• Steel and Composite Structures
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• 제17권6호
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• pp.929-949
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• 2014

Thirty one push-out tests were carried out in order to investigate the bond behavior between shape steel, steel tube (named steels) and recycled aggregate concrete (RAC), including 11 steel reinforced recycled aggregate concrete (SRRAC) columns, 10 recycled aggregate concrete-filled circular steel tube (RACFCST) columns and 10 recycled aggregate concrete-filled square steel tube (RACFSST) columns. Eleven recycled coarse aggregate (RCA) replacement ratios (i.e., 0%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% and 100%) were considered for SRRAC specimens, while five RCA replacement ratios (i.e., 0%, 25%, 50%, 75% and 100%), concrete type and length-diameter ratio for recycled aggregate concrete-filled steel tube (RACFST) specimens were designed in this paper. Based on the test results, the influences of all variable parameters on the bond strength between steels and RAC were investigated. It was found that the load-slip curves at the loading end appeared the initial slip earlier than the curves at the free end. In addition, eight practical bond strength models were applied to make checking computations for all the specimens. The theoretical analytical model for interfacial bond shear transmission length in each type of steel-RAC composite columns was established through the mechanical derivation, which can be used to design and evaluate the performance of anchorage zones in steel-RAC composite structures.

• 한국산학기술학회논문지
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• 제18권11호
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• pp.7-15
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• 2017

본 연구에서는 콘크리트 적용 저품질 순환골재의 콘크리트 적용을 위하여 공학적 특성을 평가 하였다. 이를 위해서 저품질 순환골재의 세척유무에 따라서 골재 치환율을 30%, 60%, 100%로 콘크리트 제작하여 실험하였으며, 성능평가를 위하여 제작된 순환골재 사용 콘크리트의 압축강도, 흡수율, 표면전기저항, 초음파속도, 염소이온침투저항성 평가를 실시하였다. 세척한 저품질 순환골재의 경우 30% 치환시 천연골재와 유사한 결과를 모든 시험에서 나타내었다. 또한 60%를 치환한 콘크리트에서도 천연골재와 유사한 성능을 나타내는 것으로 확인되었다. 그러나 100%의 골재를 사용하는 것은 천연 골재 보다 다소 낮은 결과 값을 나타내었다. 반면 세척을 하지 않은 저품질 순환골재의 경우는 치환율에 관계없이 전체적으로 천연골재보다 좋지 않은 결과를 나타내었다. 특히 내구성 평가의 척도로 평가한 염소이온침투저항성 평가에서는 초기의 경우 매우 높음의 결과를 나타내었으며, 28일 재령에서도 보통 수준의 저항성을 나타내어 세척 순환골재와 약 2배 정도의 차이를 나타내었다. 따라서, 저품질 순환골재의 콘크리트 적용에 있어서 골재의 세척유무에 따라서 성능이 변화하는 것을 확인하였다.

• Computers and Concrete
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• 제16권2호
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• pp.209-222
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• 2015

This paper presents results of biaxial compressive tests and strength criterion on two replacement percentages of recycled coarse aggregate (RPRCA) by mass for plain structural recycled aggregate concrete (RAC) at all kinds of stress ratios. The failure mode characteristic of specimens and the direction of the cracks were observed and described. The two principally static strengths in the corresponding stress state were measured. The influence of the stress ratios on the biaxial strengths of RAC was also analyzed. The experimental results showed that the ratios of the biaxial compressive strength ${\sigma}_{3f}$ to the corresponding uniaxial compressive strength $f_c$ for the two RAC are higher than that of the conventional concrete (CC), and dependent on the replacement percentages of recycled coarse aggregate, stress states and stress ratios; however, the differences of tensile-compressive ratios for the two RAC and CC are smaller. On this basis, a new failure criterion with the stress ratios is proposed for plain RAC under biaxial compressive stress states. It provides the experimental and theoretical foundations for strength analysis of RAC structures subject to complex loads.

