Understanding Pave- ir

1. Understanding Pave-ir Background, Use, and Advanced Techniques Dale Rand (TxDOT) Richard Izzo (TxDOT) Stephen Sebesta (TTI)

2. Introduction by TxDOT • Why Has TxDOT Implemented Pave-IR? • Promote more uniform, higher quality pavements • Minimize/eliminate thermal segregation • Expand range of weather conditions for paving • Special Provision 341-024 • Contains option for contractor to use Pave-IR • If using Pave-IR, density profiles are not required and are not applicable • Tex-244-F • Modified to include thermal profiling with handheld infrared thermometer, thermal camera, or Pave-IR

3. Module 1 Introduction to Thermal Profiling and Pave-IR

4. . Background to Thermal Segregation • 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)

5. 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

6. Why Is Thermal Segregation Important? • Recall cold spots typically become low density • Density is the primary contributor to performance • Contractor and agency risk are impacted • Acceptance and pay schedules are based on density • Segregated locations distress prematurely

7. 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.

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

9. Raveling and Cracking Follow

10. Fatigue Life Substantially Reduced Source: NCAT (2000)

11. Thermal Segregation Impacts Risk • 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

12. Contrast of Overlays Thermally Segregated Not Thermally Segregated

13. Sampling Distributions of Segregated and Non-Segregated HMA

14. Common Patterns of Thermal Segregation • Truck-end • Streaks • Random • Production temperature changes • Paver stops

15. Truck-End Thermal Segregation • 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

16. Example Truck-End 314 316 220 220 240 215 320 314 310

17. Thermal Streaks • 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

18. Random Thermal Segregation • Localized cold spots with no apparent pattern • May be small clumps of mix; in some cases these are removed by paving crew 249 309 306 270 255

19. Changes in Production Temperature • 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

20. Paver Stops • Cold spot, often followed by localized hot spot from paver burners • Per Tex-244-F these sections are excluded from thermal profile analysis

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

22. Using the Handheld IR Thermometer and Camera • 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

23. Thermal profiling with handheld IR thermometer or thermal camera according to Test Method Tex-244-F

24. Using Pave-IR • 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-ft

25. Comparison of Thermal Profiling Techniques

26. IR Thermometer Method Can Miss Localized Spots • 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

27. Questions….