• 비파괴검사학회지
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• 제20권4호
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• pp.296-304
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• 2000

콘크리트 구조물의 성능평가 방법의 하나로 최근 들어 레이더가 널리 쓰이고 있다. 콘크리트 구조물 적용에 대한 레이더법의 발전을 위해서는, 콘크리트의 전자기적 재료 특성과 레이더의 작동원리를 이해하고, 활용하는 체계적인 연구노력이 필요하다. 본 논문에서는 레이더법의 유효 측정범위 설정과 레이더를 이용한 콘크리트의 두께측정 방법을 제시하고, 레이더 측정을 통한 콘크리트의 유전상수 계산 방법을 제안한다. 실험에서는 900mm (길이) $\times$ 600mm (폭)에 두께 50mm, 100mm, 150mm, 200mm, 250mm의 콘크리트 시편 5개를 사용하였다.

• Computers and Concrete
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• 제4권4호
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• pp.285-298
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• 2007

Corrosion of Reinforcement (rebar) is nondestructively estimated by the half-cell potential measurement. As is the case with other nondestructive testings (NDT), understanding of the underlying principles should be clarified in order to obtain meaningful results. Therefore, the measurement of potentials in concrete is analytically investigated. The effect of internal defects on the potentials measured is clarified numerically by the boundary element method (BEM). Thus, a simplified inversion by BEM is applied to convert the potentials on concrete surface to those on rebars, taking into account the concrete resistivity. Because the potentials measured on concrete surface are so sensitive to moisture content, concrete resistivity and surface condition, an inverse procedure to convert the potentials on concrete surface into those on rebars is developed on the basis of BEM. It is found that ASTM criterion is practically applicable to estimate corrosion from the potential values converted. In experiments, an applicability of the procedure is examined by accelerated corrosion tests of reinforced concrete (RC) slabs. For practical use, the procedure is developed where results of IBEM are visualized by VRML (Virtual Reality modeling Language) in three-dimensional space.

• Computers and Concrete
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• 제15권3호
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• pp.473-484
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• 2015

In this study, the availability of Schmidt hammer has been investigated as a reliable method to determine the quality of concrete in irrigation networks. For this purpose, the 28-day compressive strength of concrete material used in the construction irrigation channel of Bafra lowland, which is one of the most fertile plains in Turkey was examined by means of concrete compression and as well as concrete Schmidt hammer in laboratory conditions. This study was carried out on cylindrical samples to represent the everyday concrete party ($150m^3$) produced by contractor firm as 3 replications. The statistical analysis of experimental data showed that the correlations between the values of 28-day compressive strength of Schmidt hammer and the rebound number was found to be 0.98. Differences of the compressive strength between compression testing and Schmidt hammer were statistically significant at P<0.01. In this context, it was found that the reliability of compressive strength of the concrete compression test are excellent, also the reliability of compressive strength of Schmidt hammer are fair in assessing the quality of concrete irrigation channels.

• 한국구조물진단유지관리공학회 논문집
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• 제21권5호
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• pp.49-55
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• 2017

1970년대에 여러 연구자가 시제품 시험장비를 가지고 인발시험을 실시하였으며, 인발시험은 콘크리트 강도를 결정하는 신뢰할 만한 비파괴검사 방법(NDT)으로 입증되었다. 우리는 고강도 콘크리트 강도를 추정하기 위하여 직경 10 mm볼트에 홈이 파인 파단형 인발 볼트와 인발너트, 그리고 로드셀이 필요 없는 오일 유압펌프를 포함한 간이 인발시험법을 제안하였다. 저비용, 간편성 및 편의성을 갖는 간이인발시험의 이점을 검증하기 위하여, 30 MPa 및 50 MPa 급 두가지 유형의 콘크리트로 제작된 4개의 모의벽체를 대상으로 로드셀을 장착한 간이인발시험을 사용하여 인발시험을 실시하였다. 인발하중과 콘크리트 압축강도는 재령 7일까지는 매일, 그리고 14일, 21일, 28일에 측정되었다. 시험결과 인발하중과 콘크리트 압축강도는 매우 밀접한 상관관계를 보여주었으며 따라서 인발하중이 현장에서 구조물의 고강도 콘크리트 강도를 평가할 수 있다는 것을 확인할 수 있었다. 파단형 인발볼트 직경과 콘크리트 강도와의 관계식으로 y=0.05x+3.79(x=콘크리트 압축강도, y=파단형 인발볼트 직경)이 도출되었으며 결정계수는 0.88로 나타났다.

• 한국구조물진단유지관리공학회 논문집
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• 제6권4호
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• pp.91-98
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• 2002

Prediction for the compressive strength of concrete by non-destructive tests(NDT) has a tendency to show different outcomes according to various aggregates. The purpose of this study is to develop estimation equation by rebound number, ultrasonic velocity and combined method at concrete structures which used granite as coarse aggregates. The test variable is water/cement ratio(41.1%, 48.6%, 67.6%), curing method(moisture condition, dry condition) and age(7, 14, 28, 56). According to the test variable, new equation was suggested, and compared with the existing equations.

