• Advances in concrete construction
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• 제15권1호
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• pp.23-39
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• 2023

One of the important problems of concrete placing is the concrete compaction, which can affect the strength, durability and apparent quality of the hardened concrete. Therefore, vibrating operations might be accompanied by much noise and the need for training the involved workers, while inappropriate functioning can result in many problems. One of the most important methods to solve these problems is to utilize self-compacting cementitious composites instead of the normal concrete. Due to their benefits of these new materials, such as high tensile, compressive, and flexural strength, have drawn the researchers' attention to this type of cementitious composite more than ever. In this experimental investigation, six mixing designs were selected as a base to acquire the best mechanical properties. Moreover, forty-eight rectangular composite panels with dimensions of 300 mm × 400 mm and two thickness values of 30 mm and 50 mm were cast and tested to compare the flexural and impact energy absorption. Steel fibers with volume fractions of 0%, 0.5% and 1% and with lengths of 25 mm and 50 mm were imposed in order to prepare the required cement composites. In this research, the composite panels with two thicknesses of 30 mm and 50 mm, classified into 12 different groups, were cast and tested under three-point flexural bending and repeated drop weight impact test, respectively. Also, the examination and comparison of flexural energy absorption with impact energy absorption were one of the other aims of this research. The obtained results showed that the addition of fibers of longer length improved the mechanical properties of specimens. On the other hand, the findings of the flexural and impact test on the self-compacting composite panels indicated a stronger influence of the long-length fibers.

• Computers and Concrete
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• 제13권6호
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• pp.709-737
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• 2014

Fibre-reinforced self-compacting concrete (FRSCC) is a high-performance building material that combines positive aspects of fresh properties of self-compacting concrete (SCC) with improved characteristics of hardened concrete as a result of fibre addition. To produce SCC, either the constituent materials or the corresponding mix proportions may notably differ from the conventional concrete (CC). These modifications besides enhance the concrete fresh properties affect the hardened properties of the concrete. Therefore, it is vital to investigate whether all the assumed hypotheses about CC are also valid for SCC structures. In the present paper, the experimental results of short-term flexural load tests on eight reinforced SCC and FRSCC specimens slabs are presented. For this purpose, four SCC mixes - two plain SCC, two steel, two polypropylene, and two hybrid FRSCC slab specimens - are considered in the test program. The tests are conducted to study the development of SCC and FRSCC flexural cracking under increasing short-term loads from first cracking through to flexural failure. The achieved experimental results give the SCC and FRSCC slabs bond shear stresses for short-term crack width calculation. Therefore, the adopted bond shear stress for each mix slab is presented in this study. Crack width, crack patterns, deflections at mid-span, steel strains and concrete surface strains at the steel levels were recorded at each load increment in the post-cracking range.

• 대한토목학회논문집
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• 제29권5A호
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• pp.531-541
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• 2009

본 연구에서는 강도수준(30, 50 및 70 MPa)에 따른 고유동 자기충전 콘크리트의 수화발열 특성을 알아보기 위하여 2성분계 및 3성분계 고유동 자기충전 콘크리트를 제조하여 일반콘크리트와 수화열, 응결 및 역학적 특성을 분석 고찰 하였으며, 콘크리트에 사용된 분체에 대한 미소수화열량을 측정하여 얻은 분체의 열특성값, 간이단열온도실험을 실시하여 얻은 콘크리트의 열특성값 및 콘크리트에 사용된 재료의 일반적인 열특성값을 간편한 방법의 추정식을 이용하여 콘크리트 단열온도를 추정하였다. 또한, 온도해석에 의하여 얻어진 수화열 및 단열온도 특성값을 MIDAS CIVIL 06 프로그램을 이용하여 3차원 온도응력 해석을 실시하여 고유동 자기충전 콘크리트의 수화발열 특성 및 수화열에 의한 온도응력을 분석 고찰하였다.

