Herbert Wiggenhauser

Comparison of pulse-echo methods for testing concrete

Abstract Pulse-echo methods (radar, impact-echo, ultrasonic impulse-echo) and simulation of wave propagation are applied for testing concrete speciments with metal ducts. The results of nondestructive testing of the same specimens by nine workgroups are described and compared. The research aims for the experiments are thickness measurement, location of a metal duct and of voided regions inside the duct. The results show the remarkable progress achieved in the past few years: the thickness and location of a duct could be measured for one specimen with great precision. In some cases voided regions in the duct could be located.

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.

Detection of shallow voids in concrete structures with impulse thermography and radar

Abstract New thermography systems enable the application of active investigation techniques, i.e. the observation of the cooling down process after heating the surface of a structure under investigation. Defects like voids in concrete having a different thermal diffusivity in comparison to the bulk material are visualised by different surface temperatures. The differences between temperature transient curves above sound regions and above inhomogeneities are expected to include information about the defect parameters. Experimental investigations with impulse thermography and radar on a concrete test specimen containing voids were analysed. Radar was used to determine the depth of the voids. The influence of size and depth of the voids on the temperature transient curves was studied for different heating times. The transient curves were also fitted with a simple semi-empirical model.

Ultrasonic imaging of concrete members using an array system

The use of an ultrasonic array system is described, which can be used combined with 3D reconstruction calculations. In this way ultrasonic reflection and backscatter from the inside of concrete members can be imaged and interpreted. The application of the system is demonstrated for two examples: measuring the concrete cover of utility pipes in a tunnel and the examination of transversal ducts in a bridge plate.

Transient thermography for structural investigation of concrete and composites in the near surface region

The cooling down process of building structures after heating up with an external radiation source was analysed to detect voids inside and below the surface of a concrete test specimen containing voids with different sizes at various depth or covered with carbon fibre reinforcing laminates. These experimental investigations were compared to the results of simulations performed with a finite difference program.

Non-Destructive Testing in Civil Engineering

Preface to Special Collection of coutributions to the International Symposium NDT-CE 2015 in Berlin/ Germany.

LIBS for non-destructive testing of element distributions on surfaces

Abstract A laser-based technique for the quasi non-destructive evaluation of surfaces of building materials is presented. Laser-induced breakdown spectroscopy (LIBS) is an analytical tool to determine the chemical composition of laser evaporated material. After the material has been vaporized by the high energy laser pulse the elements emit their specific fluorescence. This radiation is used to identify the elements in the evaporated material by spectroscopic methods. The mass of the evaporated material is of the order of micrograms; this means LIBS is a quasi non-destructive method for building applications. The main advantages of LIBS are the direct measurement without any preparation and the possibility to measure on site and to obtain on-line results. LIBS is a well-known technique which has been successfully applied in the areas of material testing, medicine and industrial process control. This article reports on the progress of LIBS applications for building materials by the use of some examples: identification and analysis of the main components of concrete; determination of salt concentrations in building materials; and measuring the relative element composition to a depth of up to 10 mm with high geometrical resolution.

A study of concrete hydration and dielectric relaxation mechanism using ground penetrating radar and short-time Fourier transform

Ground penetrating radar (GPR) was used to characterize the frequency-dependent dielectric relaxation phenomena in ordinary Portland cement (OPC) hydration in concrete changing from fresh to hardened state. The study was experimented by measuring the changes of GPR A-scan waveforms over a period of 90 days, and processed the waveforms with short-time Fourier transform (STFT) in joint time-frequency analysis (JTFA) domain rather than a conventional time or frequency domain alone. The signals of the direct wave traveled at the concrete surface and the reflected wave from an embedded steel bar were transformed with STFT, in which the changes of peak frequency over ages were tracked. The peak frequencies were found to increase with ages and the patterns were found to match closely with primarily the well-known OPC hydration process and secondarily, the evaporation effect. The close match is contributed to the simultaneous effects converting free to bound water over time, on both conventional OPC hydration and dielectric relaxation mechanisms.

Non-destructive investigation of sluices using radar and ultrasonic impulse echo

Radar and ultrasonic impulse echo have been successfully applied for the assessment of two almost 100 year old sluices. The interior condition of the side walls has been investigated with radar enabling the detection of detachments of the faced brickwork as well as the determination of moisture content. With ultrasonic impulse echo working joints were found in the concrete slab of the sluice heads. The results of these investigations gathered comparative data to reduce the number of cores which had to be taken.

Measurement of Accelerated Steel Corrosion in Concrete Using Ground-Penetrating Radar and a Modified Half-Cell Potential Method

A new approach is presented to evaluate corrosion of steel bars in concrete by 1.5- and 2.6-GHz ground-penetrating radar (GPR) and a modified half-cell potential method. Changes in time-lapsed travel times, amplitudes, and peak frequencies that are associated with short-time Fourier transform spectrograms of the bar reflections were continuously measured. The year-long corrosion process of the reinforcement bar rapidly accelerated within a few days by impressing direct current across a pair of embedded reinforcement bars, which served as the anode and cathode. When corrosion started, the travel times, amplitudes, and frequency spectra of the bar reflection changed. The results were analyzed by dividing the material’s response into three phases (NaCl contamination, depassivation, and corrosion). The writers attribute the phenomena of the first two phases to the ionic conduction and interfacial polarization effect, described in the low-frequency regime of complex dielectric permittivity outlined in the Maxwell-Wagner effect. The remaining phase corresponds with the appearance of large and multiple interfaces among steel, concrete, corrosion product, and cracks, in addition to the upward movement of the corrosion product to the concrete surface that intercepts wider radar footprints. The findings, based on time lapse measurements, provide a basis to further apply the GPR technique to spatial measurements in laboratory and field studies.