• Journal of the Korean Society for Nondestructive Testing
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• v.36 no.2
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• pp.121-129
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• 2016

As the lifespan of concrete structures increases, their load carrying capacity decreases owing to cyclic loads and long-term effects such as creep and shrinkage. For these reasons, there is a necessity for stress state monitoring of concrete members. Particularly, it is necessary to evaluate the concrete structures for behavioral changes by using a technique that can overcome the measuring limitations of usual ultrasonic nondestructive evaluation methods. This paper proposes the use of a nonlinear ultrasonic method, namely, nonlinear resonant ultrasonic spectroscopy (NRUS) for the measurement of nonlinearity parameters for stress monitoring. An experiment compared the use of NRUS method and a linear ultrasonic method, namely, ultrasonic pulse velocity (UPV) to study the effects of continuously increasing loads and cyclic loads on the nonlinearity parameter. Both NRUS and UPV methods found a similar direct relationship between load level and that parameter. The NRUS method showed a higher sensitivity to micro-structural changes of concrete than UPV method. Thus, the experiment confirms the possibility of using the nonlinear ultrasonic method for stress state monitoring of concrete members.

• Journal of the Korean Society for Nondestructive Testing
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• v.19 no.4
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• pp.259-269
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• 1999

Elastic wave velocity measurement technique such as impact-echo method and ultrasonic pulse velocity method has been successfully used to evaluate the moduli and strength of concrete. However, estimation results obtained by the NDT methods do not agree well with real things because longitudinal wave velocity is influenced by various factors. In this paper, among several factors influencing P-wave velocity, the influence of moisture content in concrete was investigated through the experiment. Test results show that longitudinal wave velocity is significantly affected by the moisture content of concrete, i.e., the lower moisture content. the lower velocity. Moisture content influences rod-wave velocity measured by impact-echo method stronger than ultrasonic pulse velocity measured by transmission method. During drying process with ages. the difference of increasing rate between longitudinal wave velocity and compressive strength of concrete is gradually increased. Therefore, to establish more accurate relationship between longitudinal wave velocity and strength, the difference of the increasing rate should be considered.

• Proceedings of the Korea Concrete Institute Conference
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• 1999.04a
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• pp.697-702
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• 1999

Among several non-destructive testing methods, ultrasonic pulse velocity method has been widely used for the evaluation of concrete strength. However, this method might not provide accurate estimated results since factors influencing the relationship between strength and wave velocity is not considered. In this study, the evaluation methods of concrete strength using compression wave velocities measured by either ultrasonic pulse velocity method or impact-resonance method are proposed. A basic equation is obtained by the linear regression with velocity vs. strength data at a specific age and then, ageing factor is employed in the equation to consider the difference of the increasing rate between wave velocity and strength. Strengths predicted by the proposed equation agree well with test results.

• Proceedings of the Korea Concrete Institute Conference
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• 2001.05a
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• pp.795-800
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• 2001

Two evaluation techniques of the tunnel lining concrete using ultra sonic velocity method are developed. Modified linear regression technique is proposed to enhance the corelation between the pulse velocity and the compressive strength of core specimens. And bivariate normal distribution is assumed to evaluate the quality of concrete as a terms of compressive strength. A simple corelation table between the pulse velocity and the compressive strength of core specimens are proposed.

• Journal of the Korean Institute of Navigation
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• v.20 no.3
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• pp.85-95
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• 1996

In the velocimeter, the ultrasonic pulse signal is used for measuring the profile velocity of moving targets distributed in space because of the merits of its high distance resolution and harmless affect to the human body. The velocity reading in conventional ultrasonic pulsed velocimeter depends on the wave pattern reflecting the spatial distribution of scatters and includes observational error due to the signal processing of analyzing pulse signal. In this paper, we evaluate an influence of the received waveform of pulsed signal on the velocity information by setting a model. Subsequently, in order to improve the distance resolution and to obtain precise velocity information without the influence of the spatial distribution of scatterers, we propose a new method for the analysis of Doppler pulsed signal, in which the pulsed signal is transformed into a phase function with local data. Finally, it is confirmed that the performance of the velocimeter is more improved in the proposed method than in the conventional one.

