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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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Journal DOI :
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
Selecting the target year
Critical Strengthening Ratio of CFRP Plate Using Probability and Reliability Analysis for Concrete Railroad Bridge Strengthened by NSM
Oh, Hong-Seob ; Sun, Jong-Wan ; Oh, Kwang-Chin ; Sim, Jong-Sung ; Ju, Min-Kwan ;
Journal of the Korea Concrete Institute, volume 21, issue 6, 2009, Pages 681~688
DOI : 10.4334/JKCI.2009.21.6.681
The railroad bridges have been usually experienced by vibration and impact in service state. With this reason, it is important that the effective strengthening capacity should be considered to resist the kind of service loading. In this study, NSM strengthening technique is recommended for the concrete railroad bridge because of its better effective resistance for dynamic loading condition and strengthening cost than the conventional externally bonded strengthening using fiber sheet. However, to widely apply NSM method for the concrete railroad bridge, it needs that the strengthening ratio has to be reasonably evaluated with geometrical and material uncertainties, especially for the concrete bridge under long-term service state without the apparent design history and detail information such as concrete compressive strength, reinforcing ratio, railroad characteristics. The purpose of this study is to propose the critical strengthening ratio of CFRP plate for the targeted concrete railroad bridge with uncertainties of deterioration of the structures. To do this, Monte Carlo Simulation (MCS) for geometrical and material uncertainties have been applied so that this approach may bring the reasonable strengthening ratio of CFRP plate considering probabilistic uncertainties for the targeted concrete railroad bridge. Finally, the critical strengthening ratio of NSM strengthened by CFRP plate is calculated by using the limit state function based on the target reliability index of 3.5.
Corrosion Resistance of Blended Concrete and Its Application to Crack Healing
Lee, Chang-Hong ; Kim, Tae-Sang ; Song, Ha-Won ;
Journal of the Korea Concrete Institute, volume 21, issue 6, 2009, Pages 689~696
DOI : 10.4334/JKCI.2009.21.6.689
In this study, electro-deposition method was applied to heal cracks in various blended concrete. The performance of the method was indirectly monitored by measuring impressed voltage, electrolyte, galvanic current monitoring, linear polarization resistance, and directly by image analysis of the cracks. The indirect and direct monitoring values are compared to develop guidelines for relating the indirect measures to actual crack healing. As a result, It was found that impressed voltage was convergence to 2.9V after 20000 minutes. From the galvanic current test results of artificial crack healing, the corrosion resistance showed that the order of 0.4
0.5 water to cement ratio. Furthermore, in view of binder, the corrosion resistance order was calculated OPC
30%PFA. Finally, It was found that 76.47% of healed crack surface calculated from the artificial crack healing technique using electrochemical deposition method.
Enhancing the Performance of High-Strength Concrete Corbels Using Steel Fibers and Headed Bars
Yang, Jun-Mo ; Lee, Joo-Ha ; Shin, Hyun-Oh ; Yoon, Young-Soo ;
Journal of the Korea Concrete Institute, volume 21, issue 6, 2009, Pages 697~703
DOI : 10.4334/JKCI.2009.21.6.697
High-strength concrete corbels with varying percentage of steel fibers and two different anchorage types (welding to transverse bar, headed) for the main tension tie were constructed and tested. The results showed that performance in terms of load carrying capacities, stiffness, ductility, and crack width was improved, as the percentage of steel fibers was increased. In addition, the corbel specimens in which headed bars were used as the main tension tie reinforcements showed superior load carrying capacities, stiffness, and ductility compared to the corbel specimens in which the main tension ties were anchored by welding to the transverse bars. From the test results, it is expected that load carrying capacities, durability, and constructibility of high strength concrete corbels would be improved by using steel fibers and headed bars. Experimental results presented in this paper were also compared with various prediction models proposed by researchers and presented in codes. The truss model proposed by Fattuhi provides fairly good predictions for fiber reinforced high-strength concrete corbels.
