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REFERENCE LINKING PLATFORM OF KOREA S&T JOURNALS
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Journal of the Korea Concrete Institute
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Korea Concrete Institute
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Volume & Issues
Volume 21, Issue 6 - Dec 2009
Volume 21, Issue 5 - Oct 2009
Volume 21, Issue 4 - Aug 2009
Volume 21, Issue 3 - Jun 2009
Volume 21, Issue 2 - Apr 2009
Volume 21, Issue 1 - Feb 2009
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A Study on Chloride Threshold Level of Blended Cement Mortar Using Polarization Resistance Method
Song, Ha-Won ; Lee, Chang-Hong ; Lee, Kewn-Chu ; Ann, Ki-Yong ;
Journal of the Korea Concrete Institute, volume 21, issue 3, 2009, Pages 245~253
DOI : 10.4334/JKCI.2009.21.3.245
The importance of chloride ions in the corrosion of steel in concrete has led to the concept for chloride threshold level (CTL). The CTL can be defined as the content of chlorides at the steel depth that is necessary to sustain local passive film breakdown and hence initiate the corrosion process. Despite the importance of the CTL, due to the uncertainty determining the actual limits in various environments for chloride-induced corrosion, conservative values such as 0.4% by weight of cement or 1.2 kg in 1
concrete have been used in predicting the corrosion-free service life of reinforced concrete structures. The paper studies the CTL for blended cement concrete by comparing the resistance of cementitious binder to the onset of chloride-induced corrosion of steel. Mortar specimens were cast with centrally located steel rebar of 10 mm in diameter using cementitious mortars with ordinary Portland cement (OPC) and mixed mortars replaced with 30% pulverized fuel ash (PFA), 60% ground granulated blast furnace slag (GGBS) and 10% silica fume (SF), respectively, at 0.4 of a free W/B ratio. Chlorides were admixed in mixing water ranging 0.0, 0.2, 0.4, 0.6, 0.8, 1.0, 1.5, 2.0, 2.5 and 3.0% by weight of binder(Based on
). Specimens were curd 28 days at the room temperature, wrapped in polyethylene film to avoid leaching out of chloride and hydroxyl ions. Then the corrosion rate was measured using the polarization resistance method and the order of CTL for binder was determined. Thus, CTL of OPC, 60%GGBS, 30%PFA and 10%SF were determined by 1.6%, 0.45%, 0.8% and 2.15%, respectively.
Analytical Modeling for Microstructural Permeability Coefficient of (Non)Carbonated Concrete
Yoon, In-Seok ;
Journal of the Korea Concrete Institute, volume 21, issue 3, 2009, Pages 255~264
DOI : 10.4334/JKCI.2009.21.3.255
Permeability coefficient of concrete is a substaintial key parameter for understanding the durability performance of concrete and its microstructural densification. Many researches for the issue have been accomplished, however, it is very rare to deal with the theoretical study on permeability coefficient in connection with carbonation of concrete and the the effect of volumetric fraction of cement paste or aggregate on the permeability coefficient. The majority of these researches have not dealt with this issue combined with carbonation of concrete, although carbonation can significantly impact on the permeability coefficient of concrete. The purpose of this study is to establish a fundamental approach to compute the permeability coefficeint of (non)carbonated concrete. When simulating a microstructural characteristics as a starting point for deriving a model for the permeability coefficient by the numerical simulation program for cementitious materials, HYMOSTRUC, a more realistic formulation can be achieved. For several compositions of cement pastes, the permeability coefficient was calculated with the analytical formulation, followed by a microstructure-based model. Emphasis was on the microstructural changes and its effective change of the permeability coefficient of carbonated concrete. For carbonated concrete, reduced porosity was calculated and this was used for calculating the permeability coefficeint. The computational result was compared with experimental outcome.
