Parisa Shokouhi

Nondestructive Testing to Identify Concrete Bridge Deck Deterioration

This work was sponsored by the Federal Highway Administration in cooperation with the American Association of State Highway and Transportation Officials. It was conducted in the second Strategic Highway Research Program (SHRP 2), which is administered by the Transportation Research Board of the National Academies. The project was managed by Monica Starnes, Senior Program Officer for SHRP 2 Renewal. The research reported herein was performed by the Center for Advanced Infrastructure and Transportation (CAIT) at Rutgers University (RU); the Center for Transportation Infrastructure Systems (CTIS) at The University of Texas at El Paso (UTEP); the Federal Institute for Materials Research and Testing (BAM), Germany; and Radar Systems International, Inc. (RSI). Rutgers University was the coordinator and contractor for this project. Dr. Nenad Gucunski, professor and chair of Civil and Environmental Engineering and director of CAIT’s Infrastructure Condition Monitoring Program at RU, was the principal investigator. The other authors of this report are Dr. Soheil Nazarian, professor of Civil Engineering and director of CTIS at UTEP; Dr. Deren Yuan, research associate at CTIS at UTEP; Dr. Herbert Wiggenhauser, head of Non-Destructive Testing (NDT) in Civil Engineering at BAM; Dr. Alexander Taffe, leader of Combination and Automation of NDT of Buildings at BAM; Dr. Parisa Shokouhi, Alexander von Humboldt Research Fellow, hosted by BAM; and Doria Kutrubes, president of RSI. Arezoo Imani and Touraj Tayebi, graduate research assistants at RU, helped conduct the validation testing, data analysis, and web manual content preparation. Hoda Azari, a graduate research assistant, and Dr. Manuel Celaya, a research engineer at UTEP, assisted in the validation study as well. Hooman Parvardeh, research assistant at RU, helped build the reference database and develop the framework for the web manual, while Erica Erlanger, a research staff member at RU, edited the manuscript. Their contributions are gratefully acknowledged. The research team also gratefully acknowledges contributions of the participants from industry and academia in the validation testing. The participants include NDT Corporation; Germann Instruments; Olson Engineering; Dr. Ralf Arndt, National Research Council associate at FHWA Turner–Fairbank Highway Research Center; Ingegneria Dei Sistemi S.p.A. (IDS), Italy; 3D-RADAR, Norway; Dr. John Popovics, University of Illinois at Urbana-Champaign; Dr. Jinying Zhu, The University of Texas at Austin; Rutgers University—Center for Advanced Infrastructure and Transportation; and The University of Texas at El Paso—Center for Transportation Infrastructure Systems. The contributions of these participants were critical for the evaluation and grading of the performance of NDT technologies.

A set of measures for the systematic classification of the nonlinear elastic behavior of disparate rocks

Dynamic acoustoelastic testing is performed on a set of six rock samples (four sandstones, one soapstone, and one granite). From these studies at 20 strain levels 10 −7 <�� < 10 −5 , four measures characterizing the nonlinear elastic response of each sample are found. Additionally, each sample is tested with nonlinear resonant ultrasonic spectroscopy and a fifth measure of nonlinear elastic response is found. These five measures of the nonlinear elastic response of the samples (approximately 3 × 6 × 20 × 5 numbers as each measurement is repeated 3 times) are subjected to careful analysis using model-independent statistical methods, principal component analysis, and fuzzy clustering. This analysis reveals differences among the samples and differences among the nonlinear measures. Four of the nonlinear measures are sensing much the same physical mechanism in the samples. The fifth is seeing something different. This is the case for all samples. Although the same physical mechanisms (two) are operating in all samples, there are distinctive features in the way the physical mechanisms present themselves from sample to sample. This suggests classification of the samples into two groups. The numbers in this study and the classification of the measures/samples constitute an empirical characterization of rock nonlinear elastic properties that can serve as a valuable testing ground for physically based theories that relate rock nonlinear elastic properties to microscopic elastic features.