Flexural and Impact Resisting Performance of HPFRCCs Using Hybrid PVA Fibers
Kim, Young-Woo ; Min, Kyung-Hwan ; Yang, Jun-Mo ; Yoon, Young-Soo ;
Journal of the Korea Concrete Institute, volume 21, issue 6, 2009, Pages 705~712
DOI : 10.4334/JKCI.2009.21.6.705
HPFRCCs (high-performance fiber reinforced cementitious composites), which is relatively more ductile and has the characteristic of high toughness with high fiber volume fractions, can be used in structures subjected to extreme loads and exposed to durability problems. In the case of PVA (polyvinyl alcohol) fiber, it is noted by former studies that around 2% fiber volume fractions contributes to the most effective performance at HPFRCCs. In this study, flexural tests were carried out to evaluate the flexural behavior of HPFRCCs and to optimize mix proportions. Two sets of hybrid fiber reinforced high performance specimens with total fiber volume fraction of 2 % were tested: the first set prepared by addition of short and long PVA fibers at different combination of fiber volume fractions, and the second set by addition of steel. In addition, in order to assess the performances of the HPFRCCs against to high strain rates, drop weight tests were conducted. Lastly, the sprayed FRP was applied on the bottom surface of specimens to compare their impact responses with non-reinforcing specimens. The experimental results showed that the specimen prepared with 1.6% short fibers (REC 15) and 0.4% long fiber (RF4000) outperformed the other specimens under flexure, and impact loading.
A Fundamental Study on Nano-cement by Chemical Synthesis
Jo, Byung-Wan ; Kang, Seok-Won ; Yoon, Kwang-Won ; Choi, Ji-Sun ;
Journal of the Korea Concrete Institute, volume 21, issue 6, 2009, Pages 713~718
DOI : 10.4334/JKCI.2009.21.6.713
Advanced industries-IT, BT, NT and ET are rapidly developing in 21 century. And the cement industry is becoming the principal factor in air pollution because of the creation of
during manufacturing. Also, the cement industry will be faced with a crisis due to the exhaustion of natural resources. In this study, nano cement by Bottom-up method of a chemical synthesis was developed. The generation of
during the plasticization process of cement manufacturing was avoided. The purpose was to produce building materials that have both high strength and durability as the high value-added growth engine industry of the 21 century. The nano cement was developed using hydrothermal synthesis. This is a method of mixing after ripening, by manufacturing the high density gel and low gel, which does not require special test equipment or pressure conditions to produce. Particle size, SEM, EDX, and porosity tests were conducted. This study investigated the compressive strength of concrete with various compositions. Specimens were tested for compressive strength at 3, 7, 14 and 28 days. The medium-sized (50% by weight) cement particles created by chemical synthesis were less than 168 nm. The compressive strength of the mortar prepared using this cement was 53.9 MPa. But it was judged that succeeding study will be necessary for development of nano building materials with high ability and economical analysis.
Evaluations of the Maximum Shear Reinforcement of Reinforced Concrete Beams
Hwang, Hyun-Bok ; Moon, Cho-Hwa ; Lee, Jung-Yoon ;
Journal of the Korea Concrete Institute, volume 21, issue 6, 2009, Pages 719~727
DOI : 10.4334/JKCI.2009.21.6.719
The requirements of the maximum shear reinforcement in the EC2-02 and CSA-04, which are developed based on the truss model, are quite different to those in the ACI-08 code and AIJ-99 code, which are empirical equations. The ACI 318-08, CSA-04, and EC2-02 codes provide an expression for the maximum amount of shear reinforcement ratio as a function of the concrete compressive strength, but Japanese code does not take the influence of the concrete compressive strength into account. For high strength concrete, the maximum amount of shear reinforcement calculated by the EC2-02 and CSA-04 is much greater than that calculated by the ACI 318-08. Ten RC beams having various shear reinforcement ratios were tested and their corresponding shear stress-shear strain curves and failure modes were compared to the predicted ones obtained by the current design codes.
Experimental Study on the Material Characteristics of Slag Cement with Various Phosphogypsum Materials
Park, Jong-Tak ; Oh, Hong-Seob ;
Journal of the Korea Concrete Institute, volume 21, issue 6, 2009, Pages 729~735
DOI : 10.4334/JKCI.2009.21.6.729
In this study, it is experimentally verified a feasibility of the wasted phosphogypsum (
) that is a byproduct from the phosphoric acid process of manufacturing fertilizers can be applied as an admixture in slag cement. For the test, phosphogypsum is modified as dihydrate, hemihydrate, type III anhydrite, and type II anhydrite, and then chemical characteristics and mechanical properties of various slag cements containing above mentioned gypsum materials were analyzed. The test results show that the gypsum made at high temperature has better quality with decrease of water-soluble phosphoric acid (
) which has an effect on the quality of cement. And type II anhydrite shows superior quality in terms of drying shrinkage and the compressive strength of cement paste with hemihydrate at 56 days is higher than other gypsum material.
