Modern NDT Techniques in Diagnostics of Transport Infrastructure Concrete Structures

Transcription

1 International Workshop on SMART MATERIALS, STRUCTURES NDT in Canada 2013Conference & NDT for the Energy Industry October 7-10, 2013 Calgary, Alberta, CANADA Modern NDT Techniques in Diagnostics of Transport Infrastructure Concrete Structures Jan Bień 1, Jerzy Hoła 2, Łukasz Sadowski 3 1 Institute of Civil Engineering, Wroclaw University of Technology, jan.bien@pwr.wroc.pl 2 Institute of Building Engineering, Wroclaw University of Technology, jerzy.hola@pwr.wroc.pl 3 Institute of Building Engineering, Wroclaw University of Technology, lukasz.sadowski@pwr.wroc.pl ABSTRACT In recent years intensive development of the Non-Destructive Testing (NDT) s as applied to the assessment of the condition of transport infrastructure concrete structures (bridges, roads, railways, tunnels, etc.) has been observed. In this paper, classifications of the s, based on various criteria, are proposed and discussed. Special attention is paid to advanced acoustic s as applied to the identification of delaminated areas, the detection of internal material defects, the discovery of crack parameters and the precise measurement of structural element thickness, the location of reinforcement, prestressing wires, etc. This paper focuses on ultrasonic tomography, the impulse-response and the impact-echo. The s are illustrated with practical examples, including descriptions of the equipment, the testing procedures, the data acquisition and recording systems, and the numerical data processing procedures based on comprehensive algorithms. The range and conditions of the application of the considered NDT s in the diagnostics of transport infrastructure concrete structures are proposed and discussed. Key words: transport infrastructure structures, acoustic s, ultrasonic tomography, impulse-response, impact-echo. INTRODUCTION The methods used to diagnose transport network structures can be divided into destructive, semi-nondestructive and non-destructive (fig. 1). Destructive tests can be applied to samples and natural scale elements. Both the former and the latter are destroyed in the course of the test [1-3] whereby the number of destructive tests on natural scale elements is most often limited to some representative elements. Semi-nondestructive tests are also applied to samples and natural scale elements and structures. Usually the surface of the tested element is locally breached (and

2 so needs repairing), which leads to the local loss of the element s functional properties. No such breaching occurs when natural scale members and structures are non-destructively tested. Moreover, the same members and structures can be subjected to non-destructive tests repeatedly and at different times, whereby non-destructive s are useful in diagnosing building structures both during their erection and in the many years of their service [1-3]. It is also important that various NDT s can be applied in the same area of the tested structure and results can be compared in the condition assessment process. Fig. 1: General division of methods useful in diagnosing transport infrastructure structures. Figure 2 shows a detailed classification of non-destructive s which can be used to diagnose transport infrastructure concrete structures. Acoustic s form a major group of non-destructive s. Recently intensive development of acoustic s has been observed. The latest of the s are concisely described further in this paper. Non-destructive s useful in diagnosing transport infrastructure concrete structures Acoustic s Electrochemical s Moisture content estimation s Laser scanning s Ultrasonic Potentiometric Chemical Laser triangulation Echo Resistance Physical Optical Impact-echo Linear polarization Laser scanner Impulse-response Penetration Ultrasonic tomography Radar Seismic Acoustic emission Resonance Fig. 2: Non-destructive s useful in diagnosing transport infrastructure concrete structures.