• Computers and Concrete
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• 제22권5호
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• pp.461-468
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• 2018

In this paper, to access the suitability of recycled aggregate for structural applications, concrete strength i.e., compressive, tensile and flexural strength were evaluated and compared with those specimens made of natural aggregates. Test results indicated that 30 to 42% of the mentioned strength decreases. To study the performance of frame structures made of recycled aggregate concrete (RAC) two reinforced RAC frames were prepared and tested under monotonic loading. The joint regions of one of the RAC frame were casted with micro-concrete. A reference specimen was also prepared using natural aggregate concrete (NAC) and subjected to a similar loading condition. The RAC frame resulted in a brittle mode of failure as compared to NAC frame. However, the presence of a micro-concrete at the joint region of an RAC frame improved the damage tolerance and load resisting capacity. Seismic parameter such as energy dissipation, ductility and stiffness also improves. Conclusively, strengthening of joint region using micro-concrete is found to have a significant contribution in improving the seismic performance of an RAC frame.

• Computers and Concrete
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• 제21권6호
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• pp.669-679
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• 2018

In this paper the behavior of reinforced concrete (RC) beam-column connections under cyclic loading was analyzed. The specimens, manufactured in a reduced-scale were made of (a) recycled aggregate concrete (RAC) by replacing 30% of natural coarse aggregate (NCA) with recycled coarse aggregate (RCA) and (b) RAC incorporating Polyethylene terephthalate (PET) fiber i.e., PET fiber-reinforced concrete (PFRC) at the joint region. PET fiber (aspect ratio=25) of 0.5% by weight of concrete used in the PFRC mix was obtained by hand cutting of post-consumer PET bottles. A reference specimen was also prepared using 100% of NCA and subjected to similar loading sequence. Comparing the results the structural behavior under cyclic loading of RAC specimens are quite similar to the reference specimens. Damage tolerance, load resisting capacity, stiffness degradation, ductility, and energy dissipation of the RAC specimens enhanced due to addition of PET fibers at the joint region. PFRC specimens also presented a lower damage indices and higher principal tensile stresses as compared to the RAC specimens. The results obtained gave experimental evidence on the feasibility of RAC for structural use. Using PET fibers as a discrete reinforcement is recommended for improving the seismic performance of RAC specimens.

• Computers and Concrete
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• 제16권4호
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• pp.643-667
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• 2015

3-dimentional precast recycled aggregate concrete (RAC) finite element models were developed by means of the platform OpenSees to implement sophisticated nonlinear model subjected to seismic loads. Efforts were devoted to the dynamic responses (including dynamic characteristics, acceleration amplifications, displacements, story drifts) and capacity curve. In addition, this study extended the prediction on dynamic response of precast RAC model by parametric study of material properties that represent the replacement percentage of recycled coarse aggregate (RCA). Principles and assumptions that represent characteristics of precast structure and influence of the interface between head of column and cast-in-place (CIP) joint on the stiffness of the joints was put forward and validated by test results. The comparison between simulated and tested results of the precast RAC frame shows a good correlation with most of the relative errors about 25% in general. Therefore, the adopted assumptions and the platform OpenSees are a viable approach to simulate the dynamic response of precast frames made of RAC.

• International Journal of Concrete Structures and Materials
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• 제9권3호
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• pp.337-343
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• 2015

Previous studies have shown that the drying shrinkage of recycled aggregate concrete (RAC) is greater than that of natural aggregate concrete (NAC). Drying shrinkage is the fundamental reason for the cracking of concrete, and tensile creep caused by the restraint of drying shrinkage plays a significant role in the cracking because it can relieve the tensile stress and results in the delay of cracking occurrence. However, up till now, all research has been focusing on the compressive creep of RAC. Therefore, in this study, a uniaxial restrained shrinkage cracking test was executed to investigate the tensile creep properties caused by the restraint of drying shrinkage of RAC. The mechanical properties, such as compressive strength, tensile splitting strength, and Young's modulus of RAC were also investigated in this study. The results confirmed that the tensile creep of RAC caused by the restraint of shrinkage was about 20-30 % larger than that of NAC.

