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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 24, Issue 6 - Dec 2012
Volume 24, Issue 5 - Oct 2012
Volume 24, Issue 4 - Aug 2012
Volume 24, Issue 3 - Jun 2012
Volume 24, Issue 2 - Apr 2012
Volume 24, Issue 1 - Feb 2012
Selecting the target year
Micro-Cracks Control of LB-DECK Using Polymer Cement Concrete
Lho, Byeong-Cheol ; Choi, Jong-Yun ; Cho, Gyu-Dae ; Choi, Jong-Gwon ;
Journal of the Korea Concrete Institute, volume 24, issue 2, 2012, Pages 103~109
DOI : 10.4334/JKCI.2012.24.2.103
Micro-cracks with a width less than 0.1 mm in precast concrete panels do not cause structural problem, but they can cause problems in long term durability and concrete surfaces aesthetic, requiring additional repair costs. In this paper, polymer cement concrete is used to increase flexural tensile strength and to prevent micro-cracks due to construction loads on LB-DECK panels. Using 5% polymer-cement ratio, the panel crack moment is increased by improving flexural tensile strength and controlling visible micro-cracks during construction stage of LB-DECK.
Effects of Fiber Blending Condition and Expansive Admixture Replacement on Tensile Performance of Rebar Lap Splice in Strain-Hardening Cement-Based Composites (SHCCs)
Ryu, Seung-Hyun ; Lee, Young-Oh ; Yun, Hyun-Do ;
Journal of the Korea Concrete Institute, volume 24, issue 2, 2012, Pages 111~120
DOI : 10.4334/JKCI.2012.24.2.111
This paper is a report about lap splice performance of rebar embedded in the strain-hardening cement-based composites (SHCCs) under monotonic and repeated tension loading. Ten mix proportions of cement-based composites such as SHCCs and normal concrete were investigated. The study parameters are comprised of (1) types of reinforcing fibers (polyethylene and steel fiber), (2) replacement levels of expansive admixture (EXA, 0% and 10%), and (3) compressive strength (30 and 100 MPa) of cement-based composites. Lap splice lengths (ld) of rebars in SHCC materials and normal concrete were 60% and 100% of splice length calculated by code requirements for structural concrete, respectively. Test results indicated that SHCCs materials can lead to enhancements in the lap splice performance of embedded rebar. All of the fiber reinforcement conditions (PE-SHCC and PESF-SHCC) considered in this study produced considerable improvements in the tensile strength, cracking behavior, and bond strength of lap-spliced rebar. Furthermore, adding EXA to SHCC matrix improved the tensile lap splice performance of rebar in SHCC materials. However, for controlling crack behavior, the performance of PE-SHCC was better than that of PESF-SHCC due to its mechanical properties. This study demonstrated an effective approach for reducing required development length of lap spliced rebar by using SHCC materials.
Basic Mixing and Mechanical Tests on High Ductile Fiber Reinforced Cementless Composites
Cho, Chang-Geun ; Lim, Hyun-Jin ; Yang, Keun-Hyeok ; Song, Jin-Kyu ; Lee, Bang-Yeon ;
Journal of the Korea Concrete Institute, volume 24, issue 2, 2012, Pages 121~127
DOI : 10.4334/JKCI.2012.24.2.121
Cement has been traditionally used as a main binding material of high ductile fiber reinforced cementitious composites. The purpose of this paper is to investigate the feasibility of using alkali-activated slag and polyvinyl alcohol (PVA) fibers for manufacturing high ductile fiber reinforced cementless composites. Two mixture proportions with proper flowability and mortar viscosity for easy fiber mixing and uniform fiber dispersion were selected based on alkali activators. Then, the slump flow, compression, uniaxial tension and bending tests were performed on the mixes to evaluate the basic properties of the composites. The cementless composites showed an average slump flow of 465 mm and tensile strain capacity of approximately 2% of due to formation of multiple micro-cracks. Test results demonstrated a feasibility of manufacturing high ductile fiber reinforced composites without using cement.