An Experimental Study on the Creep Behavior and Crack Resistance of Hwang-toh Concrete Mixed with Recycled-PET Fiber
Kim, Sung-Bae ; Jay Kim, Jang-Ho ; Han, Byung-Goo ; Hong, Geon-Ho ; Song, Jin-Gyu ;
Journal of the Korea Concrete Institute, volume 21, issue 3, 2009, Pages 265~273
DOI : 10.4334/JKCI.2009.21.3.265
There have been numerous studies to develop eco-friendly concrete. The attempt to reduce the amount of cement used is suggested as one of the solutions for eco-friendly concrete. To decrease the usage of cement, the pozzolan reaction materials are used as a mineral admixture. Hwang-toh, which is broadly deposited in Korea is a well known environment friendly material and the activated hwang-toh, which has the property of pozzolan reaction, is alternatively used as a mineral admixture of concrete. The purpose of this study is to investigate the drying shrinkage of hwang-toh concrete mixed with recycled PET fiber. Therefore, drying shrinkage experiments are performed to analyze mechanical property of hwang-toh concrete mixed with recycled PET fiber. Test results showed that the drying shrinkage is controlled by hwang-toh admixture and PET fiber.
Bond Properties of CFRP Rebar in Fiber Reinforced High Strength Concrete with Surface Treatment Methods of Reinforcing Fibers
Park, Chan-Gi ; Won, Jong-Pil ; Cha, Sang-Sun ;
Journal of the Korea Concrete Institute, volume 21, issue 3, 2009, Pages 275~282
DOI : 10.4334/JKCI.2009.21.3.275
The effects of surface treatment method of reinforcing fiber on the bonding strength between carbon fiber reinforced polymer rebar (CFRP rebar) and high strength concrete have been evaluated in this study. The structural PVA fiber is coated with a proprietary hydrophobicoiling agent and crimped type polyolefin based structural synthetic fiber is deformed with a geometrical modification were used for the reinforcing fiber. The compressive tests have been performed to evaluate the strength property of high strength concrete depending on the surface treatment method of fiber. The bonding property between the high strength concrete and the CFRP rebar was evaluated by means of direct bonding test. The test results indicated that the surface treatment method of fiber effect on the bonding behavior of high strength concrete and CFRP rebar. Also, as the development and propagation of splitting cracks were controled by adding fibers into the high strength concrete, the bonding behavior, bond strength and relative bonding strength of CFRP rebar and high strength concrete were significantly improved.
Mix Design and Characteristics of Compressive Strengths for Foam Concrete Associated with the Application of Bottom Ash
Kim, Sang-Chel ; Ahn, Sang-Ku ;
Journal of the Korea Concrete Institute, volume 21, issue 3, 2009, Pages 283~290
DOI : 10.4334/JKCI.2009.21.3.283
Differently from fly ash, the bottom ash produced from thermoelectric power plant has been treated as an industrial waste matter, and almost reclaimed a tract from the sea. If this waste material is applicable to foam concrete as an aggregate owing to its light-weight, however, it may be worthy of environmental preservation by recycling of waste material as well as reducing self-weight of high-rising structure and horizontal forces and deformations of retaining wall subject to soil pressure. This study has an objective of evaluating the effects of application of bottom ash on the mechanical properties of foam concrete. Thus, the ratio of bottom ash to cement was selected as a variable for experiment and the effect was measured in terms of unit weight of concrete, air content, water-cement ratio and compressive strength. It can be observed from experiments that the application ratios have different effects on the material parameters considered in this experiment, thus major relationships between application ratio and each material parameter were finally introduced. The result of this study can be applied to decide a mix design proportion of foam concrete while bottom ash is used as an aggregate of the concrete.
