• 한국지반공학회논문집
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• 제29권1호
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• pp.71-80
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• 2013

2가지 시공법(즉 선단분출형슈방식, 선행굴착방식)으로 시공한 무소음 무진동을 위한 스크류콘크리트말뚝의 인접지반에서 시공 전 후 및 11개월 경과 시 원위치시험(CPT, SPT)을 실시하였다. 선단분출형슈방식 시공법의 경우 시공 직후 말뚝 중심~3.5D(여기서 D : 말뚝직경)의 영역에 있는 지반의 강도는 원지반 강도의 46%정도로 크게 감소하였으며 시공 후 약 11개월 경과 시 말뚝 인접 지반의 강도회복은 원 지반 강도의 71%정도로 나타났다. 선행굴착방식 시공법의 경우 11개월 경과 시 말뚝 인접 지반의 강도는 원지반의 전단강도까지 회복되는 것으로 나타났다.

• 콘크리트학회논문집
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• 제14권5호
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• pp.698-707
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• 2002

본 연구에서는 건축물에 발생된 화재와 같이 단기간에 빠르게 가열되는 조건하에 고강도 콘크리트의 압축강도특성을 구명하기 위하여 기존의 내화실험결과를 수집 및 분석하며 아울러 현행 노출온도에 따른 압축강도의 상관관계 기준식의 고강도 콘크리트에 적용 가능성을 검토하고자 한다. 노출온도에 따른 고강도 콘크리트의 압축강도 변화 특성은 내화실험방법(재하, 비재하 및 비재하 잔여 강도실험) 및 골재종류(천연 및 경량골재)에 따라 다르게 나타나므로 실험방법 및 골재종류별로 나누어 비교 및 분석하였다. 고강도 콘크리트의 압축강도 특성은 보통강도와는 노출온도에 따라 다르게 나타났으며 노출온도 약 2$0^{\circ}C$에서 40$0^{\circ}C$범위에서 보통강도 콘크리트보다 급격하게 압축강토가 저하되었으며 40$0^{\circ}C$ 이상에서는 큰 차이를 보이지 않았다. 80$0^{\circ}C$에서 고강도 콘크리트의 압축강도는 상온 압축강도의 30%까지 감소되었다. 노출온도에 따른 압축강도 및 탄성계수 변화에 대한 실험결과와 유럽 기준을 비교하여 볼 때 현행 기준식은 안전측이지 못하므로 화재에 노출된 고강도 콘크리트의 압축강토 및 탄성계수 평가에 적응 가능성이 결여된 것으로 평가되었다.

• 대한안전경영과학회지
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• 제9권4호
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• pp.83-90
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• 2007

This study is to find out if it can be recycled for making better concrete. Therefore, waste paper as of newspaper and newspaper are added into concrete to see if waste paper-mixing concrete can have any particular characteristic. The test result of paper concrete was compared and analyzed through four kinds of tests such as compressive strength as of a fundamental one of concrete resistant capacity against heat. $200^{\circ}C,\;400^{\circ}C\;and\;600^{\circ}C$ heated concrete were compressively tested in order to find out concrete strength resistant to high temperature. heat capacity was also tested, based on the expectancy of its low conductivity. finally flexural strength test using four reinforced concrete beams with size of $20cm{\times}30cm{\times}160cm$ was made. And concrete property exposed to the temperature showed that there are almost not effect for the strength up to $400^{\circ}C$, but it was decreased down to 50% of the original condition. volume of paper mixed with concrete without relation to paper kinds of new and waste one.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2002년도 봄 학술발표회 논문집
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• pp.997-1002
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• 2002

Traditional prediction models have been developed with a fixed equation form based on the limited number of data and parameters. If new data is quite different from original data, then the model should update not only its coefficients but also its equation form. However, artificial neural network (ANN) does not need a specific equation form. Instead of that, it needs enough input-output data. Also, it can continuously re-train the new data, so that it can conveniently adapt to new data. Therefore, the purpose of this paper is to develop the I-PreConS (Intelligent system for PREdiction of CONcrete Strength using ANN) that provides in-place strength information of the concrete to facilitate concrete form removal and scheduling for construction.

• Structural Engineering and Mechanics
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• 제23권1호
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• pp.43-61
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• 2006

An investigation of the effectiveness of the interface treatment when column concrete jacketing is performed is presented. Alternative methods of interface connection were used in order to investigate the performance of strengthened concrete columns. These connecting techniques involved roughening the surface of the original column, embedding steel dowels into the original column and a combination of these two techniques. The experimental program included three strengthened specimens, one original specimen (unstrengthened) and one as-built specimen (monolithic). The specimens represented half height full-scale old Greek Code (1950's) designed ground floor columns of a typical concrete frame building. The jackets of the strengthened specimens were constructed with shotcrete. All specimens were subjected to displacement controlled earthquake simulation loading. The seismic performance of the strengthened specimens is compared to both the original and the monolithic specimens. The comparison was performed in terms of strength, stiffness and hysteretic response. The results demonstrate the effectiveness of the strengthening methods and indicate that the proper construction of a jacket can improve the behaviour of the specimens up to a level comparable to monolithic behaviour. It was found that different methods of interface treatment could influence the failure mechanism and the crack patterns of the specimens. It was also found that the specimen that combined roughening with dowel placement performed the best and all strengthened columns were better at dissipating energy than the monolithic specimen.

