• 콘크리트학회논문집
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• 제16권3호
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• pp.375-382
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• 2004

콘크리트의 압축강도는 콘크리트 구조물의 설계 시에 재료상수로 사용되는데 이 값의 산정에 사용되는 공시체의 크기 및 형상이 각 나라마다 다르므로 현재까지도 문제가 되고 있다. 본 연구에서는 콘크리트 공시체의 압축강도에 공시체의 크기와 형상이 미치는 영향을 파괴역학적 이론과 실험을 통하여 검토하였다. 콘크리트의 두 가지 파괴모드 중의 하나인 모드 I에 대한 실험이 원주공시체, 입방체, 그리고 각주를 이용하여 수행되었다 먼저 원주공시체, 입방체와 각주 자체의 크기효과와 이들 사이의 형상효과를 살펴본 후, 공시체의 크기, 형상, 및 타설방향에 대한 압축강도의 상호관계에 대하여 검토하였다. 또한, 입방체와 각주에 대하여 타설방향이 압축강도에 미치는 영향을 검토하였다.

• 한국농공학회:학술대회논문집
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• 한국농공학회 1998년도 학술발표회 발표논문집
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• pp.146-149
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• 1998

In this study, the chloride ion penetration test and the compressive strength test should be done simultaneously on the standard cylinder specimen. And from analyzing the data from those tests, a strength estimation equation with high credibility is to be developed.

• International Journal of Concrete Structures and Materials
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• 제5권1호
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• pp.49-55
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• 2011

The main objective of this investigation is to study size effect on compressive strength of CFRP confined concrete cylinders subjected to axial compressive loading. In total 24 concrete cylinders with different sizes were tested, small specimens with a diameter of 100 mm and a height of 200 mm, medium specimens with a diameter of 200 mm and a height of 400 mm, and big specimens with a diameter of 300 mm and a height of 600 mm. The lateral confining pressure of each specimen is the same and from that hypothesis the small specimens were confined with one layer of CFRP, medium and big specimens were performed by two and three layers of CFRP respectively. Test results indicate a significant enhancement in compressive strength for all confined specimens, and moreover, the compressive strengths of small and medium specimens are almost the same while a bit lower for big specimens. These results permit to conclude that there is no size effect on compressive strength of confined specimens regardless of cylinder dimension.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2003년도 가을 학술발표회 논문집
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• pp.351-354
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• 2003

Triaxial behavior of concrete cylinders wrapped with FRP material has been investigated for the increase of concrete strength by lateral confinement. Using the model by Richart et al., a modified empirical equation was proposed to estimate the strength of concrete cylinders with FRP confinement based on the linear relationship between the concrete strength and lateral confining pressure. From the experimental stress-strain result of the cylinder specimens having similar confining pressure, less ductility was observed for higher strength concrete. But the compressive strength of the specimen was linearly increased by lateral confinement. The confinement effectiveness coefficient for the strength enhancement of the cylinders by FRP wrap was obtained as 2.27 from the regression analysis.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2006년도 춘계 학술발표회 논문집(II)
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• pp.125-128
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• 2006

As the ministry of construction and transportation established quality standards for recycled aggregate in August, 2005, the consumption of recycled aggregates is expected to be increased in construction fields in the future. Thus the relations between compressive strength of general concretes and that of recycled aggregate concretes which are applied to actual structures are attempted to investigate through non-destruction testing method. Presently Schmitt-Hammer test method is that concrete compressive strength is predicted by measuring surface hardness of concretes, and is well known as the most convenient and simply operated method among many non-destruction testing methods. In this study, cylinder specimen and mock-up were constructed using recycled aggregate concretes made by the first class recycled coarse aggregates and recycled fine aggregates specified in KS F 2573 (recycled aggregate for concrete), and compressive strength of hardened concrete of middle ages was evaluated.

• KCI Concrete Journal
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• 제12권2호
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• pp.85-93
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• 2000

Potentially significant mechanical improvements in tension can be achieved by the incorporation of randomly distributed, short discrete fibers in concrete. The improvements due to the incorporation fibers significantly influence the composite stress - strain ($\sigma$-$\varepsilon$) characteristics. In general incorporating fibers in a plain concrete has relatively small effect on its precracking behavior. It, however, alters its post-cracking behavior quite significantly, resulting in greatly improved ductility, crack controls, and energy absorption capacity (or toughness). Therefore, a thorough understanding the complete tensile stress - strain ($\sigma$-$\varepsilon$) response of fiber reinforced concrete is necessary for proper analysis while using structural components made with fiber reinforced concrete. Direct tensile stress applied to a specimen is in principle the simplest configuration for determining the tensile response of concrete. However, problems associated with testing brittle materials in tension include (i) the problem related to gripping of the specimen and (ii) the problem of ensuring centric loading. Routinely, indirect tension tests for plain concrete, flexural and split-cylinder tests, have been used as simpler alternatives to direct uniaxial tension test. They are assumed to suitable for fiber reinforced concrete since typically such composites comprise 98% by volume of plain concrete. Clearly since the post-cracking characteristics are significantly influenced by the reinforcing parameters and interface characteristics, it would be fundamentally incorrect to use indirect tensile tests for determining the tensile properties of fiber reinforced concrete. The present investigation represents a systematic look at the failure and toughening mechanisms and macroscopic stress - strain ($\sigma$-$\varepsilon$) characteristics of fiber reinforced concrete in the uniaxial tension test. Results from an experimental parametric study involving used fiber quantity, type, and mechanical properties in the uniaxial tension test are presented and discussed.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2012년도 춘계 학술논문 발표대회
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• pp.63-64
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• 2012

