• Computers and Concrete
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• 제15권4호
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• pp.503-514
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• 2015

Fibre-added concretes are frequently used in large site applications such as slab and airports as well as in bearing system elements or prefabricated elements. It is very difficult to determine the mechanical properties of the fibre-added concretes by experimental methods in situ. The purpose of this study is to develop an artificial neural network (ANN) model in order to predict the compressive and bending strengths of hybrid fibre-added and non-added concretes. The strengths have been predicted by means of the data that has been obtained from destructive (DT) and non-destructive tests (NDT) on the samples. NDTs are ultrasonic pulse velocity (UPV) and Rebound Hammer Tests (RH). 105 pieces of cylinder samples with a dimension of $150{\times}300mm$, 105 pieces of bending samples with a dimension of $100{\times}100{\times}400mm$ have been manufactured. The first set has been manufactured without fibre addition, the second set with the addition of %0.5 polypropylene and %0.5 steel fibre in terms of volume, and the third set with the addition of %0.5 polypropylene, %1 steel fibre. The water/cement (w/c) ratio of samples parametrically varies between 0.3-0.9. The experimentally measured compressive and bending strengths have been compared with predicted results by use of ANN method.

• Computers and Concrete
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• 제10권4호
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• pp.409-417
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• 2012

The quality of high performance concrete largely depends on water cement ratio, porosity, material composition and mix methods. The uniformity of color, texture and compressive strengths are quality indicators commonly used to assess the overall characteristics of concrete mixes. The homogeneity and share of coarse aggregates play a key role in concrete quality and must be analyzed in a microscopic point of view. This research studies the quality of high performance concrete by taking drilled cores in both horizontal and vertical directions from a 1.0 $m^3$ specimen. The coarse aggregate, expressed in digitized $100{\times}116$ dpi resolution images are processed based on brightness in colors through commercial software converted into text files. With the image converting to text format, the share of coarse aggregate is quantified leading to a satisfactory assessment of homogeneity - a quality index of high performance concrete. The compressive strengths of concrete and the shares of coarse aggregate of the samples are also compared in this research study to illustrate its correlation in concrete quality. It is concluded that a higher homogeneity of aggregate exists in the vertical plane than that of the horizontal planes of the high performance concrete. In addition, the concrete specimen showing denser particle packing has relatively higher compressive strengths. The research methodology provides an easy-to-use, direct measurement of high performance concrete when conducting quality assessment in the construction site.

• 콘크리트학회지
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• 제7권2호
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• pp.136-145
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• 1995

본 연구는 천연 굵은 골재 50%를 재생골재로 대치시켜 제조한 재생콘크리트를 일반 구조물에 사용할 수 있도록 성능을 향상시키기 위한 연구의 일환으로 수행되었다. 쇄석골재 사용시의 배합설계 방법으로 콘크리트를 제조하였고 일반적인 수중양생으로 공시체를 야생하였다. 재생콘크리트의 성능향상을 목적으로 유동화제와 플라이애쉬를 첨가하였다. 압축강도 등 각종 강도와 파괴인성 등을 측정하여 이를 일반콘크리트와 비교한 결과 재생콘크리트는 강도와 탄성계수가 낮고 변형율이 크며 파괴인성도 낮았다. 그러나 유동화제의 사용으로 물-시멘트비를 35%까지 낮추므로써 슬럼프 $16{\pm}2$cm에서 일반 구조물에 소요 압축강도보다 높은$225kg/cm^2$이상의 압축강도를 얻었다. 하지만 재생콘크리트를 일반 구조물에 사용을 위해서는 탄성계수와 변형율에 대한 향상이 필요하다. 또한 플라이애쉬의 사용은 장기 강도 증진 효과를 보이는 반면 강도 저하를 유발했다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2001년도 가을 학술발표회 논문집
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• pp.217-220
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• 2001

Due to the tendency of increase in demolished-concrete produced by alteration and deterioration of concrete structures, recycling of those demolished-concrete is necessary to solve the exhaustion of natural aggregate, in order to save resources and protect environment, especially being want of resources in Korea. For this purpose, concrete made with the pozzolanic cement and recycled aggregate was tested for compressive and tensile strength. The pozzolanic cement was a mixture of OPC(Ordinary Portland Cement) and pozzolans such as fly ash, other siliceous materials and early rapid hardening cement(ERC). It was found that the compressive strength of the pozzolanic cement was enhanced when 0.75% of ERC was dozed, as compared with OPC mortar. It was also shown that compressive and tensile strength of concrete with recycled aggregate and pozzolanic cement were higher than those of concrete with crushed stones and OPC. It was concluded that the pozzolanic cement influenced on the increase of concrete strengths with recycled aggregate.

• Structural Engineering and Mechanics
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• 제17권2호
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• pp.141-152
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• 2004

The bonding behaviors of Lightweight Aggregate Concrete (LWAC) and normal weight concrete were investigated experimentally. Pull-out tests were carried out to measure the bond strengths of three groups of specimens with compressive strength levels of 60, 40, and 20 MPa, respectively. Test results showed that the difference in the bond failure pattern between LWAC and normal weight concrete was significant as the concrete compressive strength became lower than 40 MPa. The corresponding bond strengths of LWAC were lower than that for normal weight concrete. As the compressive strength of concrete became relatively high (> 40 MPa), a bond failure pattern in normal weight concrete occurred that was similar to that in LWAC. The bond strength of LWAC is higher than that for normal weight concrete because it possesses higher mortar strength. Stirrup use leads to an increase of approximately 20% in nominal bond strength for both types of concrete at any strength level.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2000년도 가을 학술발표회 논문집(II)
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• pp.1139-1144
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• 2000