• Advances in concrete construction
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• 제9권1호
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• pp.9-22
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• 2020

The present work looks at the possibilities of recycling more than once demolished concrete as coarse aggregates, to produce new concrete. Different concrete mixes were made with substitutions of 50%, 75% and 100% of recycled concrete aggregates respectively as coarse aggregates. The physico-mechanical characterization tests carried out on the recycled concrete aggregates revealed that they are suitable for use in obtaining a structural concrete. The resulting concrete materials had rheological parameters, compressive strengths and tensile strengths very slightly lower than those of the original concrete even when 100% of two cycles recycled concrete aggregates were used. The durability of the recycled aggregates concrete was assessed through water permeability, water absorption and chemical attacks. The obtained concretes were thought fit for use as structural materials. A linear regression was developed between the strength of the material and the number of cycles of concrete recycling to anticipate the strength of the recycled aggregates concrete. From the results, it appear clear that recycling demolished concrete represents a valuable resource for aggregates supply to the concrete industry and a the same time plays a key role in meeting the challenge for a sustainable development.

• International Journal of Concrete Structures and Materials
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• 제8권4호
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• pp.309-313
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• 2014

The volume fraction of the coarse aggregate in the conventional plastic concrete is controlled relatively low to ensure a required workability. In this paper, a new type of coarse aggregate interlocking concrete with strength ranging from C30 to C80 was prepared with scattering-filling aggregate process. The strength of concrete prepared with this method increases obviously whereas the shrinkage decreases significantly, the cement dosage in the concrete decreased 20 % at the same time. The microhardness of the ITZ between the cement paste and scattering-filling aggregate is higher than that of the original aggregate, the ITZ become narrower and tighter also. The interlocking and more even distribution of the coarse aggregate and the water absorption of the addition of extra amount of coarse aggregates contribute to the strength and performance improvement of the concrete prepared with scattering-filling aggregate process.

• International Journal of Concrete Structures and Materials
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• 제6권3호
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• pp.199-207
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• 2012

Concrete is an economical construction material and for that reason it is widely used in buildings and infrastructures. The use of deicing salts, expansion joint failure, and freeze-thaw cycles have led to concrete bridge girders experiencing corrosion of steel reinforcement and becoming unsafe for driving. The goal of this research is to assess the effectiveness of current and possible repair techniques for the end region of damaged prestressed concrete girders. To do this, three American Association of State Highway and Transportation prestressed concrete girders were tested to failure, repaired, and retested. Three different repair materials were tested including carbon fiber, glass fiber, and surface mounted rods. Each different repair material was also tested with and without injected epoxy. Comparisons were then made to determine if injecting epoxy had a positive effect on stiffness and strength recovery as well as which repair type regained the largest percentage of original strength.

• Earthquakes and Structures
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• 제17권1호
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• pp.115-129
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• 2019

The effectiveness of an innovative method for the earthquake-resistant rehabilitation of existing poorly detailed reinforced concrete (RC) structures is experimentally investigated herein. Eight column subassemblages were subjected to earthquake-type loading and their hysteretic behaviour was evaluated. Four of the specimens were identical and representative of columns found in RC structures designed in the 1950s-70s period for gravity load only. These original specimens were subjected to cyclic lateral deformations and developed brittle failure mechanisms. Three of the damaged specimens were subsequently retrofitted with innovative high-strength steel fiber-reinforced concrete (HSSFC) jackets. The main variables examined were the jacket width and the contribution of mesh steel reinforcement in the seismic performance of the enhanced columns. The influence of steel fiber volume fraction was also examined using test results of a previous work of Tsonos et al. (2017). The fourth earthquake damaged subassemblage was strengthened with a conventional RC jacket and was subjected to the same lateral displacement history as the other three retrofitted columns. The seismic behaviour of the subassemblages strengthened according to the proposed retrofit scheme was evaluated with respect to that of the original specimens and that of the column strengthened with the conventional RC jacket. Test results clearly demonstrated that the HSSFC jackets effectively prevented the development of shear failure mechanisms, while ensuring a ductile seismic response similar to that of the subassemblage retrofitted with the conventional RC jacket. Ultimately, an indisputable superiority in the overall seismic performance of the strengthened columns was achieved with respect to the original specimens.

• Computers and Concrete
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• 제28권6호
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• pp.585-603
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• 2021

The validation based on the experimental data demonstrates that the concrete strength under triaxial compression (TC) is overestimated by Lubliner-Oller strength criterion (SC) but underestimated by Lubliner-Lee SC in ABAQUS. Moreover, the discontinuous derivatives of failure criterion exists near the unexpected breakpoints. Both resulted from the piecewise linear meridians of the original Lubliner SC with constants γ. Following the screen for the available failure criteria to determine the model parameter γ of Lubliner SC, Menétrey-Willam SC (MWSC) is considered the most promising option with a reasonable aspect ratio Kc but no other strength values required and only two new model parameters introduced. The failure surface of the new Lubliner SC based on MWSC (Lubliner-MWSC) is smooth and has no breakpoints along the hydrostatic pressure (HP) axis. Finally, predicted results of Lubliner-MWSC are compared with other concrete failure criteria and experimental data. It turns out that the Lubliner-MWSC can represent the concrete failure behavior, and MWSC is the optimal choice to improve the applicability of the concrete damaged plasticity model (CDPM) under TC in ABAQUS.