National Academies Press: OpenBook

Nondestructive Testing to Identify Delaminations Between HMA Layers, Volume 2 - Theoretical Models (2013)

Chapter: Chapter 2 - Theoretical Models for Infrared Thermography Technology

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Suggested Citation:"Chapter 2 - Theoretical Models for Infrared Thermography Technology." National Academies of Sciences, Engineering, and Medicine. 2013. Nondestructive Testing to Identify Delaminations Between HMA Layers, Volume 2 - Theoretical Models. Washington, DC: The National Academies Press. doi: 10.17226/22603.
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Suggested Citation:"Chapter 2 - Theoretical Models for Infrared Thermography Technology." National Academies of Sciences, Engineering, and Medicine. 2013. Nondestructive Testing to Identify Delaminations Between HMA Layers, Volume 2 - Theoretical Models. Washington, DC: The National Academies Press. doi: 10.17226/22603.
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Suggested Citation:"Chapter 2 - Theoretical Models for Infrared Thermography Technology." National Academies of Sciences, Engineering, and Medicine. 2013. Nondestructive Testing to Identify Delaminations Between HMA Layers, Volume 2 - Theoretical Models. Washington, DC: The National Academies Press. doi: 10.17226/22603.
×
Page 10
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Suggested Citation:"Chapter 2 - Theoretical Models for Infrared Thermography Technology." National Academies of Sciences, Engineering, and Medicine. 2013. Nondestructive Testing to Identify Delaminations Between HMA Layers, Volume 2 - Theoretical Models. Washington, DC: The National Academies Press. doi: 10.17226/22603.
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Page 11

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8Theoretical Models for Infrared Thermography Technology The numerical simulations presented in this chapter were carried out by Infrasense with support from Dr. Kim Belli of Northeastern University in Boston, Professor Dennis Hiltunen of the University of Florida, and Professor Rajib Mallick of Worcester Polytechnic Institute. Numerical simulations of nondestructive testing (NDT) techniques were carried out to assess the NDT ability to detect delaminations and to evaluate the most promising configu- rations for implementing each NDT method. An NDT tech- nique and/or configuration that does not show promise in the numerical simulations would not likely succeed in the field evaluations. Therefore, results obtained from the simulations would help the project team focus on the most promising methods or configurations, or both, in the laboratory and field evaluations. The numerical simulations were conducted by using exist- ing numerical models to simulate and compare simulation results of delaminated and intact pavements. The simula- tion information was used to define detectability and served to support recommendations of specific methods or con- figurations, or both, for the laboratory and field evalua- tions. Modeling provided insight into results that could be expected from laboratory and field experiments, and also offered guidance into the effective configurations of the transmitter and receiver for each NDT technique. Mod- eling results were considerably cleaner than were results obtained in the laboratory and field evaluations, and mod- eling results were based on certain idealizations of mate- rial characteristics and input signals. Simulation results showed (a) whether, under ideal conditions, the pavement defect could be detected; and (b) under what conditions detectability could be enhanced. For electromagnetic and mechanical wave methods, the simulation results could show how the relative placement of the source and receiver could affect the NDT detectability. Model Description The use of infrared (IR) thermography is based on the detec- tion of surface thermal anomalies associated with subsur- face defects. Those anomalies develop under the influence of solar heating and cooling. To evaluate the potential effective- ness of this method, thermal models were used to calculate the magnitude of surface thermal anomalies associated with delamination. The modeling was carried out by using the heat transfer module from COMSOL Multiphysics software. The basic model setup is shown in Figure 2.1. Solar radiation is typically modeled as a parabolic input radiation pattern from sunrise to sunset, with radiational cool- ing and convection to ambient temperature taking place when there is no sunshine. For simplicity, the COMSOL model was used as a triangular input, as shown in Figure 2.2. Two types of solar inputs were considered. The first type was a continu- ous solar input assuming that the pavement was continuously exposed to the sun. The second type assumed that the solar input was blocked for a period of time after time tb. The other parameters used for the modeling effort were • h = AC thickness = 200 mm; • d = delamination depth = 50 mm; • ds = thickness of stripped layer = 15 mm; • dd = thickness of delamination = 1 mm; • Qmax = 800, w/m2; • tb = 11 a.m., 1 p.m., and 3 p.m.; and • w = width of partial delamination = 60 mm. The ambient temperature profile was 40°F (5°C used) from midnight to 6 a.m., increased linearly to 65°F (20°C used) from 6 a.m. to noon, decreased linearly to 40°F (5°C used) from noon to 6 p.m., and constant as 40°F (5°C used) from 6 p.m. to mid- night. The thermal properties of the components in each model are shown in Table 2.1. C h a p t e r 2

