Compressive resistance behavior of UHPFRC encased steel composite stub column

Zhenyu Huang,Xinxiong Huang,Weiwen Li,Jiasheng Zhang 국제구조공학회 2020 Steel and Composite Structures, An International J Vol.37 No.2

To explore the feasibility of eliminating the longitudinal rebars and stirrups by using ultra-high-performance fiber reinforcement concrete (UHPFRC) in concrete encased steel composite stub column, compressive behavior of UHPFRC encased steel stub column has been experimentally investigated. Effect of concrete types (normal strength concrete, high strength concrete and UHPFRC), fiber fractions, and transverse reinforcement ratio on failure mode, ductility behavior and axial compressive resistance of composite columns have been quantified through axial compression tests. The experimental results show that concrete encased composite columns with NSC and HSC exhibit concrete crushing and spalling failure, respectively, while composite columns using UHPFRC exhibit concrete spitting and no concrete spalling is observed after failure. The incorporation of steel fiber as micro reinforcement significantly improves the concrete toughness, restrains the crack propagation and thus avoids the concrete spalling. No evidence of local buckling of rebars or yielding of stirrups has been detected in composite columns using UHPFRC. Steel fibers improve the bond strength between the concrete and, rebars and core shaped steel which contribute to the improvement of confining pressure on concrete. Three prediction models in Eurocode 4, AISC 360 and JGJ 138 and a proposed toughness index (T.I.) are employed to evaluate the compressive resistance and post peak ductility of the composite columns. It is found that all these three models predict close the compressive resistance of UHPFRC encased composite columns with/without the transverse reinforcement. UHPFRC encased composite columns can achieve a comparable level of ductility with the reinforced concrete (RC) columns using normal strength concrete. In terms of compressive resistance behavior, the feasibility of UHPFRC encased steel composite stub columns with lesser longitudinal reinforcement and stirrups has been verified in this study.

Novel nonlinear stiffness parameters and constitutive curves for concrete

Rajai Z. Al-Rousan,Mohammed A. Alhassan,Moheldeen A. Hejazi 사단법인 한국계산역학회 2018 Computers and Concrete, An International Journal Vol.22 No.6

Concrete is highly non-linear material which is originating from the transition zone in the form of micro-cracks, governs material response under various loadings. In this paper, the constitutive models published by many researchers have been used to generate novel stiffness parameters and constitutive curves for concrete. Following such linear material formulations, where the energy is conservative during the curvature, and a nonlinear contribution to the concrete has been made and investigated. In which, nonlinear concrete elastic modulus modeling has been developed that is capable-of representing concrete elasticity for grades ranging from 10 to 140 MPa. Thus, covering the grades range of concrete up to the ultra-high strength concrete, and replacing many concrete models that are valid for narrow ranges of concrete strength grades. This has been followed by the introduction of the nonlinear Hooke’s law for the concrete material through the replacement of the Young constant modulus with the nonlinear modulus. In addition, the concept of concrete elasticity index (φ) has been proposed and this factor has been introduced to account for the degradation of concrete stiffness in compression under increased loading as well as the multi-stages micro-cracking behavior of concrete under uniaxial compression. Finally, a sub-routine artificial neural network model has been developed to capture the concrete behavior that has been introduced to facilitate the prediction of concrete properties under increased loading.

Prediction of fly ash concrete compressive strengths using soft computing techniques

Rajeshwari Ramachandra,Sukomal Mandal 사단법인 한국계산역학회 2020 Computers and Concrete, An International Journal Vol.25 No.1

The use of fly ash in modern-day concrete technology aiming sustainable constructions is on rapid rise. Fly ash, a spinoff from coal calcined thermal power plants with pozzolanic properties is used for cement replacement in concrete. Fly ash concrete is cost effective, which modifies and improves the fresh and hardened properties of concrete and additionally addresses the disposal and storage issues of fly ash. Soft computing techniques have gained attention in the civil engineering field which addresses the drawbacks of classical experimental and computational methods of determining the concrete compressive strength with varying percentages of fly ash. In this study, models based on soft computing techniques employed for the prediction of the compressive strengths of fly ash concrete are collected from literature. They are classified in a categorical way of concrete strengths such as control concrete, high strength concrete, high performance concrete, self-compacting concrete, and other concretes pertaining to the soft computing techniques usage. The performance of models in terms of statistical measures such as mean square error, root mean square error, coefficient of correlation, etc. has shown that soft computing techniques have potential applications for predicting the fly ash concrete compressive strengths.