Behavior and Capacity of Compression Lap Splice in Unconfined Concrete with Compressive Strength of 40 and 60 MPa
Chun, Sung-Chul ; Lee, Sung-Ho ; Oh, Bo-Hwan ;
Journal of the Korea Concrete Institute, volume 21, issue 3, 2009, Pages 291~302
DOI : 10.4334/JKCI.2009.21.3.291
A compression lap splice can be calculated longer than a tension lap splice in high strength concrete according to current design codes. New criteria for the compression lap splice including the effects of concrete strength are required for practical purpose of ultra-high strength concrete. Characteristics of compression lap splice have been extensively investigated and main parameters are derived. In addition, an experimental study has been conducted with column specimens in concrete strength of 40 and 60 MPa. The strength of the compression lap splice consists of bond and end bearing and two contributors are combined. Therefore, combined action of bond and end bearing should be assessed. Compared with tension splices, concrete strength significantly affects the strength of compression splices due to short splice length and existence of end bearing. Test results show that the splice strength can be evaluated to be proportional to square root of compressive strength of concrete. The stress states of concrete surrounding spliced bars govern the strengths of bond and end bearing. Because the axial stress of the concrete is relatively high, the splice strength is not dependent on clear spacing. End bearing strength is not affected by splice length and clear spacing and is expressed with a function of the square root of concrete strength. The failure mode of specimens is similar to side-face blowout of pullout test of anchors and the strength of end bearing can be evaluated using the equation of side-face blowout strength. Because the stresses developed by bond in compression splices are nearly identical to those in tension splices, strength increment of compression splices is attributed to end bearing only.
An Experimental Study on Transfer Length of Domestic CFRP Tendon
Jung, Woo-Tai ; Park, Young-Hwan ;
Journal of the Korea Concrete Institute, volume 21, issue 3, 2009, Pages 303~310
DOI : 10.4334/JKCI.2009.21.3.303
CFRP(carbon fiber reinforced polymer) tendons can be used as an alternative to solve the corrosion problem of steel tendons. Material properties of CFRP tendons such as bond strength, transfer length, and development length should be determined in order to apply to concrete structures. First of all, in case of application for pretension concrete members with CFRP tendons, transfer length is an important factor. A total of 9 beams have been cast to determine transfer length and development length of domestic CFRP tendon in this paper. Test results revealed that transfer length of the prestressing 25% and 50% are 34D, 55D respectively. Also, transfer length has increased as the prestressing force has increased. A change was observed in transfer length of developed CFRP tendon after 9 weeks.
of developed CFRP tendon was 2.3 similar to the steel strand.
The Volumetric Ratio of Transverse Reinforcement of R/C Columns Considering Effective Lateral Confining Reduction Factor
Kim, Jong-Keun ; Ahn, Jong-Mun ; Shin, Sung-Woo ;
Journal of the Korea Concrete Institute, volume 21, issue 3, 2009, Pages 311~318
DOI : 10.4334/JKCI.2009.21.3.311
An experimental investigation was conducted to examine the hysteretic behaviors of ultra-high strength concrete tied columns. The purpose of this study is to propose the volumetric ratio of transverse reinforcement for ultra-high strength concrete tied columns with 100 MPa compressive strength. Nineteen 1/3 scaled columns were fabricated to simulate an 1/2 story of actual structural members with the main variables of axial load ratio, configurations and volumetric ratios of transverse reinforcement. The results show that the deformability of columns are affected by the configurations and volumetric ratios of transverse reinforcement. Especially, it has been found that the behavior of columns are affected by axial load ratio rather than the amounts and the configurations of transverse reinforcement. To improve the ductility behavior of RC column using ultra high strength concrete in a seismic region, We suggested the amount of transverse reinforcement for all data that satisfy the required displacement ductility ratio over 4. It is means that the lateral confining reduction factor (
) considering the effective legs, configuration and spacing of transverse reinforcement and axial load ratio was reflected for the volumetric ratio of transverse reinforcement.
An Experimental Study on Punching Shear at the Connection of RC Column Constrained by H-Beam with 井 Shape
Kim, Lyang-Woon ; Lee, Soo-Kueon ; Lee, Jung-Yoon ; Chung, Chang-Yong ; Kim, Sang-Sik ;
Journal of the Korea Concrete Institute, volume 21, issue 3, 2009, Pages 319~326
DOI : 10.4334/JKCI.2009.21.3.319
Two parallel wide flange built-up beams are widely used as struts in resisting lateral earth pressure because of the effectiveness in structure and construction. In a certain structural system, the reinforced concrete columns are to be placed at the intersection where two perpendicular beams cross each other, the square part of the joint being filled with concrete. In the punching shear mechanism of the beam-column joint, the radial deformation caused due to shear cracking will be constrained by the spring action of the squarely encompassed beam flanges. As a result, the punching shear strength of the joint concrete can be expected to be increased. To verify this phenomenon experiments have been performed for various constraining elements and distances between columns and constraints. Test results are compared with the approximation analysis formula which has been proposed in this study, based on the code formula. The results calculated by the proposed equation show comparatively close agreement with the punching shear strength detected from the test.
