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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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Behavior and Capacity of Compression Lap Splice in Confined 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 4, 2009, Pages 389~400
DOI : 10.4334/JKCI.2009.21.4.389
A compression lap splice can be calculated longer than a tension lap splice in high strength concrete according to current design codes. Including effects of transverse reinforcement, a compression splice becomes much longer than a tension splice. Effects of transverse reinforcement and bar size on strength and behavior of compression lap splice, which always exist in actual structures, have been investigated through experimental study of column tests with concrete strength of 40 and 60 MPa. The results of the tests with bar diameters of 22 and 29 mm show that there is no size effect of bar diameter on compression lap splice. Bond strength of small bar diameter may increase. However, large diameters of re-bars are used in compression member and the size effect of re-bars does not have to be considered in compression lap splice. Confined specimens have twice of calculated strengths by current design codes. New design equations for the compression lap splice including the effects of transverse reinforcement are required for practical purpose of ultra-high strength concrete. End bearing is enhanced by transverse reinforcement placed at ends of splice not by transverse reinforcement within splice length. As more transverse reinforcement are placed, the stresses developed by bond linearly increase. The transverse reinforcements at ends of splice a little improve the strength by bond. Because the stresses developed by bond in compression splice with transverse reinforcement are nearly identical to or less than those in tension splice with same transverse reinforcement, strength increment of compression splice is attributed to end bearing only.
Compression Lap Splice Length in Concrete of Compressive Strength from 40 to 70 MPa
Chun, Sung-Chul ; Lee, Sung-Ho ; Oh, Bo-Hwan ;
Journal of the Korea Concrete Institute, volume 21, issue 4, 2009, Pages 401~408
DOI : 10.4334/JKCI.2009.21.4.401
A compression lap splice becomes an important issue due to development of ultra-high strength concrete. Current design codes regarding compression lap splice do not utilize merits of the improved strength of ultra-high strength concrete. Especially, a compression lap splice can be calculated longer than a tension lap splice according to the codes because they do not consider effects of compressive strength of concrete and transverse reinforcement. This anomaly confuses engineers in practice. Design equation is proposed for compression lap splice in 40 to 70 MPa of compressive strength of concrete. The proposed equation is based on 51 specimens conducted by authors. Basic form of the equation includes main parameters which are derived from investigating test results. Through two-variable non-linear regression analysis of measured splice strengths, a strength equation of compression lap splices is then derived. A specified splice strength is defined using a 5% fractile coefficient and a lap length equation is constructed. By the proposed equation, the anomaly of lap lengths in tension and compression is got rid of. In addition, the equation has a reliability equivalent to those of the specified strengths of materials.
Experimental Study on Artificial Crack Healing for Concrete Using Electrochemical Deposition Method
Lee, Chang-Hong ; Song, Ha-Won ;
Journal of the Korea Concrete Institute, volume 21, issue 4, 2009, Pages 409~417
DOI : 10.4334/JKCI.2009.21.4.409
In this study, autogenous crack healing and artificial crack healing using electrochemical electro deposition method were conducted to compare in the aspects of corrosion monitoring. Furthermore, the analysis of impressed voltage characteristics, galvanic current and linear polarization resistance comparison, and photo image processing technique were performed for quantitative comparisons of healing ratio. As a result, it was found that, in view of impressed voltage of artificial crack healing, the measured voltage was increased as time goes by. From the galvanic test results of artificial crack healing, the current vs. potential distribution value were formed widely in comparison with autogenous crack healing. In this point, it was shown that artificial crack healing has more eleatic resistance capacity than autogenous crack healing technique. Finally, it was found that artificial crack healing was 1.63 times higher than autogenous healing in view of crack healing ratio.
Investigation of Stress Changes in Concrete and Strands according to Cutting Order of the Strands in Pre-tensioned Concrete Slab
Moon, Do-Young ; Kim, Jang-Ho ; Kim, Gyu-Seon ; Yun, Man-Geun ; Zi, Goang-Seup ;
Journal of the Korea Concrete Institute, volume 21, issue 4, 2009, Pages 419~429
DOI : 10.4334/JKCI.2009.21.4.419
This study focuses on the effect of the cutting order of prestressing strands on the strain change in the strands and on the state of stress of concrete, experimentally and numerically. In the experiment, strain of strands and of transversal reinforcement were measured for three different cutting orders during detensioning process by using flame-cutting procedure. The experimental results were compared with those obtained from the FE analysis. As a results of the experiment, it is confirmed that the cutting order of prestressing strands affected on the strain of strands as well as of transversal reinforcement. The FE analysis gave similar results to those obtained from the experiment. Therefore, the cutting order should be chosen appropriately to when the strands get detensioned.