높은 혼합비율의 플라이 애쉬를 갖는 콘크리트의 침투성 특징에 관한 연구

이진용 한국콘크리트학회 1995 콘크리트학회지 Vol.7 No.4

콘크리트의 침투성은 내구성과 밀접한 관계가 있고, 콘크리트의 내구성은 침투성 특성에 의해서 간접적으로 측정될 수 잇다. 실험 결과에 의하면 콘크리트의 침투성에서 플라이애쉬의 양이 증가할수록 (15%, 30%, 그리고45%) 침투성이 낮아졌으며, 기건양생한 콘크리트가 수중양생한 것에 비해서 월등히 높은 침투성을 보여 주었으나. 그 차이점은 플라이애쉬를 섞는 양이 많을수록 줄어 들었다. 높은 비율의 플라이애쉬(45%) 다양한 조강 시멘트를 섞어 만든 콘크리트에서도, 플라이애쉬 콘크리트가 보통(PCI)콘크리트보다 낮은 침투성을 보여주었다. 콘크리트는 양생기간이 길어짐에 따라 시멘트종류에 관계없이 침투성이 낮아졌으나, 기건양생시에는 증가하는 것을 보여주었다. 침투성 특징에서 모든 콘크리트는 물을 이용해 시험한 것이 기체를 이용해 시험한 것 보다 항상 낮은 값을 갖는다는 것이 발견되었다. 콘크리트의 침투성은 그것의 강도가 증가함으로써 줄어드는 것을 발견하였으나, 침투성의 특징은 주로 사용한 시멘트종류와 좀더 밀접한 관계가 있는 것으로 나타났다. The permeability of concrete is closely related to the durability and the latter may be expressed by measuring permeability of concrete. According to the results, the permeability of fly ash concrete was lower than that of OPC(PC1) concrete and decreased with increasing fly ash levels(l5%, 30% and 45%). The permeability values of concrete cured in water is significantly lower than those of concrete cured in air, but the differences were reduced with increasing fly ash level. In comparison with OPC(PC1) concrete and high fly ash concrete containing enhanced early strength cements, the latter also had a lower permeability than the former. The permeability of concrete cured in water was decreased with curing time(28 and 180 days) irrespectwe of cement types. However, the trend of results cured in air was opposite to that cured in water due to the rnicrocrackinp: of concrete. It was found that the properties of strength and permeability of concrete were related each other. However, the permeability of concrete was more dependant upon the type of binder used in concrete.

Verification of Integrated Decontamination Equipment Automation Performance to Remove Concrete Surface Contamination

Byeong-Ho Kim,Ki-Hyun Kwon,Hyeon-Oh Park 한국방사성폐기물학회 2023 한국방사성폐기물학회 학술논문요약집 Vol.21 No.1

Concrete radioactive waste is divided into surface-contaminated concrete and activated concrete, and although the generation rate varies depending on the operating conditions of the nuclear power plant, it is reported that the amount of surface-contaminated concrete generated is greater. It is reported in the ‘US-NRC Inventory Report’ that 99% of radionuclides in surface-contaminated concrete are distributed within 1 mm of the surface. Since concrete radioactive waste accounts for a large amount of generation after metal radioactive waste, it is necessary to reduce the amount of radioactive waste disposal by applying appropriate treatment techniques to surface-contaminated concrete. In this study, a similar contamination environment work space with the size of 5.4 (W) × 3.6 (L) × 2.5 (H) [m] in which concrete specimens can be fixed on the wall and floor was established. And an integrated decontamination equipment was verified the automation performance for ‘location accuracy’, ‘radioactive contamination level measurement’ and ‘concrete surface laser scabbling’. It was confirmed that the average was 8.3 [mm] in the evaluation of the ‘location accuracy’ for the remote control and movement of the integrated decontamination equipment. For performance verification of ‘radioactive contamination level measurement’ and ‘laser scabbling’, it were used that size of 30×30×8 [cm] ordinary concrete specimens and concrete radioactively contaminated with Co-60 below the regulatory exemption concentration. ‘Radioactive contamination level measurement’ is measured as much as the set range, divied and display the measured values in different colors on the map of the control program. Ordinary concrete specimens are 0.066~0.089 μ Sv/hr, and contaminated concrete specimens are 0.107~0.121 μ Sv/hr, and it was confirmed that they are expressed in different colors on the map. For ‘laser scabbling’, the performance according to the laser scabbling speed and reproducibility with ordinary concrete specimens was verified. As a result, a weight change of up to 1.48 kg was confirmed. Contaminated concrete specimens were subjected to a direct method using a surface contamination detector and an indirect method using a smear paper to measure surface contamination before and after scabbling, and the debris generated after scabbling was analyzed using HPGe.