3 NON-DESTRUCTIVE ACOUSTIC TECHNIQUES Non-destructive acoustic s are used to test elements made of concrete in order to assess interlayer delamination, the thickness of elements accessible from one side only, defects not visible on the surface, the depth of cracks in elements and the distribution of reinforcement in reinforced concrete members. The modern non-destructive s useful in diagnosing transport network structures, i.e. the impulse-response, the impact-echo and ultrasonic tomography, are graphically presented and briefly described in the table 1. For each of the considered modern acoustic non-destructive s the following information is presented: name and short description of the, schematic drawing of arrangement of the testing equipment and photos illustrating practical application of the testing tools, list of parameters determined during the test and examples of the graphical form of test results. The testing methods shown in table 1 can be applied in the process of condition assessment of various concrete structures belonging to the transportation network, like bridges made of reinforced or prestressed concrete, retaining walls, concrete road pavements, etc. Tab. 1: Comparison of modern acoustic non-destructive s [5-25]. Technique name and description Schematic of test setup and view of equipment Registered parameters and exemplary test results The impulse-response consists in exciting an elastic ultrasonic wave in a tested element by means of a rubber-tipped hammer. The frequency of the excited wave is in a range of Hz and the extent of excitation around the test point is about 1000 mm. This is suitable for the approximate location of areas in which defective concrete (honeycombing) zones may occur, to a depth of about 1500 mm. The impulse-response is suitable for the quick scanning of large concrete surfaces for defects, such as delamination, cracks and air voids, and assessing the adhesion between concrete layers. The values of the following parameters are registered: - average mobility N av, - stiffness K d, - mobility slope M p /N, - mobility times mobility slope N av M p /N, - voids index v. An exemplary map of average mobility N av : Nr kolumny 0,00-0,10 0,10-0,20 0,20-0,30 0,30-0,

4 Tab. 1: Comparison of modern acoustic non-destructive s [5-25] (cont.). Technique name and description The impact-echo consists in exciting an elastic wave having a frequency of 1-60 khz in the tested element, by striking its surface with an exciter in the form of a steel ball. The equipment includes a set of steel balls with different diameters. Specialist software enables the recording of the elastic wave propagating in the tested element, as an amplitude-time graph and the transformation of the latter into an amplitude-frequency spectrum by means of the Fourier transform. The impact-echo is suitable for testing concrete members and assessing: thickness at unilateral access, cable conduit injection effectiveness, surface crack depth, adhesion between concrete layers, delamination, cracks, inclusions and air voids. The ultrasonic tomography consists in exciting an elastic wave in the tested element by means of a multihead antenna made up of ultrasonic heads for receiving and processing signals. The heads generate 50 Hz ultrasonic pulses. The maximum range, in terms of the tested element thickness, amounts to 2500 mm. The can be used to test concrete elements in order to determine their thickness at unilateral access and to detect cracks, inclusions, air voids and other places which may be empty or filled with a liquid or a material whose density differs from that of the surrounding concrete. In the course of testing the tomograph antenna is shifted stepwise by a distance of 100 mm in the same direction in a 380 or 500 mm wide (depending on the antenna type) test band. The obtained results, in the form of images of the cross sections in each antenna position, are collected in a three-dimensional matrix table. Schematic of test setup and view of equipment Registered parameters and exemplary test results The values of the following parameters are registered: - transmitting pulse amplitude A, - frequency f D of an ultrasonic wave reflection from a defect, - frequency f T. of ultrasonic reflection from the bottom. An exemplary amplitudefrequency graph for an ultrasonic wave reflection from the bottom: Three images, i.e. B, C and D, in three mutually perpendicular directions are recorded: Exemplary image in direction B:

5 EXEMPLARY APPLICATIONS Two examples of the integrated simultaneous application of two of the non-destructive acoustic s presented in table 1 are provided below. The authors experience indicates that the two s when used in an integrated way complement each other and so can be highly useful for testing transport infrastructure. In the first example, the impulse-response and the impact-echo are used together for the nondestructive identification of delaminations in an extensive concrete floor topping in a multi-level garage. In the second example, the impulse-response and the impact-echo are supported by the optical and artificial neural networks in order to non-destructively estimate the pull-off adhesion of the concrete layers. Other examples of the use of the ultrasonic combined with the impulseresponse or the impact-echo were presented in [4, 12]. Non-destructive identification of delamination in concrete floor topping in multi-level garage A defective concrete floor topping, covering the area of 2000 m 2, in a multi-level car park building was tested using the impulse-response and the impact-echo combined [13]. After about one year of service, defects, such as cracks (fig. 3a) and rising of some field corners, appeared in the concrete floor topping. The concrete floor topping would curl under moving vehicles. In winter, water from melting snow carried in on the tires of cars would penetrate into the cracks. As cars drove onto the floor topping the water would be squeezed out and then would penetrate back into the cracks. This indicated that defective areas, where there was no cohesion between the top layer and the base layer, occurred in the floor. The aim of the tests was to locate the defective (lacking adhesion) areas. The non-destructive identification of delamination was carried out in two stages. In stage 1, tests were carried out using the impulse-response in order to roughly identify the concrete floor topping areas where there was no adhesion at the interface between the layers (fig. 3b) while in stage 2, tests were carried using the impact-echo in order to precisely identify the defective area, especially its boundaries (fig. 3c). The investigations proved the impulse-response and the impact-echo to be useful for identifying delamination in concrete floor topping covering a large surface area. As a result of the tests the areas were delamination occurred (the pull-off adhesion amounted there to zero) were identified. Moreover, a general investigation methodology was developed on the basis of a number of similar tests and published in [13]. This methodology deals with the assessment of the interlayer debonding in concrete floors, using the zero/one (no bond/bond) system. It is proper to note that using developed methodology it is not possible to determine the values of pull-off adhesion between the concrete layers.

6 a) b) c) Fig. 3: View of: a) crack in top layer of floor, b) fragment of tested floor with defective area roughly located using impulse-response where there was no adhesion at the interface between the layers, c) fragment of floor with delamination boundaries precisely determined using impact-echo [13]. Non-destructive estimation of pull-off adhesion of concrete layers Using the impulse-response and the impact-echo one can quite easily identify the areas where delamination occurs. But is rather difficult to non-destructively determine the values of pull-off adhesion between the concrete layers. In [25] an attempt was made to determine reliable correlations between each of the parameters and pull-off adhesion f b estimated by the pull-off method. But the obtained low values of determination coefficient R 2 indicated that this approach was not viable. However, such correlations can be determined when the investigations are supported with the optical and artificial neural networks as a results processing tool. This was demonstrated in [26-28] where the aim was the non-destructive identification of pull-off adhesion f b between the top layer and the base layer. This was achieved using the base layer surface roughness parameters estimated by the optical (fig. 4a) and the parameters estimated on the floor surface by the acoustic s mentioned above (figs 4b and c).

7 a) b) c) d) Fig. 4: Non-destructive estimation of pull-off adhesion: a) determination of base layer surface roughness by non-destructive optical, b) testing by impulse-response, c) testing by non-destructive impact-echo, d) testing by semi-nondestructive pull-off method. The parameters were determined in several hundred measuring places distributed on the surface of a model test specimen. Then cores were drilled in the top layer and pulled off from the base layer to determine pull-off adhesion f b (fig. 4d). The test results (the values of the parameters) were subjected to statistical analyses whereby a few parameters (see table 2) suitable to be used as input variables for the training and testing of an artificial neural network were selected. A proper structure and a training algorithm were adopted for the ANN. Tab. 2: Values of input variables used to train and test artificial neural network. Test point number Name of test method and parameter symbol Optical Impulse-response Impact-echo Pull-off method S a S q K d N av f T f b mm mm - m/s N - MPa