Experimental Evaluation of Bearing and Bond Strengths in Compression Splices
Chun, Sung-Chul ; Lee, Sung-Ho ;
Journal of the Korea Concrete Institute, volume 24, issue 2, 2012, Pages 129~136
DOI : 10.4334/JKCI.2012.24.2.129
Compression splices are required for all compression members in almost all of the floors in high-rise buildings. Therefore, a clear understanding of the behavior of compression splices can provide a rational design of compression splices. Tests of compression splices with bearing only and bond only cases were conducted to investigate the component resistance characteristics of compression splices. Test results showed that the circumferential tensile stresses induced by bearing and bond overlapped at the end of the splice length deterred bond and bearing splices from developing target splicing strength when both normal bond and bearing splices were used. In particular, the bearing strength was more significantly reduced than the bond strength since the bearing relied on the limited area near the end of the splice length. However, the strength of the normal splice was always higher than the strength of the bond only or the bearing only case. Consequently, the study results showed that splice strength in compression cannot be improved by means of removing bond or bearing. In addition, the bond strength in bond only splices was nearly same as the bond strength in tension splices and the strength increase of compression splice is attributed to end bearing only characteristic.
Strength Development of Blended Sodium Alkali-Activated Ground Granulated Blast-Furnace Slag (GGBS) Mortar
Kim, Geon-Woo ; Kim, Byeong-Jo ; Yang, Keun-Hyeok ; Song, Jin-Kyu ;
Journal of the Korea Concrete Institute, volume 24, issue 2, 2012, Pages 137~145
DOI : 10.4334/JKCI.2012.24.2.137
Strength model for blasted furnace slag mortar blended with sodium was investigated in this study. The main parameters of AAS (alkali activated slag) mortar were dosage of alkali activator, water to binder ratio (W/B), and aggregate to binder ratio (A/B). For evaluating the property related to the dosage of alkali activator, sodium carbonate (
) of 4~8% was added to 4% dosage of sodium hydroxide (NaOH). W/B and A/B was varied 0.45~0.60 and 2.05~2.85, respectively. An alkali quality coefficient combining the amounts of main compositions of source materials and sodium oxide (
) in sodium hydroxide and sodium carbonate is proposed to assess the compressive strength of alkali activated mortars. Test results clearly showed that the compressive strength development of alkali-activated mortars were significantly dependent on the proposed alkali quality coefficient. Compressive strength development of AAS mortars were also estimated using the formula specified in the previous study, which was calibrated using the collected database. Predictions from the simplified equations showed good agreements with the test results.
Behavior of Reinforced Concrete Inclined Column-Beam Joints
Kwon, Goo-Jung ; Park, Jong-Wook ; Yoon, Seok-Gwang ; Kim, Tae-Jin ; Lee, Jung-Yoon ;
Journal of the Korea Concrete Institute, volume 24, issue 2, 2012, Pages 147~156
DOI : 10.4334/JKCI.2012.24.2.147
In recent years, many high-rise buildings have been constructed in irregular structural system with inclined columns, which may have effect on the structural behavior of beam-column joints. Since the external load leads to shear and flexural forces on the inclined columns in different way from those on the conventional vertical columns, failure mode, resistant strength, and ductility capacity of the inclined column-beam joints may be different than those of the perpendicular beam-column joints. In this study, six RC inclined beam-column joint specimens were tested. The main parameter of the specimens was the angle between axes of the column and beam (90, 67.5, and 45 degree). Test results indicated that the structural behavior of conventional perpendicular beam-column joint was different to that of the inclined beam-column joints, due to different loading conditions between inclined and perpendicular beam-column joints. Both upper and lower columns of perpendicular beam-column joints were subjected to compressive force, while the upper and lower columns of the inclined beam-column joints were subjected to tensile and compressive forces, respectively.
