• Computers and Concrete
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• 제27권4호
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• pp.333-341
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• 2021

Steel slag, an industrial reject from the steel rolling process, has been identified as one of the suitable, environmentally friendly materials for concrete production. Given that the coarse aggregate portion represents about 70% of concrete constituents, other economic approaches have been found in the use of alternative materials such as steel slag in concrete. Unfortunately, a standard framework for its application is still lacking. Therefore, this study proposed functional model equations for the determination of strength properties (compression and splitting tensile) of steel slag aggregate concrete (SSAC), using gene expression programming (GEP). The study, in the experimental phase, utilized steel slag as a partial replacement of crushed rock, in steps 20%, 40%, 60%, 80%, and 100%, respectively. The predictor variables included in the analysis were cement, sand, granite, steel slag, water/cement ratio, and curing regime (age). For the model development, 60-75% of the dataset was used as the training set, while the remaining data was used for testing the model. Empirical results illustrate that steel aggregate could be used up to 100% replacement of conventional aggregate, while also yielding comparable results as the latter. The GEP-based functional relations were tested statistically. The minimum absolute percentage error (MAPE), and root mean square error (RMSE) for compressive strength are 6.9 and 1.4, and 12.52 and 0.91 for the train and test datasets, respectively. With the consistency of both the training and testing datasets, the model has shown a strong capacity to predict the strength properties of SSAC. The results showed that the proposed model equations are reliably suitable for estimating SSAC strength properties. The GEP-based formula is relatively simple and useful for pre-design applications.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1995년도 봄 학술발표회 논문집
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• pp.225-230
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• 1995

Concrete structures need repair and rehabilitation due to functional deficiencies such as cracks, scaling and spalling. Loss of section such as spalling is caused by corrosion of reinforcing bar, fire, temperature change, poor design and etc. This study aims to examine the characteristics of polymer(epoxy)and polymer-cement(latex) for repair materials and to provide the proper repair scheme through static and fatigue tests. Totally 12 beams were tested. Results from static and fatigue tests of beams repaired with polymer and polymer-cement were compared.

• Computers and Concrete
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• 제14권5호
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• pp.563-575
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• 2014

Concrete which is a composite material is frequently used in construction works. Properties and behavior of concrete are significant under the effect of different loading cases. Impact loading which is a sudden dynamic one may have destructive effects on structures. Testing apparatuses are designed to investigate the impact effect on test members. Artificial Neural Network (ANN) is a computational model that is inspired by the structure or functional aspects of biological neural networks. It can be defined as an emulation of biological neural system. In this study, impact parameters as acceleration and impact force values of a reinforced concrete slab are obtained by using a testing apparatus and essential test devices. Afterwards, ANN analysis which is used to model different physical dynamic processes depending on several variables is performed in the numerical part of the study. Finally, test and predicted results are compared and it's seen that ANN analysis is an alternative way to predict the results successfully.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2008년도 춘계 학술발표회 제20권1호
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• pp.173-176
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• 2008

콘크리트에서 발생하는 균열 및 손상을 평가하기 위해 많은 연구가 이루어지고 있으며, 주요 콘크리트 부재(Element)에 균열이 발생하면 LED가 동작하는 스위칭(Switching) 개념의 기능성 콘크리트에 대한 연구도 진행 중이다. 이러한 자가 진단형(Type of Self-diagnostic) 시스템은 관리자가 모니터링을 통하여 교량 등의 구조물을 관리하는 데 편리성을 주지만, 보행자나 운전자들에게 갑작스런 LED점등으로 구조물에서 발생하는 손상신호(Signal Damage)의 전달이 미비하게 될 가능성도 배제할 수 없다. 따라서, 이러한 문제를 해결하기 위한 방법으로 주요 부재에 균열 및 손상이 발생하면 LED가 소등되어 보행자 및 운전자가 위험을 인지하게 되는 시스템을 구상하게 되었다. 이를 이용하면 주요 부재에 균열이 발생하여 콘크리트 내부의 센서를 파괴하여 센서 내부의 전선이 단전되어 야간 및 악천후시 가로등 및 신호기 등이 소등되어 위험을 알리는 스마트 콘크리트를 개발할 수 있기 때문에 이에 대한 연구를 구상하였다. 또한, 외력에 의해 발생한 균열 손상에 의해 센서내부의 전선이 신장(Elongation)되어 할렬될 때의 저항변화를 검토하여 관리자가 주요 부재의 손상을 검토할 수 있는 기능성 콘크리트를 개발하기 위한 기초적 연구이다.