고흡수성수지를 첨가한 콘크리트의 강도 및 마모저항성 평가

전성일,이문섭,남정희 한국도로학회 2018 한국도로학회논문집 Vol.20 No.6

PURPOSES: In this study, the effects of adding a superabsorbent polymer (SAP) to the concrete mixture on the strength of the concrete and abrasion resistance were analyzed, and whether the property of concrete can be improved by the internal curing effect of SAP was evaluated. METHODS: In this study, a total of eight different mixes were tested. The amounts of SAP added were 0%, 0.6%, 1.2% while that of silica fume were 0% and 6% based on the weight of the binder. The compressive test, rapid chloride penetration resistance test, and abrasion test were performed to verify the internal curing effects of SAP. RESULTS : The compressive test showed that SAP concrete had greater compressive strength than ordinary concrete. Comparison of the compressive strengths of dry and wet cured specimens of each mixture showed that SAP concrete had a smaller difference compared with ordinary concrete. The rapid chloride resistance test showed that SAP did not increase chloride penetration resistance. However, since this experiment only considered wet curing, further investigation of dry curing is necessary. The abrasion resistance test showed that for the case of concrete cured under dry conditions without spraying the curing compound, the abrasion resistance of the SAP concrete improved by approximately 49% at 14 days and 27% at 28 days of curing compared with ordinary concrete. CONCLUSIONS : The effect of SAP on the strength and abrasion resistance of concrete was analyzed. The results showed that the internal curing effect of SAP improved concrete strength and abrasion resistance. The internal curing effect maintains the overall internal humidity in concrete by supplying water held by the SAP to the dried cement paste.

Assessment of Mass Fraction and Melting Temperature for the Application of Limestone Concrete and Siliceous Concrete to Nuclear Reactor Basemat Considering Molten Coree-Concrete Interaction

Lee, Hojae,Cho, Jae-Leon,Yoon, Eui-Sik,Cho, Myungsug,Kim, Do-Gyeum Korean Nuclear Society 2016 Nuclear Engineering and Technology Vol.48 No.2

Severe accident scenarios in nuclear reactors, such as nuclear meltdown, reveal that an extremely hot molten core may fall into the nuclear reactor cavity and seriously affect the safety of the nuclear containment vessel due to the chain reaction caused by the reaction between the molten core and concrete. This paper reports on research focused on the type and amount of vapor produced during the reaction between a high-temperature molten core and concrete, as well as on the erosion rate of concrete and the heat transfer characteristics at its vicinity. This study identifies themass fraction and melting temperature as the most influential properties of concrete necessary for a safety analysis conducted in relation to the thermal interaction between the molten core and the basemat concrete. The types of concrete that are actually used in nuclear reactor cavities were investigated. The $H_2O$ content in concrete required for the computation of the relative amount of gases generated by the chemical reaction of the vapor, the quantity of $CO_2$ necessary for computing the cooling speed of the molten core, and the melting temperature of concrete are evaluated experimentally for the molten core-concrete interaction analysis.

