Nächste SlideShare
Ultrasonic testing report-JUNE 2018Ultrasonic testing report-JUNE 2018
Wird geladen in ... 3
1 von 1

Más contenido relacionado


  1. 248 ACI Materials Journal/May-June 2010 ACI MATERIALS JOURNAL TECHNICAL PAPER ACI Materials Journal, V. 107, No. 3, May-June 2010. MS No. M-2009-091.R1 received April 8, 2009, and reviewed under Institute publication policies. Copyright © 2010, American Concrete Institute. All rights reserved, including the making of copies unless permission is obtained from the copyright proprietors. Pertinent discussion including authors’ closure, if any, will be published in the March-April 2011 ACI Materials Journal if the discussion is received by December 1, 2010. A novel technique based on wavelet time-frequency decomposition was applied in the analysis of ultrasonic pulses. With the method, frequency-dependent attenuation and velocity can be calculated for both longitudinal and shear waves. A total of 14 specimens with five different mixture proportions were scrutinized and the results demonstrated the viability of a high frequency ultrasound (above 100 kHz) to analyze cement-based materials. The technique applied the continuous wavelet transform and had advantages when compared to any Fourier-based method. A method to analyze grain-size distribution based on the properties of the Rayleigh, stochastic, and diffuse attenuation regions was also presented. The procedure relied on the wavelet calculation of frequency- dependent attenuation and yielded estimates of aggregate proportions. The capability of extracting frequency-dependent parameters via wavelet transform can be used for any nondestructive testing method based on wave propagation, such as impact-echo or acoustic emission. Keywords: attenuation; cement-based materials; frequency analysis; grain-size distribution; nondestructive testing; phase velocity; ultrasonic testing; wavelets. INTRODUCTION Nondestructive evaluation (NDE) methods have received a great deal of attention in the last decades. The application of NDE methods for the assessment of aging structures, as well as for quality control of new ones, has reached such a level of importance that it has been considered for biennial inspections of bridges in the U.S.1,2 The application of NDE methods is advantageous when compared with traditional destructive techniques; and two important characteristics of NDE testing— namely, the fact that in most cases NDE can be applied for in- place inspections and its nondestructive character—yield their applicationveryappealing,inparticularforstructuresthat are in use while they need to be assessed. Some of the NDE techniques that have been successfully applied for the investigation of concrete include impact-echo, acoustic emission, radar, sonic methods, surface hardness methods, acoustic tomography, and ultrasound; among these methods, the ultrasound technique is the only one that allies flexibility, low cost, and the capability of yielding information about the microscopic concrete structure. As a result, the ultrasound technique has been used to evaluate diffuse forms of damage in concrete3-7 to determine early-age properties of cement-based materials, to characterize porosity and inclusions in hardened cement paste,8 and to determine dynamic properties of concrete. An important aspect of ultrasonic investigation—one that is sometimes forgotten in the experiments described in the literature—is the existence of three interrelated parameters that are associated with wave propagation in a dispersive anisotropic medium. The ultrasonic testing of cement-based materials delivers velocity, amplitude, and attenuation measurements that are interrelated and can be used for obtaining information about diffuse damage, the onset and propagation of microcracks, and mixture characteristics. The capability to obtain frequency-dependent velocities and attenuation is an important issue in the analysis of the three ultrasonic parameters’ interaction. Some difficulties in obtaining frequency-dependent velocity and attenuation for frequencieswhosewavelengthhasthesameorderofmagnitudeof fine aggregate typically used in concrete are reported in the literature.9,10 Nonetheless, a full understanding of frequency-dependent attenuation processes that take place in ultrasonic wave propagationincement-basedmaterialsisan a priori condition to the reliable interpretation of ultrasonic data. Furthermore,asreportedintheliterature,thepeakfrequencyofthe ultrasonic signal is very sensitive to environmental damage.5 In fact, some specific forms of diffuse damage in concrete affect the attenuation of higher frequency pulses only.4,11 In addition to the aspects related to diffuse damage, it is important to emphasize that even basic ultrasonic measurements, such as pulse velocity, are strongly affected if the support medium is dispersive—that is, somecomponentsofthepulsearemoreattenuatedordelayedthan others—and grain size distribution and porosity also affect ultrasonic attenuation. The frequency-dependent attenuation of ultrasonic pulses has been one of the main concerns of concrete investigation. Through ultrasonic signal partitioning with a discrete windows-in-time domain, Gaydecki et al.12 concluded that it is possible to extract some information related to the size distributions of the aggregate. A method to determine frequency-dependentultrasonicpulseattenuationincement-based materials was developed by Landis and Shah.9 The authors manifest skepticism regarding high-frequency ultrasonic applications in cement-based materials and urge for the development of new tools in ultrasonic nondestructive testing. Owino and Jacobs,13 using laser ultrasound, investigated the frequency-dependent material attenuation of Rayleigh waves and concluded that, within some coherence intervals, the material attenuation coefficient was linear. The researchers also emphasized that it was possible to characterize the microstructure of cement-based materials from ultrasonic attenuation losses. The effect of aggregate size on the attenuation of Rayleigh surface wavesincementitiousmaterialswasalsoinvestigatedbythesame authors.14 One of the conclusions from the experiments was that absorption losses played a major role in the attenuation, and the scattering losses were negligible. The authors also concluded the existence of extreme difficulties in relating attenuations losses to the microstructure of cement-based materials. The ultrasound analysis of a portland cement-paste matrix with glass bead inclusions was performed by Becker et al.6 ; the experiments Title no. 107-M29 Wavelet Analysis of Ultrasonic Pulses in Cement-Based Materials by Carnot Leal Nogueira