• 한국구조물진단유지관리공학회 논문집
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• 제18권6호
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• pp.50-59
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• 2014

본 논문에서는 경북 구미시 봉곡천에 최근 건설된 다기능어도를 대상으로 SAP2000으로 구조 해석하기 위한 변수를 R/C Slab, R/C+S/C Slab 및 지하이동통로 규격(가로${\times}$세로)을 $1m{\times}0.2m$, $1m{\times}0.4m$, $1m{\times}0.6m$와 유속 0.8m/s, 1.2m/s, 1.6m/s으로 구분하여 해석한 결과와 봉곡천 설계식을 비교하여 안정성을 검토하였다. 봉곡천의 설계식 보다 R/C+S/C Slab 타입이 지하이동통로 출구부는 휨모멘트와 최대응력은 각각 28~54%, 26~50%, 측벽은 24~47%, 17~31%, 상부슬래브인 경우도 10~27%, 4~20% 적게 나타났다. 따라서 최대응력과 휨모멘트가 R/C+S/C Slab 타입이 구조 안정성이 확보되는 것으로 나타났기 때문에 지하통로는 휨모멘트와 최대 응력이 27%, 25%, 측벽은 24%, 15% 상부슬래브는 14%, 10%의 보완이 요구되는 것으로 판단된다. 이러한 결과는 지하이동통로 규격이 봉곡천 규격과 동일한 $1m{\times}0.4m$일 때가 $1m{\times}0.2m$, $1m{\times}0.6m$ 보다 안정성이 가장 유리한 것으로 확인되었다. 또한 해석 및 분석 결과를 근거로 다기능어도 시공 시 기본 자료로 활용이 기대된다.

• 한국구조물진단유지관리공학회 논문집
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• 제19권6호
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• pp.29-36
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• 2015

본 연구에서는 유황을 폴리머화하여 콘크리트 표면보호재로 활용가능성을 검토하기 위하여 내구성능 및 생물독성 평가를 실시하였다. 평가 결과, 콘크리트 표면보호재의 내화학성능은 산, 알칼리 용액에 대하여 화학저항성이 우수한 것으로 나타났다. 배합조건별 촉진내후성 실험 후 부착강도평가 결과 규사분말 및 플라이애시를 동시에 혼합한 배합에서 가장 우수한 강도특성을 나타내었다. 콘크리트용 표면보호재 시험체의 온냉반복 후에도 모든 배합조건에서 부착강도 1 MPa을 상회하였고, SFS배합에서 가장 높은 부착강도를 나타내었다. 표면보호재를 도포한 콘크리트의 촉진탄산화 및 염소이온침투저항성을 검토한 결과, 규사분말을 채움재로 사용한 표면보호재를 도포한 시험체에서 가장 우수한 내구성능을 나타내었다. 유황폴리머를 콘크리트 표면보호재로 사용시 생물독성 검토를 위해 어독성 실험을 수행한 결과, 유황폴리머는 생물에 미치는 영향은 없는 것으로 나타났다. 표면보호재의 내화학성, 동결융해저항성, 탄산화, 염소이온침투저항성 등을 모두 고려하여 볼 때, 본 연구범위에서는 유황폴리머에 채움재로서 규사분말과 플라이애시를 각각 20%씩 대체하는 것이 적절한 수준인 것으로 판단된다.