Shear Behavior of Reinforced Concrete Beams according to Replacement Ratio of Recycled Coarse Aggregate
Kim, Sang-Woo ; Jeong, Chan-Yu ; Jung, Chang-Kyo ; Kim, Kil-Hee ;
Journal of the Korea Concrete Institute, volume 24, issue 2, 2012, Pages 157~164
DOI : 10.4334/JKCI.2012.24.2.157
This study evaluates the shear performance of reinforced concrete beams with recycled coarse aggregates. A total of six specimens with various replacement ratios of recycled coarse aggregates (0%, 50%, and 100%) and different amount of shear reinforcement were cast and tested in this study. A finite element analysis was performed to predict the shear behavior of the specimens with natural or recycled coarse aggregates. The FE analysis was performed using a two-dimensional nonlinear FE analysis program based on the disturbed stress field model (DSFM), which is an extension of the modified compression field theory (MCFT). Experimental results showed that the specimens with 50% and 100% replacement ratios of recycled coarse aggregates had the similar shear strength compared to the specimen with natural aggregates, regardless of the replacement ratios of recycled coarse aggregates and the amount of the shear reinforcement. Furthermore, the comparison between experimental and analytical results showed that the proposed numerical modeling methods and the analytical model, DSFM, can be successfully used to predict the shear behavior of reinforced concrete beams with recycled coarse aggregates.
Experimental Study on Engineering Performance Evaluation and Field Performance of Environmentally Friendly Functional Concrete
Lee, Byung-Jae ; Park, Seong-Bum ; Kim, Yun-Yong ; Jang, Young-Il ;
Journal of the Korea Concrete Institute, volume 24, issue 2, 2012, Pages 165~172
DOI : 10.4334/JKCI.2012.24.2.165
In this study, the physical, mechanical, structural, and environmental performances based on field measured data were evaluated to check the suitability of concrete for ecological preservation and cultivation of a hydrophilic environment. More specifically, the study is focused on developing an environmentally friendly functional concrete with river ecology restoration and natural river early formation capabilities. The mechanical performance evaluation results showed that the increase in mix rate of the PVA (Poly Vinyl Alcohol) reinforcement fibers and silica fume caused an increase in the strength. The optimal mix rate was found to be 0.05 volume % PVA fiber and approximately 10% silica fume. The frost resistance evaluation showed that superior performance was gained when 0.05 volume % PVA fiber and 15% silica fume was mixed simultaneously. In the structural performance evaluation, the bending strength was improved by 47.7% compared to plain concrete when mixed with 0.05 volume % PVA fiber. The flexural toughness also saw significant improvement. The environmental monitoring of field performance showed that grasses germinated most rapidly, but the growth of red poppies, a plant that germinates in the spring, was most active with passing of time. Coverage measurements in all of the monitoring locations found favorable coverage of over 95% after 12 weeks. The study results showed that the environmentally friendly functional concrete had outstanding environmental performance.
Evaluation on Spalling Properties of Ultra High Strength Concrete with Melting and Vaporization of Fiber
Kim, Gyu-Yong ; Choe, Gyeong-Cheol ; Lee, Joo-Ha ; Lee, Seung-Hoon ; Lee, Tae-Gyu ;
Journal of the Korea Concrete Institute, volume 24, issue 2, 2012, Pages 173~183
DOI : 10.4334/JKCI.2012.24.2.173
Recently, experimental studies to prevent explosive spalling based on spalling mechanism and addition of Polypropylene fiber in high strength concrete (HSC) are performed actively. However, with respect to ultra high strength concrete (UHSC), its compact internal structure is more difficult release vapor pressure at rapid rising temperature compared to HSC. Therefore, in this study, an experiment was conducted to evaluate spalling properties of UHSC using
rectangular specimen according to ISO-834 standard fire curve. With respect melting point of fiber, three fiber types of Polyethylene, Polypropylene, and Nylon fibers with melting temperature of
, respectively, were considered. Mixed fiber of 0.15% and 0.25% of concrete volume was used to consider spalling properties based on water vapor pressure release. Then, TGDTA test on fiber and FEM analysis were performed. The results showed that it is difficult to prevent initial spalling without loss of fiber mass even if fiber melting temperature is low. Also, in preventing thermal spalling, fiber that melts to rapidly create porosity within 10 minutes of fire is more effective than that of low melting temperature property of fiber.