Flexural Behavior of Reinforced Recycled Aggregate Concrete Beams
Song, Seon-Hwa ; Choi, Ki-Sun ; You, Young-Chan ; Kim, Keung-Hwan ; Yun, Hyun-Do ;
Journal of the Korea Concrete Institute, volume 21, issue 4, 2009, Pages 431~439
DOI : 10.4334/JKCI.2009.21.4.431
These days the amount of demolished concrete waste has been increasing due to reconstruction and redevelopment of aged buildings. So the use of recycled aggregates is recommended to solve environmental problems. Some investigations have been carried out to study the flexural behavior of reinforced concrete beams with recycled aggregates. But these have some limitation due to the use of low quality recycled aggregates and small-scale specimens in the laboratory. The purpose of this experimental study is to evaluate the flexural behavior of simply supported RC beams subjected to four-point monotonic loading and made with recycled aggregates. Seven full-scale RC beams were manufactured with different replacement level of recycled aggregates. The main parameters of the study are combination of aggregates. From the test results, the flexural behavior of the beam is described in terms of crack patterns and failure modes. And the flexural strength of RC beam with different types of recycled coarse aggregates and recycled fine aggregates is compared with the provision of KCI code.
Selection of Portland Cement for Prevention of Sulfate Attack-Part 1 Sodium Sulfate Attack
Kim, Jong-Pil ;
Journal of the Korea Concrete Institute, volume 21, issue 4, 2009, Pages 441~447
DOI : 10.4334/JKCI.2009.21.4.441
This paper presents a detailed experimental study on the sulfate resistance of specimens made with portland cement exposed to sulfate attack. The mortar specimens were immersed in a 5% sodium sulfate solution for 360 days and regularly monitored for visual damage, compressive strength loss and expansion. In addition, at the end of 360 days, the products of sulfate attack and the mechanism of attack were investigated through X-ray diffraction, TG&DSC and scanning electron microscopy. The test results indicated that the sulfate deterioration data was ordinary portland cement > sulfate resistance portland cement > low heat portland cement. The microstructural studies indicated that the main reaction product of deterioration of the mortar specimens was the formation of ettringite, gypsum and thaumasite due to sulfate attack. For portland cement matrices, a low heat cement matrix containing the lowest C3A and silicate ratio (C/S) was beneficient against the sulfate attack.
A Study on the Carbonation Characteristics of Fly Ash Concrete by Accelerated Carbonation Test
Choi, Sung ; Lee, Kwang-Myong ; Jung, Sang-Hwa ; Kim, Joo-Hyung ;
Journal of the Korea Concrete Institute, volume 21, issue 4, 2009, Pages 449~455
DOI : 10.4334/JKCI.2009.21.4.449
The increase of industrial carbonic dioxide emissions has accelerated the carbonation of reinforced concrete structures, which drops off their durability. Although advanced countries have already taken safety control measures against the carbonation of RC structures, it is still difficult now to accurately predict the actual carbonation depth. Additionally, it requires much time and efforts. Recently, it is possible to get the data more rapidly through accelerated carbonation test with the
concentration of 100%. In this paper, the carbonation test results obtained by two test methods such as the normal carbonation test method and the accelerated carbonation test method, were compared to investigate the carbonation characteristics of fly ash concrete. The accelerated carbonation test on concrete specimens with the pre-curing age of 180 days was also carried out to examine the carbonation characteristics of fly ash concrete at long-term age. Consequently, fly ash concrete at early age was vulnerable to carbonation and however, its carbonation resistance at long-term ages was improved compared with OPC concrete.