Seismic Performance of Precast Infill Walls with Strain-Hardening Cementitious Composites
Kim, Sun-Woo ; Yun, Hyun-Do ; Jang, Gwang-Soo ; Yun, Yeo-Jin ;
Journal of the Korea Concrete Institute, volume 21, issue 3, 2009, Pages 327~335
DOI : 10.4334/JKCI.2009.21.3.327
In the seismic region, non-ductile structures often form soft story and exhibit brittle collapse. However, structure demolition and new structure construction strategies have serious problems, as construction waste, environmental pollution and popular complain. And these methods can be uneconomical. Therefore, to satisfy seismic performance, so many seismic retrofit methods have been investigated. There are some retrofit methods as infill walls, steel brace, continuous walls, buttress, wing walls, jacketing of column or beam. Among them, the infilled frames exhibit complex behavior as follows: flexible frames experiment large deflection and rotations at the joints, and infilled shear walls fail mainly in shear at relatively small displacements. Therefore, the combined action of the composite system differs significantly from that of the frame or wall alone. Purpose of research is evaluation on the seismic performance of infill walls, and improvement concept of this paper is use of SHCCs (strain-hardening cementitious composites) to absorb damage energy effectively. The experimental investigation consisted of cyclic loading tests on 1/3-scale models of infill walls. The experimental results, as expected, show that the multiple crack pattern, strength, and energy dissipation capacity are superior for SHCC infill wall due to bridging of fibers and stress redistribution in cement matrix.
An Experimental Study on the Shear Behavior of RC Beams Strengthened with Near Surface Mounted and Externally Bonded CFRP Strips
Lim, Dong-Hwan ; Kwon, Yeong-Soon ;
Journal of the Korea Concrete Institute, volume 21, issue 3, 2009, Pages 337~345
DOI : 10.4334/JKCI.2009.21.3.337
The purpose of this study is to investigate the shear strengthening effectiveness of the beams strengthened with near surface mounted (NSM) and external bonded (EB) CFRP strips. A total of nine concrete beams were made and tested. From this study, it was found that the shear stiffness and strength of the beams strengthened with NSM and EB strips were significantly improved compared to the control beam. Failure of the beam strengthened with NSM and EB strips was initiated by shear cracks, propagated diagonally to the adjacent epoxy grooves without crossing the epoxy and finally sudden diagonal crack connecting the point of application of load and flexural crack was occurred. For the beam strengthened combined with NSM and EB CFRP strips, the tensile strains in the NSM CFRP strips were observed in the range of 0.35% to 0.45% and strains with EB strips were measured about 0.3%.
Applicability of Partial Post-Tension Method for Deflection Control of Reinforced Concrete Slabs
Lee, Deuck-Hang ; Kim, Kang-Su ; Kim, Sang-Sik ; Kim, Yong-Nam ; Lim, Joo-Hyuk ;
Journal of the Korea Concrete Institute, volume 21, issue 3, 2009, Pages 347~358
DOI : 10.4334/JKCI.2009.21.3.347
Recently, it is getting into a good situation for the flat-plate slab system to be applied. The flat-plate slab without beam, however, is often too weak to control deflection properly compared to other typical slab-beam structures, for which the post-tension method is generally regarded as one of best solutions. The post-tension (PT) method can effectively control deflection without increase of slab thickness. Despite this good advantage, however, the application of PT method has been very limited due to cost increase, technical problems, and lack of experiences. Therefore, in order to reduce difficulties on applying full PT method under the current domestic circumstances and to enhance constructability of PT system, this research proposed the partial PT method with top jacking anchorage applied in a part of span as need. For the top jacking anchorage system, the efficiency of deflection control shall be considered in detail because it can vary widely depending on the location of anchorage that can be placed anywhere as need, and tensile stresses induced at back of the anchorage zone also shall be examined. Therefore, in this study, analysis were performed on the efficiency of deflection control depending on the location of anchorage and on tensile stresses or forces using finite element method and strut and tie model in the proposed top jacking anchorage system. The proposed jacking system were also applied to the floor slabs at a construction site to investigate its applicability and the analysis results of slab behavior were compared to the measured values obtained from the PT slab constructed by the partial PT method. The result of this study indicates that the partial PT method can be very efficiently applied with little cost increase to control deflection and tensile stresses in the region as a need basis where problem exists.