Estimation of Shear Strength of Beam-Column Joints
Choi, Ha-Young ; Kim, Byoung-Il ; Lee, Jung-Yoon ;
Journal of the Korea Concrete Institute, volume 24, issue 2, 2012, Pages 185~193
DOI : 10.4334/JKCI.2012.24.2.185
In this study, an estimation equation was proposed to predict the shear strength of RC interior beam-column connections. The proposed equation considered the effect of both truss and arch mechanisms, while the existing equations in the ACI and AIJ design codes consider only arch mechanism. In addition, the proposed equation estimates the shear strength of RC joints by considering the contribution of the vertical and horizontal steel bars on the effective compressive strength of concrete. The shear strength of RC joints calculated by the proposed equation was compared with the test results of 54 RC joints, which failed in shear before plastic hinges developed at the end of the adjacent beams. The comparison study showed that the proposed equation estimated the strength of the 54 specimens with a mean value of 1.14 and the coefficient of variation of 20%. The proposed equation provides improved prediction compared to those obtained from the equations in the ACI and AIJ design codes.
Mechanical Properties and Stress-Strain Model of Re-Bars Coldly Bent and Straightened
Chun, Sung-Chul ; Tak, So-Young ; Ha, Tae-Hun ;
Journal of the Korea Concrete Institute, volume 24, issue 2, 2012, Pages 195~204
DOI : 10.4334/JKCI.2012.24.2.195
In the construction of high-rise buildings, bent re-bars are manually straightened to connect slabs to core-walls, which are usually cast before floor structures. During cold bending and straightening of re-bars, plastic deformation causing work hardening, Bauschinger effect and aging hardening is unavoidable. Tensile tests of coldly bent and straightened re-bars were conducted with test parameters of grade, diameter, and bend radius of re-bars as well as age between bending and straightening. Test results showed that proportional limits were lower and strain hardening occurred without yield plateaus. Inside and outside of re-bars with compression and tension deformations, respectively, during bending showed lower yield points due to Bauschinger effect and no yield plateaus due to work hardening, respectively. When re-bar grade was higher, yield point became significantly lower where Grade 400 re-bars had yield strengths lower than specified yield strength of 400 MPa. Because the surface of re-bar has higher strength than the core of re-bar, Bauschinger effect was more obvious for higher-grade re-bars. When age between bending and straightening was greater, yield strength increased and elongation decreased (i.e. embrittlement occurs). Using measured data, stress-strain relationship for straightened re-bars was developed based on Ramberg-Osgood model, which can be used to evaluate stiffness of joints when straightened re-bars are applied.
Technique for the Measurement of Crack Widths at Notched / Unnotched Regions and Local Strains
Choi, Sok-Hwan ; Lim, Bub-Mook ; Oh, Chang-Kook ; Joh, Chang-Bin ;
Journal of the Korea Concrete Institute, volume 24, issue 2, 2012, Pages 205~214
DOI : 10.4334/JKCI.2012.24.2.205
Crack widths play an important role in the serviceability limit state. When crack widths are controlled sufficiently, the reinforcement corrosion can be reduced using only existing concrete cover thickness due to low permeability in the region of finely distributed hair-cracks. Thus, the knowledge about the tensile crack opening is essential in designing more durable concrete structures. Therefore, numerous researches related to the topic have been performed. Nevertheless accurate measurement of a crack width is not a simple task due to several reasons such as unknown potential crack formation location and crack opening damaging strain gages. In order to overcome these difficulties and measure precise crack widths, a displacement measurement system was developed using digital image correlation. Accuracy calibration tests gave an average measurement error of 0.069 pixels and a standard deviation of 0.050 pixels. Direct tensile test was performed using ultra high performance concrete specimens. Crack widths at both notched and unnotched locations were measured and compared with clip-in gages at various loading steps to obtain crack opening profile. Tensile deformation characteristics of concrete were well visualized using displacement vectors and full-field displacement contour maps. The proposed technique made it possible to measure crack widths at arbitrary locations, which is difficult with conventional gages such as clip-in gages or displacement transducers.