Understanding Pave- ir

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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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….