• Advances in concrete construction
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• 제7권2호
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• pp.87-96
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• 2019

Self-compacting concretes (SCC) are highly fluid concrete which can flow without any vibration. Their composition requires a large quantity of fines to limit the risk of bleeding and segregation. The use of crushed sand rich in limestone fines could be an adequate solution for both economic and environmental reasons. This paper investigates the influence of quarry limestone fines from manufactured crushed sand on rheological, mechanical and durability properties of SCC. For this purpose, five mixtures of SCC with different limestone fines content as substitution of crushed sand (0, 5, 10, 15 and 20%) were prepared at constant water-to-cement ratio of 0.40 and $490kg/m^3$ of cement content. Fresh SCC mixtures were tested by slump flow test, V-funnel flow time test, L-box height ratio, segregation resistance and rheological test using a rheometer. Compressive and flexural strengths of SCC mixtures were evaluated at 28 days. Regarding durability properties, total porosity, capillary water absorption and chloride-ion migration were studied at 180 days. For the two test modes in fresh state, the results indicated compatibility between slump flow/yield stress (${\tau}_0$) and V-funnel flow time/plastic viscosity (${\mu}$). Increasing the substitution level of limestone fines in SCC mixtures, contributes to the decrease of the slump flow and the yield stress. All SCC mixtures investigated achieved adequate filling, adequate passing ability and exhibit no segregation. Moreover, the inclusion of limestone fines as crushed sand substitution reduces the capillary water absorption, chloride-ion migration and consequently enhances the durability performance.

• Computers and Concrete
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• 제18권5호
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• pp.969-982
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• 2016

This paper investigates the compressive fatigue behaviour of polypropylene fibre reinforced self compacting concrete with Granite Sawing Waste (GSW). An experimental programme was conducted to obtain the fatigue lives of fibre reinforced self compacting concrete (FRSCC) at various stress levels. The stress ratio was kept constant as 0.3. Compressive fatigue test was conducted on 60 cubic specimens with 100mm edge length and 0.1% of polypropylene fibres at a frequency of 0.05Hz. The test results indicate that the fatigue lives of concretes containing granite sawing waste follow the double-parameter Weibull distribution. The fatigue strength equations have been developed based on different probabilities of failure.

• 콘크리트학회논문집
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• 제25권6호
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• pp.657-665
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• 2013

이 연구는 알칼리 활성 슬래그(alkali-activated slag, AAS) 결합재를 이용하여 자기충전성을 갖는 콘크리트 개발을 위한 기초 연구로서 자기충전 콘크리트에 사용될 AAS 결합재 및 고성능 감수제의 유동성능 평가를 통해 선정하고, 선정된 결합재 및 고성능 감수제를 사용하여 자기충전 콘크리트를 배합한 후 굳기 전 콘크리트의 유동특성을 평가하였다. 높은 pH에서 폴리카르본산계 고성능 감수제의 성능이 저하됨에 따라 비교적 강도가 낮은 약알칼리성 활성화제를 사용한 AAS 결합재를 선정하였다. 시험 결과 일본토목학회(JSCE) 기준인 고유동성, 재료분리 저항성, 간극 충전성은 대부분 만족시켰으나, AAS 페이스트의 기본점성이 OPC에 비해 높은 이유로 유럽통합기준의 간극 통과성은 만족시키지 못했다. 하지만, AAS 결합재를 이용하면 증점제의 사용 없이 재료분리가 발생되지 않는 자기충전 콘크리트 제조가 가능함을 확인하였다. 이 연구는 AAS 결합재를 이용한 자기충전 콘크리트 개발의 기초연구로서 앞으로 현장적용이 가능한 AAS 자기충전 콘크리트 개발을 위해 더 높은 강도의 고유동 결합재와 간극 통과성을 높이기 위한 콘크리트 배합비의 연구가 필요하다.

