• 한국방재학회:학술대회논문집
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• 2010.02a
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• pp.40.1-40.1
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• 2010

초고성능 콘크리트(Ultra High Performance Concrete, UHPC)는 종래의 보통 콘크리트와 다른 새로운 재료로써 높은 강도와 향상된 연성을 그 특징으로 한다. 이러한 새로운 재료의 활용을 위하여 본 연구는 초고성능 콘크리트의 부착 성능을 평가하고자 하였다. 수정된 RILEM 방법을 사용하여 초고성능 콘크리트와 이형철근의 pull-out 실험을 수행하였으며 보통 콘크리트와 비교하여 5~10배에 달하는 부착강도를 확인하였다. 또한 항복강도 400MPa급 철근에 대하여 철근 직경 2배 이상의 부착 길이에서 철근의 파단 강도에 해당하는 부착 성능을 나타내었으며 400MPa급 철근과 700MPa급 고장력 철근의 실험 결과 비교로부터 초고성능 콘크리트에서 고장력 철근 활용의 효율성을 확인하였다.

• Structural Engineering and Mechanics
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• v.54 no.6
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• pp.1201-1216
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• 2015

This paper presents the details of size independent fracture energy and bi-linear tension softening relation for nano modified high strength concrete. Nano silica in powder form has been used as partial replacement of cement by 2 wt%. Two popular methods, namely, simplified boundary effect method of Karihaloo et al. (2003) and RILEM (1985) fracture energy with P-${\delta}$ tail correction have been employed for estimation of size independent fracture energy for nano modified high strength concrete (compressive strength ranges from 55 MPa to 72 MPa). It is found that both the methods gave nearly same values, which is an additional evidence that either of them can be employed for determination of size independent fracture energy. Bi-linear tension softening relation corresponding to their size independent fracture energy has been constructed in an inverse manner based on the concept of non-linear hinge from the load-crack mouth opening plots of notched three-point bend beams.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.11a
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• pp.557-560
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• 2006

Worldwide, Certification systems for standard of material and quality of product exist very variously. Korean industrial Standard (KS) is most representatively certification systems in Korea. But laboratory of korea uses often ASTM, RILEM and JIS and these standards do not get into unionization. so, Granted that experiment is same, result still can different. Therefore, this research measured chloride amount of hardened concrete using identical material and wished to improve accuracy of chloride estimation as that comparison evaluate to each examination.

• Journal of the Korean Recycled Construction Resources Institute
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• v.5 no.3
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• pp.298-304
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• 2017

The corrosion of reinforcements embedded in concrete causes some durability problems in reinforced and prestressed concrete structures. The epoxy coated reinforcements are one of the effective and reliable methods to prevent corrosion of reinforcements. However, it has been known that the epoxy coating reduces the bond capacity of reinforcement to concrete. This paper investigates the bond behaviors of epoxy coated reinforcements experimentally using direct pull-out test. Bond behaviors of epoxy coated bars for various reinforcement diameters of 10, 19 and 29mm and thicknesses of cover concrete of 1, 2, 3, and $4.5c/d_b$ (ratio of cover to bar diameter) are examined. Total 66 specimens were manufactured and tested according to the RILEM standard method. As the diameters of the epoxy coated reinforcements increase, the difference of bond strength between epoxy coated reinforcements and uncoated bars also increases. Epoxy coated bars showed more than 85% bond performance compared to those of uncoated bars. A new formular for estimating basic development length of epoxy coated reinforcement based on equilibrium equation is proposed using this experimental result.

• International Journal of Concrete Structures and Materials
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• v.6 no.3
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• pp.187-197
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• 2012

An experimental investigation was conducted to compare the bond strength of reinforcing steel in self-consolidating concrete (SCC) with conventional concrete (CC). This study investigated two different compressive strengths of SCC as well as CC. The experimental program consisted of 24 pull-out specimens as well as 12 full-scale beams (three for each concrete type and strength). The pull-out specimens were based on RILEM recommendations, and the beam specimens were tested under a simply supported four-point loading condition. The CC test results served as a control and were used to evaluate the results from the SCC pull-out and beam specimen tests. Furthermore, a comparison was performed between results of this study and a bond database of CC specimens. These comparisons indicate that SCC beams possess comparable or slightly greater bond strength than CC beams.

• Computers and Concrete
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• v.17 no.4
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• pp.553-566
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• 2016

Fracture energy is one of the key parameters reveal cracking resistance and fracture toughness of concrete. The main purpose of this study is to determine fracture behavior, mechanical properties and microstructural analysis of high strength basalt fiber reinforced concrete (HSFRC). For this purpose, three-point bending tests were performed on notched beams produced using HSFRCs with 12 mm and 24mm fiber length and 1, 2 and $3kg/m^3$ fiber content in order to determine the value of fracture energy. Fracture energies of the notched beam specimens were calculated by analyzing load versus crack mouth opining displacement curves by the help of RILEM proposal. The results show that the effects of basalt fiber content and fiber length on fracture energy are very significant. The splitting tensile and flexural strength of HSFRC increased with increasing fiber content whereas a slight drop in flexural strength was observed for the mixture with 24mm fiber length and $3kg/m^3$ fiber content. On the other hand, there was no significant effect of fiber addition on the compressive strength and modulus of elasticity of the mixtures. In addition, microstructural analysis of the three components; cement paste, aggregate and basalt fiber were performed based on the Scanning Electron Microscopy and Energy-Dispersive X-ray Spectroscopy examinations.

