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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 27, Issue 6 - Dec 2015
Volume 27, Issue 5 - Oct 2015
Volume 27, Issue 4 - Aug 2015
Volume 27, Issue 3 - Jun 2015
Volume 27, Issue 2 - Apr 2015
Volume 27, Issue 1 - Feb 2015
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Hydration Properties of Ordinary Portland Cement Using Mixture of Limestone and Blast Furnace Slag as Minor Inorganic Additives
Lee, Seung-Heun ; Lim, Young-Jin ; Cho, Jae-Woo ;
Journal of the Korea Concrete Institute, volume 27, issue 1, 2015, Pages 3~9
DOI : 10.4334/JKCI.2015.27.1.003
In this study, hydration properties of ordinary Portland cement were examined, shown from a limestone and blast furnace slag alone or their mixture up to 10% as a minor mineral additives. As of setting time, it was identified that final setting became faster as the amount of limestone mixture increased, which showed limestone accelerated early hydration faster than blast furnace slag. This is because limestone did accelerate the hydration of alite. At the age of 3 days, limestone 5%-blast furnace slag 5% mixture had the highest compressive strength of mortar. It is because hydration acceleration of alite by limestone, and
that was additionally formed by hydration acceleration of alite reacted with blast furnace slag, and as a result, additionally created C-S-H hydrate. Regarding the hydration properties by the age of 7 and 28 days, limestone 3%-blast furnace slag 7% of composited mixture showed the largest compressive strength, and in comparison with the 3 days in curing age. This period is when hydration reaction of blast furnace slag is active and the amount of hydrate depends on the amount of blast furnace slag mixture more than that of the limestone mixture. And in order to vitalize hydration reaction of blast furnace slag the amount of
created has to increase, and thus, a small amount of limestone is necessary that can accelerate the hydration of alite. Therefore, after the age of 7 days, the fact that there were a large amount of blast furnace slag mixture and small amount of limestone mixture was effective to the strength development of ordinary Portland cement.
Development and Performance Test for Unbonded Post-Tensioned Anchor
Cho, Ah Sir ; Jo, Yeong Wook ; Jeon, Byong Kap ; Kang, Thomas H.K. ;
Journal of the Korea Concrete Institute, volume 27, issue 1, 2015, Pages 11~20
DOI : 10.4334/JKCI.2015.27.1.011
An unbonded post-tensioned anchor using a 15.2 mm diameter 7-wire strand was developed based on finite element analysis and experimental testing. In order to evaluate its performance, static load tests and load transfer tests were conducted following KCI-PS101. The static load tests and additional strand tensile tests confirmed that the developed anchor had a capacity more than nominal tensile strength of a 7-wire strand without any damage or deterioration. According to the result of load transfer tests for many different reinforcing details, specimens with no additional reinforcing bars sustained at least 1.64 times the nominal tensile strength of the strand.
Micro-silica Mixed Aqua-epoxy for Concrete Module Connection in Water : Part 1 - Material Development and Evaluation
Choi, Jin-Won ; Kim, Young-Jun ; You, Young-Jun ; Kwon, Seung-Jun ; Kim, Jang-Ho Jay ;
Journal of the Korea Concrete Institute, volume 27, issue 1, 2015, Pages 21~28
DOI : 10.4334/JKCI.2015.27.1.021
Recent studies on concrete floating structure development focused on connection system of concrete modules. Precast concrete modules are designed to be attached by prestressing in the water, exposing the structure to the loads from water and making the construction difficult. Therefore, a development of bond material became a key issue in successful connection of floating concrete modules. In this study, micro-silica mixed aqua epoxy (MSAE) is developed for the task. Existing primer aqua epoxy, originally used as a bond material for the retrofit of concrete structures using fiber reinforced polymers, is evaluated to find the optimum micro-silica added mix proportion. Micro-silica of 0~4 volume % was mixed in standard mixture of aqua epoxy. Then, the material property tests were performed to study the effect of micro-silica in aqua epoxy by controlling the epoxy silane proportion by 0,
. The optimum mix design of MSAE was derived based on the test results. The MSAE was used to connect concrete module specimens with the epoxy thickness variation of 5, 10, and 20mm. Then, 3-point loading test was performed to verify the bond capacity of MSAE. The results show that MSAE improves the bond capacity of concrete module.