An Experimental Study on Flexural Behavior of Steel Fiber Reinforced Ultra High Performance Concrete
Yang, In-Hwan ; Joh, Chang-Bin ; Kang, Su-Tae ; Kim, Byung-Suk ;
Journal of the Korea Concrete Institute, volume 21, issue 6, 2009, Pages 737~744
DOI : 10.4334/JKCI.2009.21.6.737
In this study, the flexural behavior of steel fiber reinforced ultra high performance concrete (UHPC) was investigated. It presents experimental results of steel fiber reinforced UHPC with steel fiber content of 2% by volume and steel reinforcement ratio of less than 0.02. This study aims at providing more information about UHPC beams in bending in order to establish a reasonable prediction model for flexural resistance and deflection in structural code in the future. The experimental results show that UHPC is in favor of cracking behavior and ductility of beams, and that the ductility indices range from 6.29 to 10.44, which means high ductility of UHPC. Also, the flexural rigidity of beam whose cast is begun from end of beam is larger than that of beam whose cast is begun from midspan of beam. This result represents that the flexural rigidity is affected by the placing method of UHPC.
Optimized Mixing Design of Lightweight Aerated Concrete by Response Surface Analysis
Lee, Sang-An ; Jung, Chan-Woo ; Kim, Wha-Jung ; Ahn, Jung-Hyun ;
Journal of the Korea Concrete Institute, volume 21, issue 6, 2009, Pages 745~752
DOI : 10.4334/JKCI.2009.21.6.745
This paper presents the optimized mixing design of lightweight aerated concrete using hydrogen peroxide. Design of experiments in order to the optimized mixing design was applied and commercial program (MINITAB) was used. Statistical analysis was used to Box-Behnken (B-B) method in response surface analysis. The influencing factors of experimental are unit cement content, water ratio and hydrogen peroxide ratio. According to the analysis of variance, at the hardened state, water ratio and hydrogen peroxide ratio affects on dried density, compressive strength and bending strength of lightweight aerated concrete, but unit cement content affects on only dried density. In the results of response surface analysis, to obtain goal performance, the optimized mixing design for lightweight aerated concrete using hydrogen peroxide were unit cement content of 800 kg/
, water ratio of 44.33% and hydrogen peroxide ratio of 10%.
Tension Lap Splice Length in High-Strength Concrete Flexural Members
Lee, Gi-Yeol ; Kim, Woo ; Lee, Hwa-Min ;
Journal of the Korea Concrete Institute, volume 21, issue 6, 2009, Pages 753~761
DOI : 10.4334/JKCI.2009.21.6.753
This paper presents the test results of total 24 beam-end specimens to investigate the effect of high-strength concrete and cover thickness on the development resistance capacity in tensile lap splice length regions. Based on bond characteristics that an increase in concrete strength results in higher bond stress and shortening of the transfer length, cracking behavior that thin cover thickness induced a splitting crack easily and brittle crack propagation, current design code that development length provisions as uniform bond stress assumption was investigated apply as it. The results showed that as higher strength concrete was employed, not only development resistance capacity was influenced by cover thickness, but also more sufficient safety factor reserved shorter than the lap splice length provision in current design code. From experimental research results, high-strength concrete development length was not inverse ratio of
but directly inverse of
, and it is also said that there is a certain limit length of the embedded steel over which the assumption of uniform bond stress distribution is valid specially for high-strength concrete not having a same embed length such as normal-strength concrete in current design criteria hypothesis.
Prediction Model of Unbonded Tendon Stresses in Post-Tensioned Members
Kim, Kang-Su ; Lee, Deuck-Hang ; Kal, Gyung-Wan ;
Journal of the Korea Concrete Institute, volume 21, issue 6, 2009, Pages 763~771
DOI : 10.4334/JKCI.2009.21.6.763
As the demand on long span structures increases more in recent years, the excessive deflection, in addition to the ultimate strength, in horizontal members becomes a very important issue. For this reason, as an alternative method to effectively solve the deflection problems, the application of post-tensioned structural system with unbonded tendon increases gradually. However, most of the existing researches on post-tensioned members with unbonded tendons (UPT) focused on the ultimate flexural strength, which would be impossible or improper to check serviceability such as deflections. Therefore, this study aims at proposing a stress prediction model for unbonded tendons that is applicable to the behavior of UPT members from the very initial loading stages, post-cracking states, and service to ultimate conditions. The applicability and accuracy of the proposed model were also evaluated comparing to the existing test results from literature. Based on such comparison results, it was verified that the proposed model provided very good predictions on tendon stresses of UPT members at various loading stages regardless their different characteristics; wide range of reinforcement index, different loading patterns, and etc. The proposed model especially well considered the effect of various loading types on stress increases of unbonded tendons, and it was also very suitable to apply on the over-reinforced members that easily happened during strengthening/repairing work.
