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.

Civil and structural engineering consultants engaged in quality control or investigations of hardened concrete need a comprehensive resource that explains the methods of determining strength and other performance characteristics. Handbook on Nondestructive Testing of Concrete, Second Edition answers this demand by providing a thorough analys

Characterization of defect is one of the important objectives of nondestructive evaluation (NDE) for condition assessment of structures. Among many other NDE techniques, ultrasonic methods play a prominent role in the both quantitative and qualitative assessment of discontinuities in reinforced cementitious materials. Due to the heterogeneous nature of concrete, ultrasonic waves are highly scattered and attenuated, leading to the difficulty of concrete inspection using conventional ultrasonic techniques, including those that work well on relatively homogeneous materials such as metals. This thesis presents an advanced method for sizing and imaging of defects in reinforced cementitious materials. A two-dimensional, three-phase composite model of concrete is proposed to study the propagation and interaction behaviors of ultrasonic waves in concrete structures, and to gain a knowledge about wave diffraction with multiple cylindrical obstacles. The response of the modeled concrete structure to an incident ultrasonic pulse input signal (pulsed ultrasonic P-wave) is analytically investigated and simulated. A characteristic profile of the defect sizing as a function of focal depth is formulated via the synthetic focusing technique. A defect sizing parameter, called characteristic width, is obtained empirically to represent the defect sizing information for the concrete. Conventional 2-D ultrasonic B-scan imaging, for example, by migration, may introduce artifacts. In this thesis, the fundamental theory for synthetic aperture beam-forming through synthetic steering and focusing of array transducers is investigated. It is possible to achieve high spatial and temporal resolution ultrasonic image free of artifacts. A time-frequency signal processing and image reconstruction algorithm are also studied. The proposed defect sizing and imaging methodology is tested with numerically simulated ultrasonic waveform signals based on the mechanical properties of a custom-made concrete specimen. Experimental works confirm the feasibility of defect sizing and imaging of the method. With the knowledge about the concrete structures being tested this method may provide a useful tool for ultrasonic NDE application to reinforced cementitious materials.

Engineers have a range of sophisticated techniques at their disposal to evaluate the condition of reinforced concrete structures and non-destructive evaluation plays a key part in assessing and prioritising where money should be spent on repair or replacement of structurally deficient reinforced concrete structures. Non-destructive evaluation of reinforced concrete structures, Volume 2: Non-destructive testing methods reviews the latest non-destructive testing techniques for reinforced concrete structures and how they are used. Part one discusses planning and implementing non-destructive testing of reinforced concrete structures with chapters on non-destructive testing methods for building diagnosis, development of automated NDE systems, structural health monitoring systems and data fusion. Part two reviews individual non-destructive testing techniques including wireless monitoring, electromagnetic and acoustic-elastic waves, laser-induced breakdown spectroscopy, acoustic emission evaluation, magnetic flux leakage, electrical resistivity, capacimetry, measuring the corrosion rate (polarization resistance) and the corrosion potential of reinforced concrete structures, ground penetrating radar, radar tomography, active thermography, nuclear magnetic resonance imaging, stress wave propagation, impact-echo, surface and guided wave techniques and ultrasonics. Part three covers case studies including inspection of concrete retaining walls using ground penetrating radar, acoustic emission and impact echo techniques and using ground penetrating radar to assess an eight-span post-tensioned viaduct. With its distinguished editor and international team of contributors, Non-destructive evaluation of reinforced concrete structures, Volume 2: Non-destructive testing methods is a standard reference for civil and structural engineers as well as those concerned with making decisions regarding the safety of reinforced concrete structures. Reviews the latest non-destructive testing (NDT) techniques and how they are used in practice Explores the process of planning a non-destructive program features strategies for the application of NDT testing A specific section outlines significant advances in individual NDT techniques and features wireless monitoring and electromagnetic and acoustic-elastic wave technology

Non-destructive methods for materials testing are being increasingly used in testing concrete structures. In the construction industry, their use has resulted in improvements in the quality of concrete products and structures. It is no longer possible to rely solely on the traditional methods of quality control, and progressive, non-destructive methods must be applied in modern quality-control practice. This new approach in the field of non-destructive testing of concrete structures requires that new parameters be introduced for their verification and evaluation with regard to concrete strength, and for the solution of problems related to the use of combined multiparameter non-destructive methods. The present work provides a comprehensive overview on the solutions available for problems encountered in the non-destructive testing of concrete. Including the use of original combined ultrasonic-pulse methods developed by the author for testing concrete strength. Special attention is given to specific issues of testing in concrete structures and members by means of the combined and one-parameter methods and to the interpretation of the measurement results.