Detection and Characterization of Disbond Damage at Steel-Concrete Interfaces Using Attenuation Characteristics of Guided Waves

This paper presents a frequency-wavenumber (f-k) domain signal processing approach for guided plate wave data. The guided waves propagate in a steel plate bonded to concrete substrate, and the analysis aims to characterize the steel-concrete interface. The modal solutions of guided waves in well-bonded, partially bonded, and dis-bonded interface cases are obtained using the Global Matrix technique. The analytical solutions demonstrate that the attenuation characteristics of the fundamental symmetric (S0) guided wave mode in the steel plate are sensitive to the steel-concrete interface bond condition. The attenuation behavior of the S0 mode are captured and extracted from the complete guided wave signal set obtained by air-coupled ultrasonic tests. Using f-k domain signal analysis, the fundamental anti-symmetric (A0) mode is suppressed and the S0 mode is isolated. The S0 mode attenuation across the scanned spatial points is then estimated and used to characterize the bond condition of the steel-concrete interface. This signal processing approach is verified by a series of numerical simulation and laboratory-scale experiments. The results demonstrate that interface bond condition can be successfully characterized using the proposed f-k domain signal analysis approach

A New Approach for the Analysis of Impact-Echo Data

The recently developed impact-echo (IE) method, which utilizes an impact and subsequent displacement monitoring of the concrete surface, appears promising for the inspection of concrete structures. IE has been shown to be particularly suitable for void, delamination, and cracking detection in hardened concrete structures including bridge decks since deep penetration into the structure and one-sided accessibility are obtained. For this method to be reliable, however, accurate measurements of peak frequencies in the magnitude spectrum of the frequency domain must be made. In addition, the interpretation of confusing spectrums may be required. The first part of this paper reviews the existing impact echo technique, including typical signal generation and capture possibilities as well as the accepted signal processing. Next, an alternative approach to signal processing is developed; this approach is based on a brief literature review and laboratory experiments. It is proposed that this approach, based on the spacing of peaks in the magnitude spectrum may reduce the uncertainty of impact echo signal analysis

Study of Flexural Stress-induced Surface Wave Velocity Variations in Concrete

This investigation studies the behavior of surface wave velocity in concrete specimens subjected to low levels of compressive and tensile stress in beams from applied flexural loads. Beam specimens are loaded in a 4-point-load bending configuration, generating uniaxial compression and tension stress fields at the beams’ top and bottom surfaces, respectively. Surface waves are generated through contactless air-coupled transducers and received through contact accelerometers. Results show a clear distinction in responses from compression and tension zones, where velocity increases in the former and decreases in the latter, with increasing load levels. These trends agree with existing acoustoelastic literature. Surface wave velocity tends to decrease more under tension than it tends to increase under compression, for equal load levels. It is observed that even at low stress levels, surface wave velocity is affected by acoustoelastic effects, coupled with plastic effects (stress-induced damage) and viscoelastic effects (creep and relaxation). The acoustoelastic effect is isolated by means of considering the Kaiser effect and by experimentally mitigating the viscoelastic effects of concrete. Results of this ongoing investigation contribute to the overall knowledge of the acoustoelastic behavior of concrete. Applications of this knowledge may include structural health monitoring of members under flexural loads, improved high order modelling of materials, and validation of results seen in dynamic acoustoelasticity testing

Comparison of Synthetic Aperture Radar and Impact-Echo Imaging for Detecting Delamination in Concrete

In this paper we evaluate the utility of microwave and mechanical wave nondestructive testing techniques to detect delamination in reinforced concrete bridge deck mock-up samples. The mechanical wave tests comprise air-coupled impact-echo measurements, while the microwave measurements comprise three-dimensional synthetic aperture radar imaging using wideband reflectometery in the frequency range of 1-4 GHz. The results of these investigations are presented in terms of images that are generated from these data. Based on a comparison of the results, we show that the two methods are complementary, in that provide distinct capabilities for defect detection. More specifically, the former approach is unable to detect depth of a delaminated region, while the latter may provide this information. Therefore, the two methods may be used in a complementary fashion (i.e., data fusion) to give more comprehensive information about the 3D location of delamination

Air-coupled Ultrasonic Tomography for Internal Damage of Full-Scale Reinforced Concrete Moment Frame Components Subjected to Seismic Loadings

Full-scale reinforced concrete (RC) components are imaged using ultrasonic tomography before, during, and after simulated earthquake loads, up to a drift level of 1%, are applied. A total of five RC moment frame components, including three columns and two slab-beam-column sub-assemblages, are subjected to three different seismic loading protocols. Two advanced structural materials, ultra-high-performance fiber-reinforced concrete (UHP-FRC) and high-performance fiber-reinforced concrete (HPFRC) are used in one of the columns and one of the slab-beam- column sub-assemblages, respectively. The components contain embedded strain gauges that are used to establish accumulated damage at certain locations. Our hybrid air-coupled ultrasonic system is used to collect a large volume of through thickness ultrasonic data across the plastic hinge zone region of the components. The ultrasonic data sets are used to back-calculate wave velocity tomograms across the cross-section at the plastic hinge regions for each component. A comparison of ultrasonic and strain gauge data shows the great potential of using ultrasonic tomography to evaluate damage progression of RC structures both at global and local levels. The results also confirm that UHP-FRC and HPFRC behave differently from conventional reinforced concrete

Measurement of XUV-absorption spectra of ZnS radiatively heated foils

Time-resolved absorption of zinc sulfide (ZnS) and aluminum in the XUV-range has been measured. Thin foils in conditions close to local thermodynamic equilibrium were heated by radiation from laser-irradiated gold spherical cavities. Analysis of the aluminum foil radiative hydrodynamic expansion, based on the detailed atomic calculations of its absorption spectra, showed that the cavity emitted flux that heated the absorption foils corresponds to a radiation temperature in the range 55 60 eV. Comparison of the ZnS absorption spectra with calculations based on a superconfiguration approach identified the presence of species Zn6+ - Zn8+ and S5+ - S6+. Based on the validation of the radiative source simulations, experimental spectra were then compared to calculations performed by post-processing the radiative hydrodynamic simulations of ZnS. Satisfying agreement is found when temperature gradients are accounted for

Surface-Wave Based Model for Estimation of Discontinuity Depth in Concrete

In this paper, we propose an accurate and practical model for the estimation of surface-breaking discontinuity (i.e., crack) depth in concrete through quantitative characterization of surface-wave transmission across the discontinuity. The effects of three different mixture types (mortar, normal strength concrete, and high strength concrete) and four different simulated crack depths on surface-wave transmission were examined through experiments carried out on lab-scale concrete specimens. The crack depth estimation model is based on a surface-wave spectral energy approach that is capable of taking into account a wide range of wave frequencies. The accuracy of the proposed crack depth estimation model is validated by root mean square error analysis of data from repeated spectral energy transmission ratio measurements for each specimen