• Journal of the Korean Recycled Construction Resources Institute
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• v.2 no.3
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• pp.209-216
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• 2014

One of the widely used NDT(Non-destructive techniques) is the ultrasonic pulse velocity (USPV) method, which determines the travel time of the ultrasonic pulse through the tested materials and most studies were focused on the results expressed in time domain. However, the signal of ultrasonic pulse in time domain can be transformed into frequency domain, through Fast fourier transform(FFT) to give more useful informations. This paper shows a comparison of changes in the pulse velocity and frequency domain signals of concrete for various load histories using lightweight fine aggregates. The strength prediction equation for normal concrete using USPV cannot be used to estimate lightweight fine aggregate concrete strength. The signals in frequency domain of ultrasonic pulse of lightweight fine aggregate concrete does not show any significant difference comparing with those of normal concrete. The increases in stress levels of concrete change the pulse velocities and maximum frequencies, however the apparent relationship between themselves can not be found in this experiment.

• Computers and Concrete
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• v.3 no.6
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• pp.423-437
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• 2006

Stress wave propagation through concrete is simulated by finite element analysis. The concrete medium is modeled as a homogeneous material with smeared properties to investigate and establish the suitable finite element analysis method (explicit versus implicit) and analysis parameters (element size, and solution time increment) also suitable for rigorous investigation. In the next step, finite element analysis model of the medium is developed using a digital image processing technique, which distinguishes the mortar and aggregate phases of concrete. The mortar and aggregate phase topologies are, then, directly mapped to the finite element mesh to form a heterogeneous concrete model. The heterogeneous concrete model is then used to simulate wave propagation. The veracity of the model is demonstrated by evaluating the intrinsic parameters of nondestructive ultrasonic pulse velocity testing of concrete. Quantitative relationships between aggregate size and testing frequency for nondestructive testing are presented.

• Journal of the Korean Society for Nondestructive Testing
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• v.14 no.2
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• pp.90-100
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• 1994

Ultrasonic velocities are widely used in the investigation of material properties. In this paper, a micromechanics model and the ultrasonic velocity were used to develop a nondestructive method to determine the density variation due to porosity in structural SiC. The micromechanics model developed can consider the pore shape and orientation. The model also takes into account the interaction between pores so that it can be applied to the material with high porosity content. A contact pulse overlap method was used to measure the ultrasonic velocities of porous SiC samples, and there was a linear correlation between the velocity and density (or porosity). Using the model and the measured velocity, the bulk density can be easily calculated. The calculated density was in good agreement with that obtained by Archimedes' method.

• Journal of the Korea Institute of Building Construction
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• v.23 no.6
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• pp.683-692
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• 2023

This research assesses the mechanical properties of concrete, utilizing both normal and lightweight aggregates, through measurements of compressive strength and ultrasonic pulse velocity. The study observed that concrete with normal aggregates exhibited higher compressive strength in its initial stages, whereas concrete with lightweight aggregates showed increased strength over time, likely attributed to the higher water absorption rate of lightweight aggregates. Ultrasonic pulse velocity generally registered higher in normal aggregate concrete, barring a specific duration, presumably due to variations in the internal pore structure of the aggregates. The correlation coefficient(R²) for the strength prediction equation, derived from the relationship between compressive strength and ultrasonic pulse velocity, exceeds 0.95. This high correlation suggests that the predictive equation based on these experimental findings is a reliable method for estimating concrete strength.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.165-168
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• 2008

This study performed the 3-dimensional inspection analysis for cavitation by using the ultrasonic pulse velocity method to detect detailed various cavitations in a concrete test material. The internal-void are made of non-void test material and two types of which a regular square type and a rectangle type that produced through the 3-dimensional cavitation to put into a $500{\ast}500{\ast}500mm$ sized non-reinforced concrete test material. The tomography method for the ultrasonic pulse velocity method was used for the non-destructive test. As a result, this study has found that it is possible to visualize the cavitation as an image, and to analyze the internal-void in detail by the non-destructive method.