In case of concrete, it should be deformed by many factors, such as explosive spalling, thermal strain and creep at high temperature. Structural fire design has been proposed to predict fire damage as national standard. It is general safer to use values obtained from tests of unstressed residual test in stead of stressed test. But most of thermal properties on concrete were conducted with normal aggregate. In this study, it evaluated mechanical properties of concrete with aggregate type and loading condition. we use normal and light aggregate to have different thermal properties. Also, we test mechanical properties to use Ø100×200 mm cylinder specimen according to target temperature and 0%, 20%, 40% loading.

• 한국산학기술학회논문지
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• 제17권9호
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• pp.552-558
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• 2016

최근 노후화된 콘크리트 건축물에 대한 보수 및 보강에 대한 관심이 높아지고 있는데 이러한 건축물에 대한 안전성을 정확히 평가하기 위해서는 콘크리트 강도를 필수적으로 알아야 한다. 이러한 콘크리트 강도를 평가하는 방법으로 코어채취 방법이 가장 효과적이며 많이 사용되는 방법이다. 그런데 구조물에 따라 경우에 따라서는 어쩔 수 없이 철근이 포함된 코어가 채취되는데 코어 강도를 평가하기 위한 규정에는 이러한 철근이 포함된 코어 사용을 인정하지 않고 있다. 따라서 본 연구는 콘크리트 구조물의 건전성을 평가하고자 하는 안전진단 및 보수 보강 관련 업체에 철근이 포함된 코어 공시체에 대한 콘크리트 강도를 정확하게 평가할 수 있도록 우리나라 실정에 맞는 정량적인 강도 판정기준을 제시하고자 하였다. 이러한 연구를 수행하기 위하여 1종류의 무 배근과 14종류의 배근을 한 공시체를 준비 하였고 압축강도 시험을 실시하였다. 결과적으로 철근체적으로 약 $50cm^3$까지 배근된 경우(직경 13mm인 철근 4개 정도)의 공시체의 강도는 무배근 공시체 강도의 80% 정도 이상이라는 것을 예측할 수 있다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2001년도 가을 학술발표회 논문집
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• pp.669-674
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• 2001

Electric Arc Furnace Dust (EAF Dust) Is residual dust produced during the manufacturing of metal products from heavily heated electric arc furnace. Many researches have focused on recycling and reusing EAF Dust for industrial and construction purposes. However, most of these researches were aimed at obtaining useful heavy metal powders by treating toxic metallic materials in EAF Dust. Also, few researches dealt with using EAF Dust as admixture in concrete mixture (i.e., slag dust). In this study, EAF Dust is used as admixture in concrete mixture content considering economical feasibility and construction applicability. The concrete specimens mixed with EAF Dust is then tested in compression and tension to study its strength and ductility as well as its failure mechanism. The compression and tension (by split cylinder test) test results are compared to the results from the specimens without EAF Dust to understand the chemical stability and mechanical characteristic of concrete specimens with EAF Dust. For the experiment, 6 types of admixture added concrete were studied: ⑴Combination of EAF Dust and blast-furnace slag in 1 to 1 ratio, ⑵Combination of EAF Dust and blast-furnace slag in 1 to 2 ratio, ⑶EAF Dust only, ⑷blast-furnace slag only, ⑸fly ash only, and ⑹no admixture. The experimental results show that the strength of EAF Dust added specimen has lower early age strength but higher 28 day strength when compared to other specimens. Also, the Elastic Modulus of EAF Dust is higher(28 days) than other specimens. The study results prove that EAF Dust can be used as an effective admixture in concrete for specific usages.

• 한국건축시공학회지
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• 제8권3호
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• pp.85-91
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• 2008

Out of all the nondestructive test (NDT) methods, the pullout test is one of the most reliable techniques for estimating the strength of concrete under construction. However the pullout test inevitably produces significant surface damage because of the inherent test mechanism and costs too much for using measurement devices. In the view of construction engineers and inspectors, the main purpose of NDT methods for concrete is to verify whether the concrete strength of structure members exceeds the target strength or not. In this paper, a new pullout test method, which involves a pre-installed breaking bolt, with pre-determined breaking torques corresponding to the target strength of concrete, is introduced with related test data. The three types of test, the rebound hammer test, the pullout test, and the new pullout test with breaking bolt, were carried out on wall specimen with three types of concrete strengths. Our results show that concrete strength as evaluated by the pullout test with breaking bolt was similar with cylinder test results. Therefore it can be said that the new pullout test with breaking bolt is a useful method for checking the concrete strength without any surface damages in construction site.