UNDERSTANDING PAVE-IR
Background, Use, and Advanced Techniques
Dale Rand (TxDOT)Richard Izzo (TxDOT)Stephen Sebesta (TTI)
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
MODULE 1Introduction to Thermal Profiling
and Pave-IR
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)
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
y = 0.2415xR2 = 0.9027
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0
5
10
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Change in Temp (F)
Cha
nge
in D
ensi
ty (p
cf)
Spec max density differential = 6 pcf
6 pcf density differential at ~ 25 F
temp differential
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
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.
Common Performance Problems
Early observations:
coarser texture and holding
water
Raveling and Cracking Follow
Fatigue Life Substantially Reduced
Source: NCAT (2000)
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
Contrast of Overlays
Thermally Segregated Not Thermally Segregated
Sampling Distributions of Segregated and Non-Segregated HMA
Common Patterns of Thermal Segregation
Truck-end Streaks Random Production
temperature changes
Paver stops
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
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316 314
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320 314 310
Example Truck-End
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
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
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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
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
Measuring Thermal Segregation Test Method Tex-244-F
Handheld IR thermometer
Thermal camera Pave-IR
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
Thermal profiling with handheld IR thermometer or thermal camera according to Test Method Tex-
244-F
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
Comparison of Thermal Profiling Techniques
Test Device Strengths Weaknesses
Handheld IR Thermometer
Inexpensive.Simple to use.
Tests independent of paving train.
Requires constant operator attendance.May miss localized
defects.
IR Camera
Inexpensive.Simple to use.
Tests independent of paving train.
More coverage than thermometer.
Requires constant operator attendance.May miss localized
defects.
Pave-IR
Does not require constant operator attendance.
Provides real-time feedback.Tests virtually full-coverage.Automated data reduction.
Most costly device.Testing coverage
could impact risk of finding defects.
May include artificial cold spots in data set.
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
QUESTIONS….