• Nuclear Engineering and Technology
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• 제47권7호
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• pp.884-894
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• 2015

Background: Fibers in concrete resist the growth of cracks and enhance the postcracking behavior of structures. The addition of fibers into a conventional reinforced concrete can improve the structural and functional performance of safety-related concrete structures in nuclear power plants. Methods: The influence of fibers on the ultimate internal pressure capacity of a prestressed concrete containment vessel (PCCV) was investigated through a comparison of the ultimate pressure capacities between conventional and fiber-reinforced PCCVs. Steel and polyamide fibers were used. The tension behaviors of conventional concrete and fiber-reinforced concrete specimens were investigated through uniaxial tension tests and their tension-stiffening models were obtained. Results: For a PCCV reinforced with 1% volume hooked-end steel fiber, the ultimate pressure capacity increased by approximately 12% in comparison with that for a conventional PCCV. For a PCCV reinforced with 1.5% volume polyamide fiber, an increase of approximately 3% was estimated for the ultimate pressure capacity. Conclusion: The ultimate pressure capacity can be greatly improved by introducing steel and polyamide fibers in a conventional reinforced concrete. Steel fibers are more effective at enhancing the containment performance of a PCCV than polyamide fibers. The fiber reinforcementwas shown to bemore effective at a high pressure loading and a lowprestress level.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2005년도 추계 학술발표회 제17권2호
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• pp.583-586
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• 2005

Strength of concrete is very important factor in design and quality management and may represent overall quality of concrete. Such strength of concrete may differ depending on amount of cement mixed, water and fine aggregate ratio. Classic concrete products have been produced mainly with ordinary portland cement(hereinafter 'cement'), water and fine aggregate as shown above, but various additives and mixture materials have been used for concrete manufacturing, along with development of high functional concrete and diversification of structures. Various kinds of chemical mixtures agents and mixture materials have been used as it requires concretes with other features which cannot be solved with existing materials only, such as high strength, high flexibility and no-separation in the water. Such addition of various mixture agents may cause change in cement hydrate, affecting strength. Hydration of cement is the process of producing potassium hydroxide, C-S-H, C-A-H and Ettringite, while causing heat generation reaction after it is mixed with water, and generation amounts of such hydrates play lots of roles in condensation and hardening. This study aims to analyze its strength and features with hydrates by making specimen according to curing temperature, types of mixture agent, mixing ratio and ages and by analyzing such hydrates in order to analyze role of cement hydrate on early strength of concrete.

• International Journal of Railway
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• 제6권2호
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• pp.59-63
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• 2013

The purpose of this paper was to evaluate the effectiveness of geogrid for conventional ballasted track and asphalt concrete underlayment track using PLAXIS finite element program. Geogrid element was modeled at various locations that include subballast/subgrade, subballast/ballast interfaces, middle of the ballast, and one-third depth of the ballast. The results revealed that the effectiveness of geogrid reinforcement appeared to be larger for ballasted track structure compared to asphalt concrete underlayment track. Particularly, in case of installing geogrid at one-third depth of ballast layer in a conventional ballasted track, the most effectiveness of geogrid reinforcement was achieved. The influence of geogrid axial stiffness on track substructure response was not clear to conclude. Further validations using a discrete element method along with experimental investigation are considered as a future study. The effect of asphalt concrete layer modulus was evaluated. The results exhibited that higher layer modulus seems to be effective in controlling displacement and strain of track substructure. However it also yields slightly higher stresses within track substructure. It infers that further validations are required to come up with optimum asphalt concrete mixture design to meet economical and functional criteria.

• 대한건축학회논문집:계획계
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• 제34권7호
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• pp.59-68
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• 2018

Salk Institute for Biological studies is widely considered as architectural masterpiece of Louis Kahn's. Its iconic plaza with symmetrical concrete structures, overlooking the Pacific ocean in La Jolla, has been acclaimed as a facade to the sky. Little has been written on Kahn's achievements in the building system integration in order to bridge the gap between technology and design. This paper explores the technical issues, the design intents, and the major building systems to identify the Kahn's integration methods between building systems. The project is analysed into four major systems; structure, mechanical, envelope, and interior system. The integration methods of building systems are investigated in physical, visual, and functional aspects. The most distinguished cases of building system integration are the introduction of the interstitial floors between the laboratories and the creation of the smooth and warm materiality of exposed concrete walls. Kahn proposed open floor plans for the laboratories which are capable of easily adapting to changing needs. He also introduced the interstitial floors which are framed of the vierendeel truss systems and deliberately overlapped the structure systems with the mechanical systems such as ducts, water pipes, and electric conduits. The exposed concrete walls mixed with pozzolan ashes look very much like granite or limestone as the result of the physical and visual integration between structure, envelope, and interior systems.