Development of a Successive LCC Model for Marine RC Structures Exposed to Chloride Attack on the Basis of Bayesian Approach
Jung, Hyun-Jun ; Park, Heung-Min ; Kong, Jung-Sik ; Zi, Goang-Seup ; Kim, Gyu-Seon ;
Journal of the Korea Concrete Institute, volume 21, issue 3, 2009, Pages 359~366
DOI : 10.4334/JKCI.2009.21.3.359
A new life-cycle cost (LCC) evaluation scheme for marine reinforced concrete structures is proposed. In this method, unlike the conventional life-cycle cost evaluation performed during the design process, the life-cycle cost is updated successively whenever new information of the chloride penetration is available. This updating is performed based on the Bayesian approach. For important structures, information required for this new method can be obtained without any difficulties because it is a common element of various types of monitoring systems. Using the new method, the life-cycle maintenance cost of structures can be estimated with a good precision.
Appraisal of Concrete Performance and Plan for Stable Use of EAF Oxidizing Slag as Fine Aggregate of Concrete
Cho, Bong-Suk ; Lee, Hoon-Ha ; Yang, Seung-Kyu ; Lee, Woong-Jong ; Um, Tai-Sun ;
Journal of the Korea Concrete Institute, volume 21, issue 3, 2009, Pages 367~375
DOI : 10.4334/JKCI.2009.21.3.367
Recently, more focus is shift to imbalances in aggregate market supply and demand and an exhaustion of natural resources. In this situation, Electric arc furnace oxidizing slag (EAF slag) has high application possibility as aggregate for concrete due to similar property with general aggregate. However, it is inherent the problem which causes pop-out by free-CaO contained in slag In this study, we`ve got the plan to assure the chemical stability of EAF slag, and then experimentally tested the mechanical performance and durability for the fine aggregate used EAF slag. On this test result, we suggest the application plan. At the result of this study, it shows that EAF slag would reduce the surface defect such as pop-out due to natural aging for the fixed hour and adjustment the grain size of EAF slag. And mechanical performance and durability according to the replacement rate of concrete service, were revealed more than equal or equal compare to general aggregate. Hereafter, quality control must precede not to impede the beauty of concrete surface as assure the safety for aging and processing. And, to establish the environmental resource recycling system for by-products of steel, it should be made development of various application and guideline of quality control for the EAF slag aggregate. Moreover, it must be constantly studied all kind of engineering performance and durability for related to this study.
Chloride Diffusion Coefficient Model Considering the Initiation Time of Exposure to Chloride Environment
Kim, Ki-Hyun ; Cha, Soo-Won ;
Journal of the Korea Concrete Institute, volume 21, issue 3, 2009, Pages 377~386
DOI : 10.4334/JKCI.2009.21.3.377
A reference diffusion coefficient model from ACI life-365 is drawn from test results by NT build 443. This test method gives a time-averaged diffusion coefficient during immersion period, thus the ACI model uses the time-averaged diffusion coefficient as a reference value. ACI model needs to be revised, considering the difference between the time-average value and reference value at specified time. In this study, firstly the analytic solutions of diffusion equation are derived considering the initiation time and period of exposure to chloride, and secondly the time-averaged diffusion coefficient from NT build 443 is converted into the diffusion coefficient at reference time. From this study, the reference diffusion coefficient of ACI model should be modified to be about 10% larger values than those of present ACI model. For convenient design of service life, previous relationship between the chloride diffusion coefficient from NT build 443 and that from NT build 492 is also modified. To compare the chloride diffusion coefficients of ACI and JCI models, the reference chloride diffusion coefficient with respect to the JCI model is drawn in the similar form of ACI model`s, and service life prediction by ACI life-365 method is confirmed to give a conservative result.