• Magazine of the Korea Concrete Institute
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• v.9 no.1
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• pp.183-194
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• 1997

Traditional displacmir~nt measurement included an extrancous and cvrntlc. portmn due to test setup and support crushing. The magnitudc of this erroneous deformation was found to be of the same order as the actual displacement, leading to inaccurate determinations of fracture parameters. To overcome this problem, the load-CMOD relationship is a more reliable parameter for determining the fracture characteristics because it is unaffected by the specimen setup and any support crushing. An important step towards the use of load-(:MOD concept as a key fracture parameter depends on relating the CMODto the traditional load-line deflection. This investigation found that there was an unique linear relationship between the CMOD and the load-line deflection. The exact numeric value of relationship between the CMOD and the deflection. that is, the slope ofthe line, is discovered to be a material property. The relationship finds a problem with the existing IZIL,EM recommendations for. measuring the fracture energy of concrete. A proposal to correct the problem is made.

• International Journal of Concrete Structures and Materials
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• v.11 no.2
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• pp.391-401
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• 2017

In this study, the effects of water-to-binder (W/B) ratio and replacement ratio of blast furnace slag (BFS) on the compressive strength of concrete were first investigated to determine an optimized mixture. Then, using the optimized high-strength concrete (HSC) mixture, hooked steel fibers with various aspect ratios and volume fractions were used as additives and the resulting mechanical properties under compression and flexure were evaluated. Test results indicated that replacement ratios of BFS from 50 to 60% were optimal in maximizing the compressive strength of steam-cured HSCs with various W/B ratios. The use of hooked steel fibers with the aspect ratio of 80 led to better mechanical performance under both compression and flexure than those with the aspect ratio of 65. By increasing the fiber aspect ratio from 65 to 80, the hooked steel fiber volume content could be reduced by 0.25% without any significant deterioration of energy absorption capacity. Lastly, complete material models of steel-fiber-reinforced HSCs were proposed for structural design from Lee's model and the RILEM TC 162-TDF recommendations.

• Structural Engineering and Mechanics
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• v.56 no.2
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• pp.275-291
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• 2015

Adherence between reinforcement and the surrounding concrete is usually ignored in finite element analysis (FEA) of reinforced concrete (RC) members. However, load transition between the reinforcement and surrounding concrete effects RC members' behavior a great deal. In this study, the effects of bond-slip on the FEA of RC members are examined. In the analyses, three types of bond-slip modeling methods (perfect bond, contact elements and spring elements) and three types of reinforcement modeling methods (smeared, one dimensional line and three dimensional solid elements) were used. Bond-slip behavior between the reinforcement and surrounding concrete was simulated with cohesive zone materials (CZM) for the first time. The bond-slip relationship was identified experimentally using a beam bending test as suggested by RILEM. The results obtained from FEA were compared with the results of four RC beams that were tested experimentally. Results showed that, in FE analyses, because of the perfect bond occurrence between the reinforcement and surrounding concrete, unrealistic strains occurred in the longitudinal reinforcement. This situation greatly affected the load deflection relationship because the longitudinal reinforcements dominated the failure mode. In addition to the spring elements, the combination of a bonded contact option with CZM also gave closer results to the experimental models. However, modeling of the bond-slip relationship with a contact element was quite difficult and time consuming. Therefore bond-slip modeling is more suitable with spring elements.

• Advances in concrete construction
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• v.1 no.1
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• pp.1-27
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• 2013

Discrete steel fibres can increase significantly the bending and the shear resistance of concrete structural elements when Steel Fibre Reinforced Concrete (SFRC) is designed in such a way that fibre reinforcing mechanisms are optimized. To assess the fibre reinforcement effectiveness in shallow structural elements failing in bending and in shear, experimental and numerical research were performed. Uniaxial compression and bending tests were executed to derive the constitutive laws of the developed SFRC. Using a cross-section layered model and the material constitutive laws, the deformational behaviour of structural elements failing in bending was predicted from the moment-curvature relationship of the representative cross sections. To evaluate the influence of the percentage of fibres on the shear resistance of shallow structures, three point bending tests with shallow beams were performed. The applicability of the formulation proposed by RILEM TC 162-TDF for the prediction of the shear resistance of SFRC elements was evaluated. Inverse analysis was adopted to determine indirectly the values of the fracture mode I parameters of the developed SFRC. With these values, and using a softening diagram for modelling the crack shear softening behaviour, the response of the SFRC beams failing in shear was predicted.