Mechanical waves provide information about the stiffness and the condition of a medium; thus, changes in medium conditions can be inferred from changes in wave velocity and attenuation. Non-destructive testing (NDT) methods based on ultrasonic waves are often more economical, practical and faster than destructive testing. Multichannel analysis of surface waves (MASW) is a well-established surface wave method used for determination of the shear-wave profile of layered medium. The MASW test configuration is also applicable to assess the condition of concrete elements using appropriate frequency range. Both attenuation and dispersion of ultrasonic waves can be evaluated by this technique. In ultrasonic testing, the characterization of a medium requires the precise measurement of its response to ultrasonic pulses to infer the presence of defects and boundary conditions. However, any ultrasonic transducer attached to a surface affects the measured response; especially at high frequencies. On the other hand, ultrasonic transducers available for engineering application are mostly used to measure wave velocities (travel time method). Therefore, these transducers do not have a flat response in the required frequency range. Moreover, in the case of full-waveform methods, the recorded signals should be normalized with respect to the transfer functions of the transducers to obtain the real response of the tested specimen. The main objective of this research is to establish a comprehensive methodology based on surface wave characteristics (velocity, attenuation and dispersion) for condition assessment of cemented materials with irregular defects. To achieve the major objective, the MASW test configuration is implemented in the ultrasonic frequency range. The measured signals are subjected to various signal processing techniques to extract accurate information. In addition, a calibration procedure is conducted to determine the frequency response functions (FRF) of the piezoelectric accelerometers outside their nominal frequency range. This calibration is performed using a high-frequency laser vibrometer. This research includes three main studies. The first study introduces the calibration approach to measure the FRFs of the accelerometers outside of their flat frequency range. The calibrated accelerometers are then used to perform MASW tests on a cemented-sand medium. The original signals and the corrected ones by eliminating the effect of the FRFs are used to determine material damping of the medium. Although, the damping ratios obtained from different accelerometers are not same, the values from the corrected signals are found closer to the characteristic damping value compared to those from the uncorrected signals. The second study investigates the sensitivity of Rayleigh wave velocity, attenuation coefficient, material damping and dispersion in phase velocity to evaluate the sensitivity of these characteristics to the damage quantity in a medium. The soft cemented-sand medium is preferred as the test specimen so that well-defined shaped defects could be created in the medium. MASW test configuration is implemented on the medium for different cases of defect depth. The recorded signals are processed using different signal processing techniques including Fourier and wavelet transforms and empirical mode decomposition to determine the surface wave characteristics accurately. A new index, 'dispersion index', is introduced which quantifies the defect based on the dispersive behaviour. All surface wave characteristics are found capable of reflecting the damage quantity of the test medium at different sensitivity levels. In the final study, the condition assessment of six lab-scale concrete beams with different void percent is performed. The beam specimens involving Styrofoam pellets with different ratios are tested under ultrasonic and mechanical equipment. The assessment produce established in the second study with well-defined defects is pursed for the beams with irregular defects. Among the characteristics, attenuation, P and R-wave velocities and dispersion index are found as the promising characteristics for quantifying the defect volume.

Surface waves propagating in a medium provide information about the mechanical properties and condition of the material. Variations in the material condition can be inferred from changes in the surface wave characteristics. Multichannel analysis of surface waves (MASW) is a well-established surface wave method used for determination of the shear-wave profile of the soil layers near the surface. The MASW test configuration is also applicable to assess the condition of construction materials using appropriate frequency range. Previous studies on the detection of surface-breaking cracks in concrete elements, using the dispersion and attenuation of ultrasonic waves, were successful; however, a complete damage assessment of the whole element was not in the scope of these studies. In this study, different wave characteristics, such as Rayleigh wave velocity, wave attenuation, and phase velocity dispersion, are investigated to evaluate their sensitivity to the damage in a medium. The condition of a test specimen, which is a half-space medium made of cement and sand, is evaluated using ultrasonic transducers for different damage cases. The recorded signals are processed using the Fourier and wavelet transforms to determine the surface wave characteristics. A new dispersion index (DI) is introduced, which represents the global correlation between the dispersion of phase velocity and damage level. All features are found to be capable of reflecting the damage in the test medium with different levels of sensitivity. Among the investigated parameters, the proposed dispersion index shows high sensitivity and linear correlation with the damage.