Micro-silica Mixed Aqua-epoxy for Concrete Module Connection in Water : Part 2 - Structural Application and Evaluation
Choi, Jin-Won ; You, Young-Jun ; Jeong, Youn-Ju ; Kwon, Seung-Jun ; Kim, Jang-Ho Jay ;
Journal of the Korea Concrete Institute, volume 27, issue 1, 2015, Pages 29~35
DOI : 10.4334/JKCI.2015.27.1.029
Recent studies to develop Very Large Floating Structure(VLFS) has shown that the construction procedure of the structure needs to acquire precast concrete module connection system using prestressing. However, the loads occurring on water are complex combinations of various condition, so the safe and stable performance of the module joints and bonding materials are key to the success of the construction. Therefore, micro-silica mixed aqua-epoxy development was introduced in Part 1 using a bonding material developed in this study. The performance of the micro-silica mixed aqua-epoxy(MSAE) applied joint of concrete module specimens connected by prestressing tendon was evaluated to verify the usability and safety of the material. RC beam, spliced beam connected by prestressing tendon and MSAE, and continuous prestressed concrete beam were tested for their initial cracking and maximum loads as well as cracking procedure and pattern. The results showed that the MSAE can control the stress concentration effect of the shear key and the crack propagation, and the maximum load capacity of MSAE joint specimens are only 5% less than that of continuous RC specimen. The details of the study are discussed in detail in the paper.
Cracking Behavior and Flexural Performance of RC Beam with Strain Hardening Cement Composite and High-Strength Reinforcing Bar
Jang, Seok-Joon ; Kang, Su-Won ; Yun, Hyun-Do ;
Journal of the Korea Concrete Institute, volume 27, issue 1, 2015, Pages 37~44
DOI : 10.4334/JKCI.2015.27.1.037
This paper describes the effect of strain hardening cement composite (SHCC) material on structure performance of reinforced concrete (RC) beams with high-strength reinforcing bar. Also, this paper explores the structure application of SHCC in order to mitigation cracking damage and improve the ductility of flexural RC members. The prediction model for flexural strength of doubly reinforced SHCC beams are investigated in this study. To achieve the these objectives, a total of 6 rectangular beam specimens were tested under four point monotonic loading condition. The main parameters included the types of cement composite and reinforcing bar. Test results indicated that reinforced beam specimens with SHCC material were improved the structure performances and damage characteristics. Specifically, replacement of conventional high-strength concrete with SHCC materials has the potential of high-strength steel bar as flexural reinforcement on RC members. It is remarkable that suggested method of reinforced SHCC beams with high-strength reinforcing bar could be used usefully to the structure design.
Confinement Effect of Reinforced Concrete Members Using a Parabola-Rectangular Compressive Stress-Strain Relationship
Choi, Seung Won ; Kim, Woo ;
Journal of the Korea Concrete Institute, volume 27, issue 1, 2015, Pages 45~53
DOI : 10.4334/JKCI.2015.27.1.045
In general, RC columns are reinforced by spiral or tied steel and a strength of confined concrete is more increased than this of unconfined concrete. And strength and ductility of column are increased by a confinement effect. A confinement effect is affected by concrete strength, spacing, volume and strength of confinement steel. Many researchers suggested various confinement models which reflected these parameters by many experimental results. In this study, a load-strain relationship is evaluated by a confinement model in EC2, and it is compared with Mander model, Saatchioglu-Razvi model and Cusson et al. model. As results, it is appeared that a confinement model in EC2 is able to apply all kinds of concrete strength and a consistency in sectional analysis can be secured using material models in EC2. In parameter studies using material models in EC2, a confinement effect is more affected by a confinement steel than a concrete strength.
