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Experimental Investigation of Impact-Echo Method for Concrete Slab Thickness Measurement
Popovics John S.,Cetrangolo Gonzalo P.,Jackson Nicole D. The Korean Society for Nondestructive Testing 2006 한국비파괴검사학회지 Vol.26 No.6
Accurate estimates of in place thickness of early age (3 to 28 days after casting) concrete pavements are needed, where a thickness accuracy of ${\pm}6mm$ is desired. The impact-echo method is a standardized non-destructive technique that has been applied for this task. However, the ability of impact-echo to achieve this precision goal is affected by Vp (measured) and ${\beta}$ (assumed) values that are applied in the computation. A deeper understanding of the effects of these parameters on the accuracy of impact-echo should allow the technique to be improved to meet the desired accuracy goal. In this paper, the results of experimental tests carried out on a range of concrete slabs are reported. Impact-echo thickness estimation errors caused by material property gradients and sensor type are identified. Correction factors to the standard analysis method are proposed to correct the identified errors and to increase the accuracy of the standard method. Results show that improved accuracy can be obtained in the field by applying these recommendations with the standard impact-echo method.
Air-coupled ultrasonic tomography of solids: 1 Fundamental development
Kerry S. Hall,John S. Popovics 국제구조공학회 2016 Smart Structures and Systems, An International Jou Vol.17 No.1
Ultrasonic tomography is a powerful tool for identifying defects within an object or structure. But practical application of ultrasonic tomography to solids is often limited by time consuming transducer coupling. Air-coupled ultrasonic measurements may eliminate the coupling problem and allow for more rapid data collection and tomographic image construction. This research aims to integrate recent developments in air-coupled ultrasonic measurements with current tomography reconstruction routines to improve testing capability. The goal is to identify low velocity inclusions (air-filled voids and notches) within solids using constructed velocity images. Finite element analysis is used to simulate the experiment in order to determine efficient data collection schemes. Comparable air-coupled ultrasonic signals are then collected through homogeneous and isotropic solid (PVC polymer) samples. Volumetric (void) and planar (notch) inclusions within the samples are identified in the constructed velocity tomograms for a variety of transducer configurations. Although there is some distortion of the inclusions, the experimentally obtained tomograms accurately indicate their size and location. Reconstruction error values, defined as misidentification of the inclusion size and position, were in the range of 1.5-1.7%. Part 2 of this paper set will describe the application of this imaging technique to concrete that contains inclusions.
Nondestructive Contactless Sensing of Concrete Structures using Air-coupled Sensors
Sung Woo Shin,Kerry S. Hall,John S. Popovics 한국안전학회(구-한국산업안전학회) 2008 International Journal of Safety Vol.7 No.2
Recent developments in contactless, air-coupled sensing of seismic and ultrasonic waves in concrete structures are presented. Contactless sensing allows for rapid, efficient and consistent data collection over a large volume of material. Two inspection applications are discussed: air-coupled impact-echo scanning of concrete structures using seismically generated waves, and air-coupled imaging of internal damages in concrete using ultrasonic tomography. The first application aims to locate and characterize shallow delamination defects within concrete bridge decks. Impact-echo method is applied to scan defected concrete slabs using air coupled sensors. Next, efforts to apply air-coupled ultrasonic tomography to concrete damage imaging are discussed. Preliminary results are presented for air-coupled ultrasonic tomography applied to solid elements to locate internal defects. The results demonstrate that, with continued development, air-coupled ultrasonic tomography may provide improved evaluation of unseen material defects within structures.
Nondestructive Contactless Sensing of Concrete Structures using Air-coupled Sensors
Shin, Sung-Woo,Hall, Kerry S.,Popovics, John S. The Korean Society of Safety 2008 International Journal of Safety Vol.7 No.2
Recent developments in contactless, air-coupled sensing of seismic and ultrasonic waves in concrete structures are presented. Contactless sensing allows for rapid, efficient and consistent data collection over a large volume of material. Two inspection applications are discussed: air-coupled impact-echo scanning of concrete structures using seismically generated waves, and air-coupled imaging of internal damages in concrete using ultrasonic tomography. The first application aims to locate and characterize shallow delamination defects within concrete bridge decks. Impact-echo method is applied to scan defected concrete slabs using air coupled sensors. Next, efforts to apply air-coupled ultrasonic tomography to concrete damage imaging are discussed. Preliminary results are presented for air-coupled ultrasonic tomography applied to solid elements to locate internal defects. The results demonstrate that, with continued development, air-coupled ultrasonic tomography may provide improved evaluation of unseen material defects within structures.
신성우(Shin Sung-Woo),윤정방(Yun Chung-Bang),송원준(Song Won-Joon),John S. Popovics 한국구조물진단유지관리학회 2005 한국구조물진단학회 학술발표회논문집 Vol.9 No.2
Surface wave velocity measurement technique considering concrete heterogeneity is developed in this study. The technique proposed in this study is distinct from that of earlier researchers. A major difference comes from the determination of time of flight using wavelet coefficients. It is, in previous researches, determined by the cross-correlation technique, the difference in the phase spectra, or the time difference between the first significant sharp peaks in the time domain signals of each receiver. An experimental study isperformed to demonstrate the differences and effectiveness of the proposed technique in comparison with the conventional techniques. Results shows that the proposed method is less sensitive for the concrete heterogeneity than the conventional technique and thus it can be effectively used for determine the group velocity of concrete.