be paid provided contractor provides all documentation of thermal and density profilesIf Contractor uses Pave-IR for specification complianceModify the paving process as necessary to eliminate any (moderate or severe) thermal segregation identified by the Pave-IR system.No further action (density profile) requiredQCQA bonus if applicable will be paid provided contractor provides automated documentation of Pave-IR output
28 When Severe Thermal Segregation (> 50°F) is Detected If Contractor uses hand held thermometer or thermal camera for specification complianceSuspend operation & take immediate corrective actionNo applicable QC/QA bonus will be paid for production or placement if severe thermal segregation is identifiedPerform a density profile at the location thermal segregation was detectedIf density profile fails – Contractor must remove and replace the sublotIf Contractor uses Pave-IR for specification complianceEngineer may suspend operations if recurring severe thermal segregation is identified.No further action (density profile) requiredQC/QA bonus if applicable will be paid provided contractor provides automated documentation of Pave-IR output.
29 Conclusions “What Gets Measured Gets Done” TxDOT, along with Industry, is implementing better specifications and better techniques to address the problem of thermal segregationThe Pave-IR System is an excellent “Passive Inspection” device that allows end result versus method specificationsIt allows contractors to see what they are doing and improve their operationsContractors can focus on causes and curesEvery 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”
30 Questions? Russel W. Lenz, P.E. Director, Construction Division (512)Dale A. Rand, P.E.Construction Division, Flexible Pavements Branch(512)