Recent advance in material technology has accelerated the development of high strength concrete using lightweight artificial aggregates. The lightweight concrete has many advantages that the reduction of dead lads and the increase in load capacity can ofter. In this study, lightweight polymer concrete using unsaturated polyester resin and lightweight aggregate were prepared and tested for testing the physical and the mechanical properties. The compressive strengths of lightweight polymer concretes with specific gravities from 1.32 to 1.78 were compressive strength of 250 to 470 $kgf/cm^2$ and flexural strengths were measured to be in the range of a third to a quarter of compressive strength

• Advances in concrete construction
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• 제3권1호
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• pp.55-69
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• 2015

Tailing Material (TM) and Fly Ash (FA) are obtained as waste products from the mining and thermal industries. Studies were carried out to explore the possibility of utilizing TM as a part replacement to fine aggregate and FA as a part replacement to cement, in concrete mixes. The effect of replacing fine aggregate by TM and cement by FA on the standard sized specimen for compressive strength, split tensile strength, and flexural strengths are evaluated in this study. The concrete mix of M40 grade was adopted with water cement ratio equal to 0.40. Concrete mix with 35% TM and 65% natural sand (TM35/S65) has shown superior performance in strength as against (TM0/S100, TM30/S70, TM40/S60, TM50/S50, and TM60/S40). For this composition, studies were performed to propose the optimal replacement of Ordinary Portland Cement (OPC) by FA (Replacement levels studied were 20%, 30%, 40% and 50%). Replacement level of 20% OPC by FA, has shown about 0-5% more compressive strength as against the control mix, for both 28 day and 56 days of water curing. Interestingly results of split tensile and flexural strengths for 20% OPC replaced by FA, have shown strengths equal to that of no replacement (control mix).

• 콘크리트학회논문집
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• 제18권2호
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• pp.219-226
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• 2006

본 연구에서는 복합 재질 폐플라스틱을 재활용한 폴리머콘크리트의 압축, 휨 및 충격강도, 흡수율 및 동결융해저항성에 미치는 결합재 첨가량 및 PA 혼입량의 영향에 대하여 연구하였다. 그 결과 복합 재질 폐플라스틱을 재활용한 폴리머콘크리트의 압축, 휨 및 충격강도는 PA 혼입량에 관계없이, 결합재 첨가량 및 충전제 혼입량의 증가에 따라 증가하는 경향을 나타냈다. 하지만, PA 혼입량의 증가에 따라서는 감소하는 경향을 보였다. 복합 재질 폐플라스틱을 재활용한 폴리머콘크리트의 흡수율은 PA 혼입량에 관계없이, 결합재 첨가량의 증가에 따라 감소하는 경향을 나타냈다. 하지만 PA 혼입량의 증가에 따라서는 증가하는 경향을 나타냈다. 복합 재질 폐플라스틱을 재활용한 폴리머콘크리트의 내구성 지수는 결합재 첨가량의 증가에 따라 증가하였으나, PA 혼입량에 따라서는 감소하는 경향을 보였다.

• Computers and Concrete
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• 제9권2호
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• pp.153-169
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• 2012

The contribution of steel fibers on the 28-day compressive strength of high-performance steel fiber reinforced concrete was investigated, is presented. An extensive experimentation was carried out over water-cementitious materials (w/cm) ratios ranging from 0.25 to 0.40, with silica fume-cementitious materials ratios from 0.05 to 0.15, and fiber volume fractions ($V_f$= 0.0, 0.5, 1.0 and 1.5%) with the aspect ratios of 80 and 53. Based on the test results of 44 concrete mixes, mathematical model was developed using statistical methods to quantify the effect of fiber content on compressive strength of HPSFRC in terms of fiber reinforcing index. The expression, being developed with strength ratios and not with absolute values of strengths, is independent of specimen parameters and is applicable to wide range of w/cm ratios, and used in the mix design of steel fiber reinforced concrete. The estimated strengths are within ${\pm}3.2%$ of the actual values. The model was tested for the strength results of 14 mixes having fiber aspect ratio of 53. On examining the validity of the proposed model, there exists a good correlation between the predicted values and the experimental values of different researchers. Equation is also proposed for the size effect of the concrete specimens.

• 터널과지하공간
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• 제2권2호
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• pp.224-236
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• 1992

It is very important to determine the thermo-mechanical characteristics of the rock mass surrounding the repository of radioctive waste and the LPG storage cavern. In this study, Hwasoon-Shist. Dado-Tuff adn Chunan-Tonalite were the selected rock types. Temperature dependence of the mechanical properteis such as uniaxial compressive strength, tensile strength, Young's modulus was investigated by measuring the behaviour of these properties due to the variation of temperature. Also, the characteristics of strength and deformation of these rocks were examined through high-temperature triaxial compression tests with varing temperatures and confining pressures. Important results obtained are as follows: In high temperature tests, the uniaxial compressive strength and Yong's modulus of Tonalite showed a sligth increase at a temperature up to 300$^{\circ}C$ and a sharp decrease beyond 300$^{\circ}C$, and the tensile strength showed a linear decrease with increasing heating-temperature. In high-temperature triaxial compression test, both the failure stress and Young's modulus of Tonalite increased with the increase of confining pressure at constant heating-temperature, and the failure stress decreased at 100$^{\circ}C$ but increased at 200$^{\circ}C$ under a constant confining pressure. In low temperature tests, the uniaxial compressive and tensile strengths and Young's modulus of these rocks increased as the cooling-temperature is reduced. Also, the uniaxial compressive and tensile strengths of wet rock specimens are less than those of dry rock specimens.