Surface Wave Velocity-Stress Relationship in Uniaxially Loaded Concrete

The deterioration of concrete due to excessive loading, freezing and thawing, corrosion of reinforcement, or alkali-silica reaction (ASR) begins with subtle changes in its microstructure and microcracking. The sonic surface wave velocity measured on prismatic concrete specimens under uniaxial compression was found to be highly stress-dependent. At low stress levels, the acoustoelastic effect and the closure of existing microcracks results in a gradual increase in surface wave velocities. At higher stress levels, concrete suffers irrecoverable damage: the existing microcracks widen and grow together and new microcracks form. This progressive damage process leads first to the flattening and eventually the drop in the velocity-stress curves. Measurements on specimens undergoing several loading cycles revealed that the velocities show a stress-memory effect. Comparing the velocities measured during loading and unloading, the effects of stress and damage on the measured velocities could be differentiated. The stress dependency of surface wave velocity proved to be direction-dependent. The velocity increases and decreases the most when measured parallel and perpendicular to the loading axis, respectively.

Frequency, pressure, and strain dependence of nonlinear elasticity in Berea Sandstone

Acoustoelasticity measurements in a sample of room dry Berea sandstone are conducted at various loading frequencies to explore the transition between the quasi‐static ( ) and dynamic (few kilohertz) nonlinear elastic response. We carry out these measurements at multiple confining pressures and perform a multivariate regression analysis to quantify the dependence of the harmonic content on strain amplitude, frequency, and pressure. The modulus softening (equivalent to the harmonic at 0f) increases by a factor 2–3 over 3 orders of magnitude increase in frequency. Harmonics at 2f, 4f, and 6f exhibit similar behaviors. In contrast, the harmonic at 1f appears frequency independent. This result corroborates previous studies showing that the nonlinear elasticity of rocks can be described with a minimum of two physical mechanisms. This study provides quantitative data that describes the rate dependency of nonlinear elasticity. These findings can be used to improve theories relating the macroscopic elastic response to microstructural features.

Nondestructive Investigation of Stress-Induced Damage in Concrete

The changes in the sonic surface wave velocity of concrete under stress were investigated in this paper. Surface wave velocities at sonic frequency range were measured on a prismatic concrete specimen undergoing several cycles of uniaxial compression. The loading was applied (or removed) gradually in predefined small steps (stress-controlled). The surface wave velocity was measured at every load step during both loading and unloading phases. Acoustic Emission (AE) test was conducted simultaneously to monitor the microcracking activities at different levels of loading. It was found that the sonic surface wave velocity is highly stress dependent and the velocity-stress relationship follows a particular trend. The observed trend could be explained by a combination of acoustoelasticity and microcracking theories, each valid over a certain range of applied stresses. Having measured the velocities while unloading, when the material suffers no further damage, the effect of stress and damage could be differentiated. The slope of the velocity-stress curves over the elastic region was calculated for different load cycles. This quantity was normalized to yield a dimensionless nonlinear parameter. This parameter generally increases with the level of induced damage in concrete.

Assessment of Debonding in Concrete Slabs Using Seismic Methods

A combination of impact echo (IE) and ultrasonic surface waves techniques was used to locate the debonding in concrete slabs at several locations on TX-225 near Houston, Texas. A portable seismic pavement analyzer (PSPA), a hand-held automated system, was used for seismic data collection in the field. Field measurements are presented in the time and frequency domains in the form of time records and amplitude spectra. The characteristics differentiating the response (time records) of fully bonded and debonded slabs are discussed. The frequency domain (spectral) analysis was shown to be superior to time domain analysis in describing the response of slabs in marginal condition (i.e., slabs showing partial debonding or horizontal cracks). On the basis of the spectral characteristics of their surface response, the slabs were categorized into four different categories: good, fair, poor, and bad conditions (in terms of debonding). Time–frequency analysis was proposed as a complementary tool for the analysis of IE signals. The test records were analyzed by a time–frequency analysis method and are presented in a two-dimensional time–frequency plane. The advantages of using a time–frequency technique over a spectral analysis are described. Finally, the debonding assessments made on the basis of PSPA measurements were verified by ground truth data.