Quantitative Damage Evaluation of Fiber-Reinforced Cement Composite Using Acoustic Emission Technique
Lee, Young-Oh ; Yun, Yeo-Jin ; Yun, Hyun-Do ;
Journal of the Korea Concrete Institute, volume 21, issue 4, 2009, Pages 457~464
DOI : 10.4334/JKCI.2009.21.4.457
Fiber is an important ingredient in fiber-reinforced cement composite (FRCC) which can control fracture of cement composite by bridging action. In compliance with the action of the fiber and the aggregate size, it also showed a different failure mechanism. For practical application, it is needed to investigate the fracture behavior of the FRCC and to understand the micro-mechanism of cement matrix with reinforcing fiber. In order to evaluate a characteristics of fracture process in the FRCC, acoustic emission (AE) technique was used for the analysis and evaluation of FRCC damage by acoustic emission under flexural and cyclic compressive loadings. The AE signals were monitored by AMSY4 AE instrument during the entire loading period. The specimens are reinforced with 0, 1.0, 1.5 and 2.0% (by volume) Polyvinyl alcohol (PVA) fiber. The test results showed that the damage progress of the FRCC was characteristic for the fiber replacement ratio. As a result of analyzing the felicity ratio (FR) values, it is shown that this values can be used for evaluating the degree of FRCC damage. On the whole the felicity ratio values of FRCC are shown between 0.4 and 1.1. And, the AE kaiser effect was shown in the all FRCC specimen. In addition, the damage behavior and the microscopic fracture process of the FRCC are evaluated using the AE parameters, such as calm ratio, b-value and felicity ratio. The purpose of this reserch was to advance the state of knowledge regarding the applicability of acoustic emission as an evaluation method for FRCC.
Fire Test of Fiber Cocktail Reinforced High Strength Concrete Columns without Loading
Youm, Kwang-Soo ; Jeon, Hun-Kyu ; Kim, Heung-Youl ;
Journal of the Korea Concrete Institute, volume 21, issue 4, 2009, Pages 465~471
DOI : 10.4334/JKCI.2009.21.4.465
To prevent the explosive spalling of the high strength concrete and control the rise of temperature in the steel rebar during fire, a fiber cocktail method has been proposed simultaneously with the use of polypropylene and steel fiber. After applying the fiber cocktail (polypropylene and steel fibers) into the mixture of high strength concrete with a compressive strength of between 40 and 100 MPa and evaluating the thermal properties at elevated temperatures, the fire test was carried out on structural members in order to evaluate the fire resistance performance. Two column specimens were exposed to the fire without loading for 180 minutes based on the standard curve of ISO-834. No explosive spalling has been observed and the original color of specimen surface was changed to light pinkish grey. The inner temperature of concrete dropped rapidly starting from 60mm deep. After 60 minutes of exposure to the fire, the temperature gradient of fiber cocktail reinforced high strength concrete was measured as 2.2oC/mm, which is approximately 5 times less than that of normal concrete. The final temperatures of steel rebar after 180 minutes of fire test resulted in 488.0oC for corner rebar, 350.9oC for center rebar, and 419.5oC for total mean of steel rebar. The difference of mean temperature between corner and center rebar was 137.1oC The tendency of temperature rise in concrete and steel rebar changed between 100oC and 150oC The cause of decrease in temperature rise was due to the water vaporization in concrete, the lower temperature gradient of the concrete with steel and polypropylene fiber cocktails, the moisture movement toward steel rebars and the moisture clogging.
Fire Test of Fiber Cocktail Reinforced High Strength Concrete Columns with Loading
Youm, Kwang-Soo ; Jeon, Hun-Kyu ; Kim, Heung-Youl ;
Journal of the Korea Concrete Institute, volume 21, issue 4, 2009, Pages 473~480
DOI : 10.4334/JKCI.2009.21.4.473
The 180 minutes fire test based on the standard curve of ISO-834 were conducted on three RC column specimens with different constant axial loading ratios to evaluate the fire performance of fiber cocktail (polypropylene+steel fiber) reinforced high strength concrete column. The columns were tested under three loading levels as 40%, 50%, and 61% of the design load. No explosive spalling has been observed and the original color of specimen surface has been changed to light pinkish grey. The maximum axial displacements of three specimens were 1.5~2.2 mm. There was no reduction in load bearing capacity of each specimen exposed to fire and no effect were observed on the fire performance within 61% of the design load. The tendencies of the results with loading, such as the temperature distribution of in concrete and the changes in temperature rise due to the water vaporization in concrete, are very similar to those without loading. The final temperatures of steel rebar after 180 minutes of fire test resulted in 491.4
for corner rebar, 329.0
for center rebar, and 409.8
for total mean of steel rebar. The difference of mean temperature between corner and center rebar was 153.7
ㅍ. The tendency of temperature rise in concrete and steel rebar changed after 30~50 minutes from the starting time of the fire test because the heat energy influx into corner rebar is larger than that into center rebar. The cause of decrease in temperature rise was due to the water vaporization in concrete, the lower temperature gradient of the concrete with steel and polypropylene fiber cocktails, the moisture movement toward steel rebars and the moisture clogging.