• Steel and Composite Structures
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• 제9권1호
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• pp.19-38
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• 2009

The present paper provides test data to evaluate the seismic performance of recycled aggregate concrete (RAC) filled steel square hollow section (SHS) beam-columns. Fifteen specimens, including 12 RAC filled steel tubular (RACFST) columns and 3 reference conventional concrete filled steel tubular (CFST) columns, were tested under reversed cyclic flexural loading while subjected to constant axially compressive load. The test parameters include: (1) axial load level (n), from 0.05 to 0.47; and (2) recycled coarse aggregate replacement ratio (r), from 0 to 50%. It was found that, generally, the seismic performance of RACFST columns was similar to that of the reference conventional CFST columns, and RACFST columns exhibited high levels of bearing capacity and ductility. Comparisons are made with predicted RACFST beam-column bearing capacities and flexural stiffness using current design codes. A theoretical model for conventional CFST beam-columns is employed in this paper for square RACFST beam-columns. The predicted load versus deformation hysteretic curves are found to exhibit satisfactory agreement with test results.

• 한국건설순환자원학회논문집
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• 제5권1호
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• pp.85-93
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• 2017

본 연구에서는 국내에서 생산되고 있는 콘크리트용 순환 굵은골재 및 순환잔골재를 사용하여 콘크리트의 설계기준 강도(21, 35, 50MPa) 및 순환골재의 혼입조건 변화가 콘크리트의 탄산화 거동에 미치는 영향을 분석하였다. 실험결과 순환 굵은골재의 혼입률 변화에 따른 콘크리트의 슬럼프는 순환골재를 혼입하지 않은 경우에 비해 동등하거나 양호한 유동성을 나타내는 것으로 나타났으며, 순환 잔골재를 혼입한 경우는 혼입률이 증가함에 따라 슬럼프가 감소되는 결과를 나타냈다. 또한, 순환 굵은골재 및 순환 잔골재의 혼입률이 증가할수록 콘크리트의 압축강도는 감소하는 것으로 나타났으며, 순환골재 혼입률이 50%를 초과할 경우 급격한 강도 감소 경향을 나타냈다. 그리고 탄산화 깊이는 모든 순환골재 종류에서 혼입률이 증가함에 따라 최대 40%까지 증가하는 결과를 나타냈으며 낮은 강도 수준의 콘크리트 일수록 순환골재 활용에 따른 탄산화 저항성 저하 정도가 큰 것으로 나타났다. 그리고 콘크리트의 압축강도가 증가할수록 순환골재 혼입에 따른 영향은 감소되어, 고강도 영역에서는 일반 콘크리트와 유사한 탄산화 특성을 발현하는 것으로 분석되었다. 따라서 순환골재를 콘크리트용 재료로 대량 활용하기 위해서는 콘크리트의 탄산화 저항성의 개선 위한 혼화재료의 적용 또는 배합설계상 조정을 통한 강도의 개선 등이 필요할 것으로 판단된다.

• International Journal of Concrete Structures and Materials
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• 제10권1호
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• pp.61-73
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• 2016

In predicating the probability distribution of chloride diffusion coefficient of recycled aggregate concrete ($D_{RAC}$), the morphological characteristics of three phases, i.e., the old attached mortar, the natural aggregate and the new mortar, should all be taken into account. The present paper attempts to develop a probability density evolution method (PDEM) to achieve this. After verifying the derived PDEM results with experimental results, the effects of old attached mortar to the $D_{RAC}$ are examined in a quantitative manner. It is found that (1) the variation of the attached mortar content is much sensitive to $D_{RAC}$; (2) given the probability distribution of the content and chloride diffusion coefficient of old mortar, the probability distribution of DRAC can be analysed based on the PDEM; and (3) the critical chloride diffusion coefficient at a certain assurance rate can be obtained by the PDEM. The analysis results of this investigation will be valuable to the durability design for RAC.