Mapping Voids, Debonding, Delaminations, Moisture, and Other Defects Behind or Within Tunnel Linings

Periodic monitoring of tunnel conditions and deterioration rates is the answer to determining the appropriate schedule of maintenance or rehabilitation activities to remedy structural problems that could lead to rapid deterioration and unexpected tunnel failures. The aggressive environmental conditions in which tunnels exist, as well as the need to keep tunnels open to traffic, make their inspection a challenge. Nondestructive testingmethods that are automated, quantitative, and rapid, and that provide complete coverage compared with conventional visual inspections, could solve this dilemma. This report presents the findings of the Strategic Highway Research Program 2 (SHRP 2) Renewal Project R06G—High-Speed Nondestructive Testing Methods for Mapping Voids, Debonding, Delaminations, Moisture, and Other Defects Behind or Within Tunnel Linings. The study was divided into two phases to (1) establish testing criteria and prioritize the techniques to be developed and evaluated under the project on the basis of tunnel operators’ requirements and (2) conduct the necessary technology development for those techniques recommended. In addition to conducting technology development, the project performed proof-of-concept and field testing. Beyond this report, the deliverables for this project include two products that will be published separately: 1) a user’s manual, which provides information on three NDT technologies for inspection of tunnels; and 2) a brief manual to the analysis software Tunnelcheck, which was developed under this project.

Nondestructive Detection of Delamination in Concrete Slabs: Multiple-Method Investigation

The delamination of concrete slabs is the separation along a plane roughly parallel to, and generally near, the surface. Corrosion-induced delamination is a common problem in old concrete bridge decks. If undetected, delaminations could expand, reach the surface, and result in spalling. Early detection of delamination is necessary for planning timely repairs that prevent costly deck replacement projects. Most bridge owners rely on routine visual and traditional surveys of bridge deck conditions. These surveys are highly subjective and can locate only large shallow delaminated zones. Several nondestructive testing (NDT) techniques have recently been employed for bridge deck evaluation to obtain more objective and comprehensive assessment. The reliability of applicable methods needs to be established before a greater role for NDT in routine inspections can be encouraged. This paper presents a validation study aimed at evaluating the effectiveness of three NDT techniques, namely impact echo, ultrasound (US) echo, and US linear array, in detection of delamination. This study is unique because the subject test specimens were deteriorated bridge deck segments preserved from the demolition of a prestressed box girder bridge. The results of the tests conducted on one of the specimens are presented and discussed here: impact echo provided satisfactory overall assessment, but the individual results were often difficult to interpret; US echo detected deep delaminations but not shallow ones; and US linear array located the extent of deep delaminations and provided indications of shallow ones.

Detection of Delamination in Concrete Bridge Decks by Joint Amplitude and Phase Analysis of Ultrasonic Array Measurements

AbstractThe accuracy and precision of low-frequency (center frequency of approximately 55 kHz) ultrasonic testing for detection and characterization of delamination in concrete bridge decks were evaluated. A multiprobe ultrasonic testing system (with horizontally polarized shear-wave transducers) was used to detect built-in delamination defects of various size, depth, and severity (i.e., thickness) in a test specimen—a 6.1 m×2.4 m×216 mm (20 ft×8 ft×8.5 in.) reinforced concrete slab-built to simulate a concrete bridge deck. The collected data sets were reconstructed applying synthetic aperture focusing technique (SAFT). The reconstructed measurement results were then used to assess the condition of the concrete slab at individual points [point-by-point data collection and two-dimensional (2D) reconstruction] as well as along lines, where data were collected at smaller steps and reconstructed in a three-dimensional (3D) format. The local-phase information was also calculated, superimposed on the reconstruc...

APPLICATION OF WAVELETS IN DETECTION OF CAVITIES UNDER PAVEMENTS BY SURFACE WAVES

Application of wavelet transforms in the detection of underground shallow cavities is investigated. Wave propagation is simulated through a transient response analysis on an axisymmetric finite element model. Cavities in a homogeneous half-space and a pavement system of a variety of shapes and embedment depths are considered. The continuous wavelet transform is introduced as a new tool for cavity detection. Effects of different types of cavities on power spectral surfaces (power spectral amplitudes versus frequency and receiver location) and Gaussian wavelet time-frequency maps (wavelet transform coefficients versus time and frequency) are studied. Results show strong energy concentration in power spectral surfaces right in front of a cavity in certain frequency bands. Time and frequency signatures of waves reflected from near and far faces of the cavity can be clearly observed in the wavelet time-frequency maps. These observations are used to locate and estimate the size of the cavity. It is demonstrated that the wavelet transform is a promising analysis tool for cavity detection and characterization.