The Analysis of Early Age Properties of Hydration Heat and Autogenous Shrinkage according to Specimen Size and Retardation of Hydration
Kim, Gyu-Yong ; Koo, Kyung-Mo ; Lee, Hyoung-Jun ; Lee, Eui-Bae ;
Journal of the Korea Concrete Institute, volume 21, issue 4, 2009, Pages 481~488
DOI : 10.4334/JKCI.2009.21.4.481
It has been reported that the magnitude and the development rate of autogenous shrinkage of cement paste, mortar and concrete were affected by history and magnitude of inner temperature at an early age. But it was not enough to explain the relation between hydration heat and autogenous shrinkage at an early age, because there was no certain analysis on histories of hydration heat and autogenous shrinkage in previous studies. In our prior study, to understand the relationship between hydration heat and autogenous shrinkage of concrete at an early age, the analysis method for histories of hydration heat and autogenous shrinkage was suggested. Based on this method, early age properties of hydration heat and autogenous shrinkage of high strength concrete with different sizes and hydration retardation were investigated in this study. As a result of the study, properties of hydration temperature and autogenous shrinkage were different according to specimen size and hydration retardation. However, there was a close relationship between hydration temperature and autogenous shrinkage at an early age, especially between HHV and ASV as linear slopes of the sections where hydration temperature and autogenous shrinkage increase rapidly; the higher HHV, the higher ASV and the greater ultimate autogenous shrinkage. And it was found that, among the setting time, bend point and temperature increasing point, they were close relationship each other on cement hydration process.
Ultimate Stress of Unbonded Tendons in Post-Tensioned Flexural Members
Lee, Deuck-Hang ; Kim, Kang-Su ;
Journal of the Korea Concrete Institute, volume 21, issue 4, 2009, Pages 489~499
DOI : 10.4334/JKCI.2009.21.4.489
It is quite difficult to predict the flexural strength of post-tensioned members with unbonded tendons (unbonded posttensioned members, UPT members) because of debonding behavior between concrete and prestressing tendons, which is different from that with bonded tendons. Despite many previous researches, our understanding on the flexural strength of UPT members is still insufficient, and thus, national codes use different methods to calculate the strength, which quite often give very different results. Therefore, this paper reviews various existing methods, and aims at proposing an improved rational strength model for UPT flexural members having better accuracy. Additionally, a database containing a large number of test data on UPT flexural members has been established and used for verification of the proposed flexural strength model. The analysis results show that the proposed method provides much better accuracy than many existing methods including the rigid-body model that utilizes the assumption of concentrated deformation and plastic hinge length, and that it also gives proper consideration on the effects of primary parameters such as reinforcement ratio, loading pattern, concrete strength, etc. Especially, the proposed method also well predicts the ultimate stress of unbonded tendons of over-reinforced members, which are often possible in construction fields, and high strength concrete members.
A Study on the Development of Self-Healing Smart Concrete Using Microbial Biomineralization
Kim, Wha-Jung ; Kim, Sung-Tae ; Park, Sung-Jin ; Ghim, Sa-Youl ; Chun, Woo-Young ;
Journal of the Korea Concrete Institute, volume 21, issue 4, 2009, Pages 501~511
DOI : 10.4334/JKCI.2009.21.4.501
This study was conducted to develop self-healing ability of concrete so that inspection could be available even in the event of minute cracks without complex works at any time for more economic concrete structure maintenance and longevity. A completely different method has been carried out in comparison with many of similar researches on self-healing concrete. This is a basic study on the development of self-healing concrete using microbial biomineralization. Compounds were generated except for cells by precipitation reaction of CaC
during the microbial metabolism and we examined the use as a binder that hardens the surface of sand using biomineralization that Sporosarcina pasteurii precipitates CaC
. In result, the formation of new mineral and hardening of sand surface could be verified partly, and it was available for cracks to be repaired by calcite with organic (microorganism) and inorganic (CaC
) complex structure through the basic experiment a little bit. Therefore the use of biomineralization by this sort of microbial metabolism for concrete structure helps to develop absolute repair-concrete like this concrete with microorganism. The effect of microbial application will be one of the most important research tasks having influence on not only repair for concrete structure but also development of new materials able to reduce environmental problems.