9 R(t) h h h h w d d air gap air gap σd σd d σd T(t) R(t) = input solar radiation T(t) = measured surface temp. (a) Model A – Intact Asphalt Layers. (b) Model B – Debonded Asphalt Layers. (c) Model B – Partially Debonded Asphalt Layers. (d) Model C – Stripped Asphalt. stripped material. Figure 2.1. Structure of asphalt thermal models. R(t) time 12AM 6AM 12noon 6PM 12 Qmax R(t) time 12AM 6AM 12noon 6PM 12 tb (a) (b) Figure 2.2. Solar radiation patterns: (a) solar input blocked after time tb and (b) normal solar radiation. Table 2.1. Thermal Properties of Components in Each Model Component Thermal Conductivity (W/m?K) Heat Capacity (J/kg?K) Density (kg/m3) Intact asphalt 1 1,100 2,300 Stripped asphalt (1) 1 1,100 1,800 Stripped asphalt (2) 0.75 1,100 1,800 Stripped asphalt with 10% water 0.95 1,408 2,170 Air at 25°C 0.026 1,006.25 1.1843 Water at 25°C 0.6 4,186 1,000

10 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 Te m pe ra tu re D iff er en tia l, °C Time (hour) Model C-A (k=1.0) Model C-A (k=0.75) Figure 2.3. Results for dry stripped layer. -3 -2 -1 0 1 2 3 4 5 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 Te m pe ra tu re D iff er en tia l, °C Time (hour) air-filled delamination Water-filled delamination Figure 2.4. Results for air- and water-filled delamination. The simulations carried out with the models were as follows: • Model A, normal solar input; • Model A, blocked solar input; • Model B, wet and dry delamination; • Model B, partial delamination; • Model C, stripped asphalt, k = 1.0; and • Model C, same as Model C above, with k of stripped material = 0.75. Discussion of results Sample results of these simulations are shown in Figures 2.3 through 2.5. The results in each figure show the tempera- ture differential, which is the temperature response for each condition minus the temperature response for the intact con- dition (Model A). A typical commercial IR camera used for capturing images of asphalt pavements can distinguish temperature differ- entials on the order of 1°C. On the basis of results shown in Figure 2.3, it appeared that the temperature differentials produced by a dry stripped pavement layer were below the threshold of detectability. On the other hand, the results in Figure 2.4 for the air-filled delamination showed temperature differentials of up to 3°C, which were within the detectable range. In Figure 2.5, the model represented a delaminated layer interface with partial contact and smaller air gaps. Using this representation, the maximum temperature differential decreased by half, and the likelihood of detection was reduced. Unlike with GPR, introducing moisture into the delamination or stripped area reduced the likelihood of detection.

11 -1.5 -1 -0.5 0 0.5 1 1.5 2 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 Te m pe ra tu re D iff er en tia l, °C Time (sec) wet stripping partial delamination Figure 2.5. Results for partial delamination and wet stripped layer.

Next: Chapter 3 - Theoretical Models for Mechanical Wave Technology: Impact Echo, Impulse Response, and Ultrasonic Surface Waves »
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 Nondestructive Testing to Identify Delaminations Between HMA Layers, Volume 2 - Theoretical Models
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TRB’s second Strategic Highway Research Program (SHRP 2) Report S2-R06D-RW-2: Nondestructive Testing to Identify Delaminations Between HMA Layers, Volume 2 describes the theoretical models used in the development of nondestructive testing (NDT) techniques capable of detecting and quantifying delaminations in HMA pavements.

SHRP 2 Report S2-R06D-RW-2 was developed as part of SHRP 2 Renewal Project R06D, which generated a sizable amount of documentation regarding the findings of evaluations and equipment development. The report for SHRP 2 Renewal Project R06D is therefore divided into five volumes. Volume 1 is a comprehensive summary of the study. Volumes 2 through 5 provide more detailed technical information and are web-only. The topics covered in other volumes are listed below.

Volume 3: Controlled Evaluation Reports

Volume 4: Uncontrolled Evaluation Reports

Volume 5: Field Core Verification

Renewal Project R06D also produced a Phase 3 Report to document guidelines for use of ground penetrating radar and mechanical wave nondestructive technologies to detect delamination between asphalt pavement layers.

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