Reinforced concrete is one of the materials most used in civil infrastructure, and the expected service life is generally for several decades. However, as any other material, concrete performance is affected by environmental conditions, the normal use of the structure, ageing and extreme load events. All of these factors affect the elements performance and can induce damage. Since all infrastructure components deteriorate over time, it is needed to assess their actual condition. Moreover, to implement adequate corrective measures it is needed to first detect damage and quantify its extent. There are different methods that may be used to inspect concrete elements, and the selection of the adequate technique depends on the property of interest and the available resources. Among the available inspection methods, the nondestructive techniques (NDT) are those used to detect defects, to estimate the material properties or to assess the integrity of components that do not affect the elements under evaluation. Every inspection technique has advantages and disadvantages; and consequently, the current trend is to use a combination of methods. Even though several nondestructive methods are commercially available, currently there is no comprehensive method to evaluate concrete columns. Taking in consideration these aspects, the main objective of this research was to develop a new nondestructive methodology and testing device that would allow inspecting concrete columns in a fast and reliable manner, without affecting their future performance. The proposed methodology relies on ultrasonic tests. The condition evaluation is based on measurements of wave velocity and wave attenuation because it is known that the attenuation is more sensitive to damage than the velocity. However, wave attenuation is generally not used in site evaluations because is very difficult to ensure consistent measurements in the field. To overcome this limitation, a new ultrasonic testing device was developed and tested. To verify the applicability of the methodology, reinforced and unreinforced concrete samples were tested in the laboratory, and a sample of in-service reinforced concrete columns was also evaluated. The main contributions of the research presented in this thesis are: The construction of a new ultrasonic field testing device to test structural elements with circular cross section. The evaluation of a new methodology to evaluate concrete elements based on statistical indexes computed from wave velocity and wave attenuation by testing a sample of in-service columns. The new methodology allows detecting damage at earlier stages which would allow implementing opportune corrective measures. The proposal and evaluation of an alternative testing procedure to evaluate freeze/thaw damage in concrete specimens based on wave attenuation measurements. The appraisal of a new procedure to monitor progressive damage in concrete elements using surface wave measurements. The evaluation of alternative signal processing techniques of the signals obtained from the surface wave testing to facilitate the analysis of the results.

The non-destructive evaluation of civil engineering structures in reinforced concrete is becoming an increasingly important issue in this field of engineering. This book proposes innovative ways to deal with this problem, through the characterization of concrete durability indicators by the use of non-destructive techniques. It presents the description of the various non-destructive techniques and their combination for the evaluation of indicators. The processing of data issued from the combination of NDE methods is also illustrated through examples of data fusion methods. The identification of conversion models linking observables, obtained from non-destructive measurements, to concrete durability indicators, as well as the consideration of different sources of variability in the assessment process, are also described. An analysis of in situ applications is carried out in order to highlight the practical aspects of the methodology. At the end of the book the authors provide a methodological guide detailing the proposed non-destructive evaluation methodology of concrete indicators. Presents the latest developments performed in the community of NDT on different aspects Provides a methodology developed in laboratory and transferred onsite for the evaluation of concrete properties which are not usually addressed by NDT methods Includes the use of data fusion for merging the measurements provided by several NDT methods Includes examples of current and potential applications

Condition assessment and characterization of materials and structures by means of nondestructive testing (NDT) methods is a priority need around the world to meet the challenges associated with the durability, maintenance, rehabilitation, retrofitting, renewal and health monitoring of new and existing infrastructures including historic monuments. Numerous NDT methods that make use of certain components of the electromagnetic and acoustic spectrum are currently in use to this effect with various levels of success and there is an intensive worldwide research effort aimed at improving the existing methods and developing new ones. The knowledge and information compiled in this book captures the current state of the art in NDT methods and their application to civil and other engineering materials and structures. Critical reviews and advanced interdisciplinary discussions by world-renowned researchers point to the capabilities and limitations of the currently used NDT methods and shed light on current and future research directions to overcome the challenges in their development and practical use. In this respect, the contents of this book will equally benefit practicing engineers and researchers who take part in characterization, assessment and health monitoring of materials and structures.

The Special Issue “Non-Destructive Testing of Structures” has been proposed to present the recent developments in the field of the diagnostics of structural materials and components in civil and mechanical engineering. The papers highlighted in this editorial concern various aspects of non-invasive diagnostics, including such topics as the condition assessments of civil and mechanical structures and the connections of structural elements, the inspection of cultural heritage monuments, the testing of structural materials, structural health monitoring systems, the integration of non-destructive testing methods, advanced signal processing for the non-destructive testing of structures (NDT), damage detection and damage imaging, as well as modeling and numerical analyses for supporting structural health monitoring (SHM) systems.

This book gives information on non destructive techniques for assessment of concrete structures. It synthesizes the best of international knowledge about what techniques can be used for assessing material properties (strength) and structural properties (geometry, defects...). It describes how the techniques can be used so as to answer a series of usual questions, highlighting their capabilities and limits, and providing advices for a better use of techniques. It also focuses on possible combinations of techniques so as to improve the assessment. It is based on many illustrative examples and give in each case references to standards and guidelines.