8 A unidirectional multilayer backpropagation ANN with the QUASI-NEWTON training algorithm, 10 hidden layer neurons and hidden layer activation function tanh was employed and subjected to training and testing. Linear correlation coefficients R equal to respectively and (figs 5a and 5b) were obtained. After training and testing the ANN was subjected to experimental verification and very good agreement between the results was found (fig. 5c). Hence it was concluded that the reliable neural identification of pull-adhesion f c,b of the top concrete layer from the base layer is possible on the basis of the parameters estimated by the three non-destructive s. f c,b, MPa 1,4 1,3 R=0,9775 1,2 1,1 1,0 0,9 0,8 0,7 0,6 0,5 0,4 0,3 0,2 0,1 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1,0 1,1 1,2 1,3 a) b) f b, MPa c) 1,2 1,1 1,0 R=0,9481 f c,b, MPa 1,4 1,3 R=0,9725 1,2 1,1 1,0 0,9 0,8 0,7 0,6 0,5 0,4 0,3 0,2 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1,0 1,1 1,2 1,3 f b, MPa 0,9 f c,b, MPa 0,8 0,7 0,6 0,5 0,4 0,3 0,2 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1,0 1,1 1,2 1,3 f b, MPa Fig. 5: Correlation between pull-off adhesion f b experimentally determined by semi-nondestructive pull-off method and pull-off adhesion f c,b identified by ANN for training (a), testing (b) and experimental verification (c) [28]. CONCLUSION A classification of non-destructive s useful for diagnosing transport infrastructure concrete structures has been proposed. Attention was drawn to the advanced acoustic s since the latter are especially suitable for assessing interlayer delamination and adhesion between concrete layers, as illustrated by the two examples. An Presented examples of the combined use of the impulse-response and the impact-echo to non-destructively identify delamination in underground garage concrete floor topping and the use of the above two s together with the optical

9 and artificial neural networks to non-destructively estimate the adhesion between the concrete layers was provided. Proposed methodology of the multi- NDT testing can be applied for condition assessment of various concrete structures of the transportation network, like: bridges, tunnels, retaining walls, road pavements, underground structures, etc. Acknowledgments This research has been carried out as a part of the Project Innovative resources and effective methods of safety improvement and durability of buildings and transport infrastructure in the sustainable development funded by the EU from the European Fund of Regional Development based on the Operational Program of the Innovative Economy. REFERENCES 1. Hola, J. Schabowicz, K. State-of-the-art nondestructive methods for diagnostics testing of building structures anticipated development trends, Archives of Civil and Mechanical Engineering, 2010, 10 (3): pp Olofsson, J., Elfgren, L., Bell, B., Paulsson, B., Niederleithinger, E., Jensen, J., Feltrin, G., Taljsten, B., Cremona, Ch., Kiviluoma, R., Bien, J. Assessment of European Railway Bridges for Future Traffic Demands and Longer Lives EC Project Sustainable Bridges, Structure and Infrastructure Engineering, 2005, 1 (2), pp Zwolski, J.; Bien, J. Modal Analysis of Bridge Structures by Means of Forced Vibration Tests, Journal of Civil Engineering and Management, 2011, 17 (4), pp Gorzelanczyk, T., Hola, J., Sadowski, L., Schabowicz, K. Methodology of Nondestructive Identification of Defective Concrete Zones in Unilaterally Accessible Massive Members, Journal of Civil Engineering and Management, 2013 (in the press). 5. Davis, A. The non-destructive impulse-response test in North America: , NDT&E International, 2003, 36 (4), pp Oh, S., Suh, B., Noh, M., Han, S., Kim, K., Cho, E. Non-destructive test for the assessment of concrete structure safety applied to full-scale test model, American Geophysical Union, Fall Meeting, 2009, American Concrete Institute Report ACI 228.2R-98, Nondestructive Test Methods for Evaluation of Concrete in Structures, ACI, Farmington Hills, Michigan, ASTM C Standard Practice for Evaluating the Condition of Concrete Plates Using the Impulse-Response Method. 9. Ottosen, N., Ristinmmaa, M., Davis, A. Theoretical interpretation of impulse-response tests of embedded concrete structures, Journal of Engineering Mechanics, 2004, 130 (9), pp Standard Test Method for Measuring the P-Wave Speed and the Thickness of Concrete Plates Using the Impact-echo Method, American Society For Testing And Materials, Sansalone, M., Streett, W. Impact-echo: Nondestructive Evaluation of Concrete and Masonry, Bullbrier Press, Ithaca, Schabowicz, K. Methodology for non-destructive identification of thickness of unilaterally accessible concrete elements by means of state-of-the-art acoustic s", Journal of Civil Engineering and Management, 2013, 19 (3), pp

