Evaluation of NDTE Technologies for Airport Pavement Maintenance

Evaluation of NDTE Technologies for Airport Pavement Maintenance and Acceptance Activities Imad L. Al-Qadi John S. Popovics Wei Xie Sara Alzate University of Illinois at Urbana-Champaign

Outline • Project Scope and Objectives • NDTE State-of-art report: Promising NDTE technologies to assess existing and new airport pavements • Future Work

Objectives • To determine the effectiveness and practicality of new and existing NDTE technologies for maintenance, evaluation, quality control and acceptance of flexible airport pavements • To evaluate and recommend appropriate NDTE technologies to the FAA based on field evaluation results

Scope of work Review and summarize existing and new NDTE technologies State-of-the-art report New research Identify current NDTE needs for airport pavements and facilities Identify promising NDTE technology (technical and practical suitability) Field testing and analysis of promising NDTE technology Final report

NDTE State-of-the-art Report • Existing NDTE methods are summarized in a draft report, for FAA review and comment • Each method is presented in a chapter: – – – – 1) Impact-echo 2) Surface waves 3) Sonic/ultrasonic 4) Nuclear radiometry 5) Infrared thermography 6) GPR 7) Laser profiling 8) Digital imaging

NDTE State-of-the-art Report • Each chapter discusses the following: – – – Theory Equipment Benefits and applications Limitations Recent developments

Nuclear Density Gauge • • The radiation intensity of gamma rays that passes through a medium, or is scattered back from a medium, is used to measure density. Nuclear density gauges are compact and provide direct and rapid measurements

Application of Nuclear Density Gauge • Measuring in-situ HMA, concrete and solid densities • Suitable for both thin and thick layers; better for thick layers.

Limitations of Nuclear Density Gauge • Need for calibration • Affected by lift thickness and variability of supporting layer • Difficulties in identifying levels of segregation • High initial cost, certification requirement, periodic inspection, and difficulties in shipping and transport and disposal.

Impact Echo Resonant frequency interpreted for thickness information

Application of Impact-echo • Measuring concrete slab thickness • Identifying location and depth of delamination defects in concrete

Limitations of Impact-echo • Local, point contact measurement • Not effective for HMA pavements • Only effective for top layer in pavement system • Difficulties in locating small defects

Surface Waves (Spectral/Multiple Analysis of Surface Waves (SASW/ MASW) Measure dispersion of surface waves in layered media

Application of surface waves • Estimate pavement layer properties (thickness and modulus) Estimated stiffness profile Portable Seismic Pavement Analyzer (PSPA) for SASW

Interpretation of MASW Lamb wave curve best fit to data to give layered structure Stacked multiple signal data MASW mapping of signal data

Limitations of surface wave • Local, point contact measurement • Data inversion is complicated (MASW approach has sounder technical basis than SASW) • Not reliable for accurate thickness measurements of a specific layer

Sonic/ Ultrasonic http: //www. cflhd. gov/agm/eng. Applications/Pavements/413 Spec. Analy. Surf. Waveand. Ultr. Sonic. Surf. Wave. Methods. htm Δt Δt Measure velocity of various wave modes propagating in pavement and relate to mechanical properties

Application of sonic/ ultrasonic • Estimate mechanical properties of pavement (Modulus, strength, damage level, etc. ) • Locate voids/ interfaces

Limitations of sonic/ ultrasonic • Local, point contact measurement • Estimation of absolute values of modulus and strength of concrete is not accurate

Digital Imaging Technology • Automated digital imaging system consists of image acquisition and distress image processing After Huang et al. 2006

Equipment and Data Collection • DMI is used to control the acquisition of digital image • Distress detection, isolation, classification, segmentation, and compress • Fast wavelet transform for the wavelet-based distress detection, isolation, and evaluation

Application of Video Imaging • Segregation measurement: – Identify texture variation related to HMA segregation – Use GLCM technique to identify segregation • Crack Detection/ Surface Distress – Individual crack information can be vectorizing – Wise. Crax is used to automatically detect cracks, classify and generate crack map – Recent development uses processing algorithm for high-speed, real-time inspection of pavement cracking

Limitations of Imaging Technique • Video image can only detect surface distress • There is environmental requirement during data collection • The system is vulnerable to vehicle vibration • Video image can measure gradation segregation level; but not temperature segregation

Laser Technique • • Pavement surface information can be determined by the movement of reflected beam spot on the detector It can supply rapid, continuous, and high accurate measurement

Equipment and Data Collection Two types of laser camera are available to digitally image pavement surface: area scan and line scan Line scan and area scan laser systems (Xu et al. 2006)