• 콘크리트학회지
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• 제18권4호
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• pp.68-72
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• 2006

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2008년도 추계 학술발표회 제20권2호
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• pp.365-368
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• 2008

최근, 하천에서 얻을 수 있는 자연모래의 부족과 환경 보호에 대한 요구 등으로 인해 잔골재로써의 부순 모래가 콘크리트 산업에서 사용이 증가되고 있다. 골재는 자기충전 모르타르(SCM)를 포함한 자기 충전 콘크리트(SCC)의 특성에 큰 영향을 준다. 잔골재로 부순 모래를 사용한 SCC와 SCM의 유동적 특성을 자연 모래를 사용한 것과 두 가지를 섞은 모래를 사용한 SCC와 SCM과 비교 하였다. 실험결과는 50% 섞인 모래가 포함된 SCM의 yield stress가 SP 함유량에 따른 자연 모래와 부순 모래보다 높다는 것을 보여준다. 자연모래 SCC의 슬럼프 값은 부순 모래의 SCC보다 거의 5-15% 높다. 또한 같은 물/시 멘트비와 증점제에서 자연모래 SCC의 L-box test 값은 부순 모래 SCC보다 거의 20-30% 높다.

• Geomechanics and Engineering
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• 제34권5호
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• pp.473-480
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• 2023

Acid rain of soils has a significant impact on mechanical properties. An X-ray diffraction test, scanning electron microscope (SEM) test, laser particle size analysis test, and triaxial unconsolidated undrained (UU) test were carried out in red clay soils with different compaction degrees under the effect of different concentrations of acid. The experiments demonstrated that: the dissolution effect of acid rain on colluvium weakened with the increase in the compacting degree under the condition of certain pH values, i.e., the damage to the structure of red clay soil was relatively light, where the number of newly increased pores in the soil decreased and the agglomeration of soil particles increased; for the same compacting degree, the structural gap decreased, and the agglomeration increased with the increase in the pH value (acidity decreases) of the acid rain; the dissolution rate of Si, Al, Fe, and other elemental minerals and cement in red clay soil was found to be higher under the effect of acid rain, in turn destroying the original structure of the soil body and producing a large number of pores. This is macroscopically expressed as the decrease of the soil cohesion and internal friction angle, thereby reducing the shear strength of the soil body.

• 콘크리트학회논문집
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• 제26권3호
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• pp.277-285
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• 2014

이 연구는 현장에서 사용하는 재료의 품질 및 계량오차, 현장조건 등에 따라 병용계 자기충전 콘크리트의 유동특성에 영향을 미치는 변동요인의 범위를 실험적으로 규명하기 위한 것이다. 병용계 자기충전 콘크리트의 재료는 벨라이트 시멘트와 석회석 미분말을 사용한 벨라이트계 및 슬래그 시멘트와 석회석 미분말을 사용한 슬래그계가 선정되었으며, 선행연구에서 제시된 최적배합 조건을 대상으로 하였다. 변동요인으로 (1) 콘크리트의 온도 3종류, (2) 잔골재의 표면수율 5종류, (3) 잔골재의 조립률 5종류, (4) 고성능AE감수제의 사용량 5종류, (5) 석회석 미분말의 분말도 3종류 등을 대상으로 민감도 시험을 실시하였다. 민감도 시험의 항목은 슬럼프 플로우, 500 mm 플로우 도달시간, V-깔대기 유하시간, U-box 충전성 높이를 대상으로 하였다. 실험 결과, (1) 콘크리트 온도는 $10{\sim}20^{\circ}C$ 범위, (2) 잔골재의 표면수율은 ${\pm}0.6%$ 범위, (3) 잔골재의 조립률 $2.6{\pm}0.2$ 범위, (4) 고성능AE감수제의 사용량은 ${\pm}0.2%$ 범위, (5) 석회석 미분말의 분말도는 $6000cm^2/g$ 범위에서 현장품질을 관리해야 한다. 벨라이트계 및 슬래그계에 따른 차이는 크지 않았지만, 석회석 미분말 및 $C_2S$ 함량이 높은 벨라이트계가 안정적인 경향을 나타내었다. 따라서 이러한 결과를 현장 시공현장에서 병용계 자기충전 콘크리트의 관리방안으로 제안하고자 한다.