Determination of Steel-Concrete Interface Parameters : Bonded and Unbonded Slip Tests
Lee, Ta ; Joo, Young-Tae ; Lee, Yong-Hak ;
Journal of the Korea Concrete Institute, volume 21, issue 6, 2009, Pages 773~780
DOI : 10.4334/JKCI.2009.21.6.773
Experiments on steel-concrete interface are performed to investigate and determine the mechanical roles and properties of interface parameters. The intrinsic different nature of bonded and unbonded interfaces are addressed based on the experimental observations that were obtained from two types of tests considering bonded and unbonded interfaces. The unbonded tests are performed for the specimens that are in unbonded when the initially bonded specimens are tested first. Four cases of lateral confinements including pure slip, and low and medium levels of lateral pressure are taken into account to investigate the effects of lateral confinements on interface behavior. It is shown that the maximum shear strengths, the levels of residual strengths and the Mode II fracture energy release rates are linearly related to the confinement levels. Based on the experimental evidences obtained from this study, the values of interface parameters required in a steel-concrete interface constitutive model will be presented in the companion paper.
Determination of Steel-concrete Interface Parameters: Me chanical Properties of Interface Parameters
Lee, Ta ; Joo, Young-Tae ; Lee, Yong-Hak ;
Journal of the Korea Concrete Institute, volume 21, issue 6, 2009, Pages 781~788
DOI : 10.4334/JKCI.2009.21.6.781
Mechanical properties of steel-concrete interface were evaluated on the basis of experimental observations. The properties included bond strength, unbounded and bonded friction angles, residual level of friction angle, mode I fracture energy, mode II bonded fracture energy and unbonded slip-friction energy under different levels of normal stress, and shape parameters to define geometrical shape of failure envelope. For this purpose, a typical type of constitutive model of describing steel-concrete interface behavior was presented based on a hyperbolic three-parameter Mohr-Coulomb type failure criterion. The constitutive model depicts the strong dependency of interface behavior on bonding condition of interface, bonded or unbounded. Values of the interface parameters were determined through interpretation of experimental results, geometry of failure envelope and sensitivity analysis. Nonlinear finite element analysis that incorporates steel-concrete interface as well as material nonlinearities of concrete and steel were performed to predict the experimental results.
Mechanical Properties of Concrete with Statistical Variations
Kim, Jee-Sang ; Shin, Jeong-Ho ;
Journal of the Korea Concrete Institute, volume 21, issue 6, 2009, Pages 789~796
DOI : 10.4334/JKCI.2009.21.6.789
The randomness in the strength of a RC member is caused mainly by the variability of the mechanical properties of concrete and steel, the dimensions of concrete cross sections, and the placement of reinforcing bars and so on . Among those variations, the randomness and uncertainty of mechanical properties of concrete, such as compressive strength, tensile strength, and elastic modulus give the most significant influences and show relatively large statistical variations. In Korea, there has been little effort for the construction of its own statistical models for mechanical properties of concrete and steel, thus the foreign data have been utilized till now. In this paper, variability of compressive strength, tensile strength and elastic modulus of normal-weight structural concrete with various specified design compressive strength levels are examined based on the data obtained from a number of published and unpublished sources in this country and additional laboratory tests done by the authors. The inherent probabilistic models for compressive and tensile strength of normal-weight concrete are proposed as Gaussian distribution. Also, the relationships between compressive and splitting tensile strength and between compressive strength and elastic modulus in current KCI Code are verified and new ones are suggested based on local data.
Calculations of Flat Plate Deflections Considering Effects of Construction Loads and Cracking
Kim, Jae-Yo ; Im, Ju-Hyeuk ; Park, Hong-Gun ;
Journal of the Korea Concrete Institute, volume 21, issue 6, 2009, Pages 797~804
DOI : 10.4334/JKCI.2009.21.6.797
The structural designs of RC flat plates that have insufficient flexural stiffness due to lack of support from boundary beams may be governed by serviceability as well as a strength criteira. Specially, since over-loading and tensile cracking in early-aged slabs significantly increase the deflection of a flat plate system under construction, a construction sequence and its impact on the slab deflections may be decisive factors in designs of flat plate systems. In this study, the procedure of calculating slab deflections considering construction sequences and concrete cracking effects is proposed. The construction steps and the construction loads are defined by the simplified method, and then the slab moments, elastic deflections, and the effective moment of inertia are calculated in each construction step. The elastic deflections in column and middle strips are magnified to inelastic deflections by the effective moment of inertia, and the center deflection of slab are calculated by the crossing beam method. The proposed method is verified by comparisons with the existing test result and the nonlinear analysis result. Also, by applications of the proposed method, the effects of the slab construction cycle and the number of shored floors on the deflections of flat plates under construction are analyzed.