Friction and Roughness Measurements • For friction use high-pass filter with 50 mm wavelength cutoff • For roughness use low-pass filter with 0. 5 m wavelength cutoff Texture Classification Microtexture Macrotexture Megatexture Relative Wavelength λ<0. 5 mm 0. 5 mm < λ < 50 mm < λ < 500 mm Roughness 0. 5 m < λ < 50 m

Applications • Detect segregation: – texture ratio of segregated to non-segregated area to measure segregation level • Rutting measurements: – Automatic, rapid and continuous • Crack measurements: – – Valley detection of candidate cracks Validation algorithm Characterize crack types and pattern 3 D laser imaging has been introduced

Limitations • It provides pavement surface condition only • Difficult to distinguish between texture and crack • Transversal cracks are likely to be detected, while longitudinal cracks are easily missed • Narrow and shallow cracks may be filtered out during data processing

Infrared Thermography • Infrared thermography is standardized by ASTM D 4788. It includes passive and active methods • Subsurface changes in pavements generate surface temperature variations

Equipment and Data Collection Infrared sensors bar

Applications • QC/QA • Segregation measurement • Crack and defect measurement detection Defect

Limitations • It is applied for near-surface surveys • It cannot distinguish between gradation and temperature segregation • For existing pavements, it depends on solar energy

Ground Penetrating Radar • Ground Penetrating Radar (GPR) is a special kind of RADAR • Purpose of using GPR: – Detect targets buried in a dielectric medium – Estimate their depths • GPR applications: geophysics, archeology, law enforcement, evaluation of civil structures (buildings, bridges, pavements)

Principle of GPR Transceiver Control Unit Antenna Layer 1 Layer 2 DMI

GPR Antennae • Ground-coupled antenna: in contact with ground surface • Air-coupled antenna: 1 to 2 ft above surface Ground Coupled Antenna Horn Antennae

Typical GPR Response (scan) A 0 HMA t 1 HMA t 2 Base A 1 Base Subgrade A 2 Subgrade

GPR Data Collection HMA Base Subgrade

Layer Thickness Estimation Thickness of i th A 0 layer: t 1 , d 1 HMA r, 1 A 1 Base t 2 , d 2 r, 2 Subgrade r, 3 A 2

New Pavements (QC/QA ) Classic GPR thickness estimation gives accurate results:

GPR Accuracy: New Pavements

Dielectric Constant Using CMP Common midpoint (CMP) technique (or commondepth point, CDP) is used as follows: x T HMA er 1 T/R R t 1 h t 2 P : EM velocity in the layer

Modified CMP Technique Modified common midpoint technique: Snell’s law of refraction: x 0 T air er 0=1 PCC er 1 (1) R x 1 i h 0 T/R t 1 t (2) t 2 P Using the figure: h 1 (3) (4)

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Depth Resolution Enhancement Surface Reflection WS BM-25. 0 HMA/Base Reflection OGDL Base Reflection Overlap Base/Subgrade Reflection Surface Reflection WS/BM-25. 0 Reflection BM-25. 0/OGDL Reflection OGDL/Base Reflection Base/Subgrade Reflection Measured Signal from: Thin layer interfaces not visible because of reflection overlap Synthesized Signal

Measured vs. Simulated Signal

Layer Thickness Estimation by Iteration Raw GPR Data Preprocessing Layer Interface Detection Dielectric Properties Estimation Layer Thicknesses

Detection Results WS BM-25. 0 OGDL Base Copper plates Detected Layer Interfaces

GPR Data Analysis Software Channel 1 Channel 2

Density Measurement with GPR • According to volumetric mixture theory, HMA dielectric constant depends on aggregate, binder and air volumes Note: calibration coefficients (a and b) are determined from field cores. • • • A drop in dielectric value may indicate a density change 2 GHz antenna is preferred It has potential…. it requires more investigation

Defects Detection with GPR • Segregation: locations of course-graded and dense-graded mixes has been reported • Stripping: additional reflections appear between surface and layer interface • Moisture content: relationship between dielectric constant and moisture content

Locating Reinforcement (CRCP) Transversal Reinforcement Concrete Asphalt OGDL Longitudinal Reinforcement Copper Plate under Slab Ground-Coupled Data, CRCP, VA. Smart Road

GPR Application on Composite Pavement Measure overlay thickness and detect overlaid joints: Surface 8 in Overlay 3 ft Rebar 100 ft Joint Spacing Interface of HMA and PCC ISAC

Limitations of GPR Technique • Air-coupled antenna has limited penetration depth • GPR survey requires dry pavement condition • Errors may result from dielectric constant estimates from surface reflection • Cores may be needed to determine calibration coefficients • Strong reflection may mask weak signals • Accuracy of GPR results depends on adopted data analysis technique

Future Work • During this project year, we aim to – Identify current NDTE needs for airport flexible pavements – Identify promising NDTE technology, and carry out new research efforts to meet those needs