10 13. Hola, J., Sadowski, L., Schabowicz, K. Nondestructive identification of delaminations in concrete floor toppings with acoustic methods, Automation in Construction, 2011, 20 (7), pp Bishko, A. Improvement of imaging at small depths for acoustic tomography of reinforced concrete objects, The 6th International Conference Non-Destructive Testing and Technical Diagnostics in Industry, Mashinostroenie, Moscow, Russia, Kozlov, V., Samokrutov, A., Shevaldykin, V. Thickness Measurements and Flaw Detection in Concrete Using Ultrasonic Echo Method, Journal of Nondestructive Testing and Evaluation, 1997, 13 (2): Hoegh, K., Khazanovich, L., Thomas H. Ultrasonic Tomography for Evaluation of Concrete Pavements", Transportation Research Record: Journal of the Transportation Research Board, 2011, 2232 (1), pp Schabowicz, K., Hola, J. Nondestructive elastic-wave tests of foundation slab in office building, Materials Transactions, 2012, 53 (2), pp Samokrutov, A., Kozlov, V., Shevaldykin, V., Meleshko, I. Ultrasonic defectoscopy of concrete by means of pulse-echo, 8th European conference for Non-Destructive Testing, Barcelona, Shevaldykin, V., Samokrutov, A., Kozlov, V. Ultrasonic Low-Frequency Short-Pulse Transducers with Dry Point Contact. Development and Application, International Symposium Non-Destructive Testing in Civil Engineering (NDT-CE), Proceedings on BB 85-CD, V66, Berlin, Gorzelanczyk, T., Hola, J., Schabowicz K. Nondestructive tests aimed at determining the thickness of the concrete shell of a heat pipe carrying tunnel, 18th World Conference on Nondestructive Testing, Durban, South Africa, Samokrutov, A., Kozlov, V., Shevaldykin, V. Ultrasonic testing of concrete objects using dry acoustic contact. Methods, instruments and possibilities, The 5th International Conference Non-Destructive Testing and Technical Diagnostics in Industry, Moscow, Russia, Samokrutov, A., Shevaldykin, V. Ultrasonic tomography of metal structures using the digitally focused antenna array method, Russian Journal of Nondestructive Testing, 2011, 47 (1), pp Hoegh, K., Khazanovich, L., Maser, K., Tran, N. Evaluation of Ultrasonic Technique for Detecting Delamination in Asphalt Pavements, Transportation Research Record: Journal of the Transportation Research Board, 2012, 2306 (1), pp Bishko, A., Samokrutov, A., Shevaldykin, A. Ultrasonic echo-pulse tomography of concrete using shear waves low-frequency phased antenna arrays, 17th World Conference on Nondestructive Testing, Shanghai, China, Hola, J., Sadowski, L. Testing interlayer pull-off adhesion in concrete floors by means of nondestructive acoustic methods, 18th World Conference on Non Destructive Testing, Durban, Sadowski, L. Nondestructive evaluation of bond between concrete layers in floors by means of artificial neural networks, PhD thesis, Wroclaw University of Technology, Wroclaw, Sadowski, L. Non-Destructive Evaluation Of The Pull-Off Adhesion Of Concrete Floor Layers Using RBF Neural Network", Journal of Civil Engineering and Management, (4), pp Sadowski, L., Hola, J. Neural prediction of the pull-off adhesion of the concrete layers in floors on the basis of nondestructive tests, Procedia Engineering, 57, 2013, pp