Experiment of Flexural Behavior of Prestressed Concrete Beams with External Tendons according to Tendon Area and Tendon Force
Yoo, Sung-Won ; Yang, In-Hwan ; Suh, Jeong-In ;
Journal of the Korea Concrete Institute, volume 21, issue 4, 2009, Pages 513~521
DOI : 10.4334/JKCI.2009.21.4.513
Recently, the externally prestressed unbonded concrete structures are increasingly being built. The mechanical behavior of prestressed concrete beams with external unbonded tendon is different from that of normal bonded PSC beams in that the slip of tendons at deviators and the change of tendon eccentricity occurs as external loads are applied in external unbonded PSC beams. The purpose of the present paper is therefore to evaluate the flexural behavior by performing static flexural test according to tendon area and tendon force. From experimental results, before flexural cracking, there was no difference between external members and bonded members. However, after cracking, yielding load of reinforcement, ultimate load, and the tendon stress of external members was lower than that of bonded members. For the relationship of load-tendon stress, the increasing of tendon strain was inversely proportional to the initial tendon force. However, even if the initial tendon force was large, the tendon strain with small effective stress was smaller than that with large effective stress. The concrete compressive strain was proportional to the effective stress of external tendon. From the comparison between test results and codes, the ACI-318 could not consider the effect of tendon force or effective stress, and especially the results of ACI-318 were very small, so it was very conservative. And the AASHTO 1994 could be influenced on the tendon area, initial force and effective stress, but as it was made on the basis of internal unbonded tendon, its results were much larger than the test results. For this reason, the new correct predict equation of external tendon stress will be needed.
Improved Biaxial Flexure Test (BFT) for Concrete with the Optimum Specimen Geometry
Zi, Gooang-Seup ; Kim, Ji-Hwan ; Oh, Hong-Seob ;
Journal of the Korea Concrete Institute, volume 21, issue 4, 2009, Pages 523~530
DOI : 10.4334/JKCI.2009.21.4.523
For designing concrete structures, engineers are provided data from unidirectional flexure test in most cases. But real structural components such as pavements and deck panel are subjected to multiaxial stress throughout their body. Therefore, biaxial flexure test for concrete may be considered as a gage of the performance of concrete in service. In this paper, we propose the optimum biaixial flexture test (BFT) to measure the biaxial flexural strength of concrete. This method are an improved version of the ring-on-ring test which have been used extensively in the fields of ceramics and biomaterials. The optimum geometry of the test specimen was determined by using a three-dimensional finite element analysis. A series of test data obtained from the proposed test method is provided to show that the proposed optimum biaxial flexure test method can be used to identify the biaxial tensile strength of concrete.
Microstructural Study of Mortar Bar on Akali-Silica Reaction by Means of SEM and EPMA Analysis
Jun, Ssang-Sun ; Lee, Hyo-Min ; Jin, Chi-Sub ;
Journal of the Korea Concrete Institute, volume 21, issue 4, 2009, Pages 531~537
DOI : 10.4334/JKCI.2009.21.4.531
In this study alkali reactivity of crushed stone was conducted according to the ASTM C 227 that is traditional mortar bar test, and C 1260 that is accelerated mortar bar test method. The morphology and chemical composition of products formed in mortar bar, 3 years after the mortar bar tests had been performed, were examined using scanning electron microscopy (SEM) with secondary electron imaging (SEI) and electron probe microanalysis (EPMA) with backscattered electron imaging (BSEI). The crushed stone used in this study was not identified as being reactive by ASTM C 227. However, mortar bars exceeded the limit for deleterious expansion in accelerated mortar bar test used KOH solution. The result of SEM (SEI) analysis, after the ASTM C 227 mortar bar test, confirmed that there were no reactive products and evidence of reaction between aggregate particles and cement paste. However, mortar bars exposed to alkali solution (KOH) indicated that crystallized products having rosette morphology were observed in the interior wall of pores. EPMA results of mortar bar by ASTM C 227 indicated that white dots were observed on the surface of particles and these products were identified as Al-ASR gels. It can be considered that the mortar bar by ASTM C 227 started to appear sign of alkali-silica reaction in normal condition. EPMA results of the mortar bar by ASTM C 1260 showed the gel accumulated in the pores and diffused in to the cement matrix through cracks, and gel in the pores were found to be richer in calcium compared to gel in cracks within aggregate particles. In this experimental study, damages to mortar bars due to alkali-silica reaction (ASR) were observed. Due to the increasing needs of crushed stones, it is considered that specifications and guidelines to prevent ASR in new concrete should be developed.