• Structural Monitoring and Maintenance
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• 제9권4호
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• pp.373-388
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• 2022

A USW based diagnostic procedure is presented for estimating the depth of surface-breaking cracks. The diagnosis is demonstrated on seven lab-scale SFRC beam specimens, which are subjected to the CMOD controlled three-point bending test to create real bending cracks. Then, the recorded multiple ultrasonic signals are examined with the signal processing techniques, including wavelet transform and two-dimensional Fourier transform, to investigate the relationships between the crack depth and two diagnostic indices, namely the attenuation coefficient and dispersion index (DI). Finally, the reliabilities of these indices for depth estimation are verified with the visually measured crack depths as well as the crack features obtained with a digital image processing algorithm. It is found that the DI outperforms the attenuation coefficient in depth estimation, where this index displays good agreement with the visual inspection for 86% of the inspected specimens.

• Computers and Concrete
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• 제19권5호
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• pp.467-475
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• 2017

The purpose of this study is to establish a prediction model for the electrical resistivity ($E_r$) of self-consolidating concrete by using waste LCD (liquid crystal display) glass as part of the fine aggregate and then, to analyze the results obtained from a series of laboratory tests. A hyperbolic function is used to perform nonlinear multivariate regression analysis of the electrical resistivity prediction model, with parameters such as water-binder ratio (w/b), curing age (t) and waste glass content (G). Furthermore, the relationship of compressive strength and electrical resistivity of waste LCD glass concrete is also found by a logarithm function, while compressive strength is evaluated by the electrical resistivity of non-destructive testing (NDT). According to relative regression analysis, the electrical resistivity and compressive strength prediction models are developed, and the results show that a good agreement is obtained using the proposed prediction models. From the comparison between the predicted analysis values and test results, the MAPE value of electrical resistivity is 17.0-18.2% and less than 20%, the MAPE value of compressive strength evaluated by $E_r$ is 5.9-10.6% and nearly less than 10%. Therefore, the prediction models established in this study have good predictive ability for electrical resistivity and compressive strength of waste LCD glass concrete. However, further study is needed in regard to applying the proposed prediction models to other ranges of mixture parameters.

• Advances in concrete construction
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• 제8권1호
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• pp.9-19
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• 2019

This paper describes an experimental investigation on hybrid fiber reinforced concrete (HYFRC) beams. And the main aim of this present paper is to examine the dynamic characteristics and damage evaluation of undamaged and damaged HYFRC beams under free-free constraints. In this experimental work, totally four RC beams were cast and analyzed in order to evaluate the dynamic behavior as well as static load behavior of HYFRCs. Hybrid fiber reinforced concrete beams have been cast by incorporating two different fibers such as steel and polypropylene (PP). Damage of HYFRC beams was obtained by cracking of concrete for one of the beams in each set under four-point bending tests with different percentage variation of damage levels as 50%, 70% and 90% of maximum ultimate load. And the main dynamic characteristics such as damping, fundamental natural frequencies, mode shapes and frequency response function at each and every damage level has been assessed by means of non-destructive technique (NDT) with hammer excitation. The fundamental natural frequency and damping values obtained through dynamic tests for HYFRC beams were compared with control (reference) RC beam at each level of damage which has been acquired through static tests. The static experimental test results emphasize that the HYFRC beam has attained higher ultimate load as compared with control reinforced concrete beam.

• 한국지반환경공학회 논문집
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• 제2권4호
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• pp.5-14
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• 2001

최근 구조물기초에 큰 변형 및 손상을 가하지 않고 안정성에 대한 정보를 비교적 쉽게 얻을 수 있는 비파괴시험(NDT, Non-Destructive Testing)기법이 큰 관심을 얻고 있다. 본 연구에서는 비파괴시험 중 검측공 기법(CSL, CT, PS)과 표면파 기법(SE, IR)을 현장타설말뚝의 건전도 평가에 이용하기 위한 적용성의 문제를 현장시험을 통하여 고찰하였다. 이를 위하여 결함이 없는 한 본의 정상말뚝과 연약선단, 단면축소 확대, 불량콘크리트 타설 등 현장에서 발생하기 쉬운 결함의 종류, 크기, 위치 등을 변화 조합한 9본의 현장타설말뚝(직경 0.4m, 길이 7.0m)을 시공하여 다양한 비파괴시험을 수행하였다. 시험을 통하여 각 기법을 현장타설말뚝의 건전도 평가에 적용할 때의 문제점과 각 기법의 합리적인 조합에 대하여 고찰하였다.

• KIEAE Journal
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• 제7권4호
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• pp.141-146
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• 2007

It is necessary to guarantee the safety, serviceability and durability of reinforced concrete structures over their service life. However, concrete structures represent a decrease in their durability due to the effects of external environments according to the passage of time, and such degradation in durability can cause structural degradation in materials. In concrete structures, some degradations in durability increase the corrosion of embedded rebars and also decrease the structural performance of materials. Thus, the structural condition assessment of RC materials damaged by corrosion of rebars becomes an important factor that judges needs to apply restoration. In order to detect the damage of reinforced concrete structures, a visual inspection, a nondestructive evaluation method(NDE) and a specific loading test have been employed. However, obscurities for visual inspection and inaccessible members raise difficulty in evaluating structure condition. For these reasons, detection of location and quantification of the damage in structures via structural response have been one of the very important topics in system identification research. The main objective of this project is to develope a methodologies for the damage identification via static responses of the members damaged by durability. Six reinforced concrete beams with variables of corrosion position and corrosion width were fabricated and the damage detections of corroded RC beams were performed by the optimization and the conjugate beam methods using static deflection. In results it is proved that the conjugate beam method could predict the damage of RC members practically.