초등기하 학습에서의 구체물과 반구체물 활용에 대한 연구

임영빈,홍진곤 대한수학교육학회 2016 학교수학 Vol.18 No.3

The position as saying that the math learning needs to begin from what diversely presents concrete object or familiar situation is well known as a name dubbed CSA(Concrete-Semiconcrete- Abstract). Compared to this, a recent research by Kaminski, et al. asserts that learning an abstract concept first may be more effective in the aspect of knowledge transfer than learning a mathematical concept with concrete object of having various contexts. The purpose of this study was to analyze a class, which differently applied a guidance sequence of concrete object, semi-concrete object, and abstract concept in consideration of this conflicting perspective, and to confirm its educational implication. As a result of research, a class with the application of a concept starting from the concrete object showed what made it have positive attitude toward mathematics, but wasn't continued its effect, and didn't indicate significant difference even in achievement. Even a case of showing error was observed rather owing to the excessive concreteness that the concrete object has. This error wasn't found in a class that adopted a concept as semi-concrete object. This suggests that the semi-concrete object, which was thought a non-essential element, can be efficiently used in learning an abstract concept. 수학 학습이 구체물이나 친숙한 상황을 다양하게 제시해주는 것으로부터 시작되어야 한다는 입장은 CSA(Concrete-Semiconcrete-Abstract)라는 이름으로 잘 알려져 있다. 이에 비하여 최근 Kaminski 등의 연구는, 다양한 맥락을 가진 구체물로 수학적 개념을 학습하는 것보다 추상적인 개념을 먼저 학습하는 것이 지식의 전이 측면에서 효과적일 수 있음을 주장한다. 본고에서는 이러한 상반된 관점을 고려하여, 구체물, 반구체물, 추상적 개념의 지도순서를 다르게 적용한 수업을 분석하고 그 교육적 시사점을 확인하고자 하였다. 연구 결과 구체물로 시작하여 개념을 도입한 수업은 수학에 대한 긍정적인 태도를 가지게 한 것으로 보였으나 그 효과가 지속적이지는 않았으며, 성취도 면에서도 유의미한 차이를 보이지 않았고, 오히려 구체물이 가지는 과도한 구체성으로 인해 오류를 보이는 경우가 관찰되었다. 이러한 오류는 반구체물로 개념을 도입한 수업에서는 발견되지 않았는데, 이는 비본질적 요소가 사상된 반구체물이 추상적인 개념 학습에 효율적으로 사용될 수 있음을 시사한다.

Numerical analysis of concrete degradation due to chloride-induced steel corrosion

Ayinde, Olawale O.,Zuo, Xiao-Bao,Yin, Guang-Ji Techno-Press 2019 Advances in concrete construction Vol.7 No.4

Concrete structures in marine environment are susceptible to chloride attack, where chloride diffusion results in the corrosion of steel bar and further lead to the cracking of concrete cover. This process causes structural deterioration and affects the response of concrete structures to different forms of loading. This paper presents the use of ABAQUS Finite Element Software in simulating the processes involved in concrete's structural degradation from chloride diffusion to steel corrosion and concrete cover cracking. Fick's law was used for the chloride diffusion, while the mass loss from steel corrosion was obtained using Faraday's law. Pressure generated by steel corrosion product at the concrete-steel interface was modeled by applying uniform radial displacements, while concrete smeared cracking alongside the Extended Finite Element Method (XFEM) was used for concrete cover cracking simulation. Results show that, chloride concentration decreases with penetration depth, but increases with exposure time at the concrete-steel interface. Cracks initiate and propagate in the concrete cover as pressure caused by the steel corrosion product increases. Furthermore, the crack width increases with the exposure time on the surface of the concrete.

Temperature Reduction of Concrete Pavement Using Glass Bead Materials

Erhan Burak Pancar,Muhammet Vefa Akpınar 한국콘크리트학회 2016 International Journal of Concrete Structures and M Vol.10 No.1

In this study, different proportions of glass beads used for road marking were added into the concrete samples to reduce the temperature gradient through the concrete pavement thickness. It is well known that decreasing the temperature gradient reduces the risk of thermal cracking and increases the service life of concrete pavement. The extent of alkali–silica reaction (ASR) produced with partial replacement of fine aggregate by glass bead was investigated and compressive strength of concrete samples with different proportion of glass bead in their mix designs were measured in this study. Ideal results were obtained with less than 0.850 mm diameter size glass beads were used (19 % by total weight of aggregate) for C30/37 class concrete. Top and bottom surface temperatures of two different C30/37 strength class concrete slabs with and without glass beads were measured. It was identified that, using glass bead in concrete mix design, reduces the temperature differences between top and bottom surfaces of concrete pavement. The study presented herein provides important results on the necessity of regulating concrete road mix design specifications according to regions and climates to reduce the temperature gradient values which are very important in concrete road design.