Evaluation of Structural Performance of Precast Modular Pier Cap
Kim, Dong Wook ; Shim, Chang Su ;
Journal of the Korea Concrete Institute, volume 27, issue 1, 2015, Pages 55~63
DOI : 10.4334/JKCI.2015.27.1.055
Prefabrication technologies are making bridge construction safer and less disruptive to the environment and traveling public, making bridge designs more constructible and, improving the quality and durability by shifting site work to a more controllable environment. Modular bridge substructures with concrete-filled steel tube (CFT) piers and composite pier caps were suggested to realize accelerated bridge construction. The precast segmental pier cap consists of a composite pier table and precast prestressed segments on the table. The pier table has embedded steel section to mitigate stress concentration at the connection by small tubes. Each bridge pier has four or six CFT columns which connect to the pier cap. Shear strength of the pier cap was obtained by extending vertical reinforcing bars from the table to the precast segment. Transverse prestressing was introduced to control tensile stresses by service loadings. Structural performance of the proposed modular system was evaluated by static tests. Design requirements of the composite pier cap were satisfied by continuous reinforcing bars and prestressing tendons. Standardized modular substructures can be effectively utilized for the fast replacement or construction of bridges.
Pozzolanicity of Calcined Sewage Sludge with Calcination and Fineness Conditions
So, Hyoung-Seok ; So, Seung-Young ; Khulgadai, Janchivdorj ; Kang, Jae-Hong ; Lee, Min-Hi ;
Journal of the Korea Concrete Institute, volume 27, issue 1, 2015, Pages 65~73
DOI : 10.4334/JKCI.2015.27.1.065
This study discussed the pozzolanic properties of calcined sewage sludge (CSS) according to calcination and fineness conditions. The chemical and mineralogical analysis of CSS according to calcination temperature and time were carried out and compared with that of the existing pozzolanic materials such as fly-ash, blast furnance slag and meta-kaolin. Various mortars were made by mixing those CSS and
(1:1 wt. %), and their compressive strength and hydrates according to experimental factors such as fineness of CSS and curing age were also investigated in detail. The results show clearly the potentiality of calcined sewage sludge (CSS) as an admixture materials in concrete, but the CSS should be controlled by calcination temperature and time, and fineness etc. In this experimental condition, the calcination temperature of
, calcination time of 2 hours and fineness of
were optimum conditions in consideration of the mechanical properties and economic efficiency of CSS. The compressive strength of CSS mortars was higher than that of fly-ash mortars and blast furnace slag mortars, especially at the early ages. Then, the utilization of CSS in construction fields was greatly expected.
Antifungal Performance of Hwangtoh Mortars with Natural Antifungal Substances
So, Hyoung-Seok ; Kim, Jung-Woo ; Lee, Bo-Ram ; So, Seung-Young ;
Journal of the Korea Concrete Institute, volume 27, issue 1, 2015, Pages 75~83
DOI : 10.4334/JKCI.2015.27.1.075
This study discusses the long-term antifungal effect and antifungal performance of Hwangtoh mortars with various natural antifungal substances on five types of mold: Chaetomium globosum, Aspergillus niger, Aureobasidium pullulans, Gliocladium virens, and Penicillium pinophilum, which can be easily detected in the indoors and outdoors of buildings in damp environments. The antifungal performances of various natural antifungal substances extracted from Marjoram, Phytoncide, Thyme, Ginkgo leaves, and Chitosan (oligosaccharide) were investigated on the five types of mold, as a basic experiment. Using the natural antifungal substances selected for the basic experiment, antifungal mortars were made, and their antifungal performance and long-term antifungal effects were also investigated. The results clearly showed that the marjoram extract and their associated mortars had excellent antifungal performance. Also, their long-term antifungal effects were outstanding and at an equivalent level to those of the mortars with organic chemical antifungal agents. The optimum addition rate of the marjoram extract in the mortar was 5% by mass of binder. It was also shown that the phytoncide extract in the mortar needed an addition rate of more than 10% according to the mass of binder, considering the long-term antifungal effect and the antifungal performance.
Analysis on Adsorption Rate & Mechanism on Chloride Adsorption Behavior with Cement Hydrates
Yoon, In-Seok ;
Journal of the Korea Concrete Institute, volume 27, issue 1, 2015, Pages 85~92
DOI : 10.4334/JKCI.2015.27.1.085
The chloride ions, responsible for the initiation of the corrosion mechanism, intrude from the external medium into the concrete. A part of the intruding chloride ions will be retained by the hydration products of the binder in concrete, either through chemical adsorption or by physical adsorption. Since the hydration products of cement are responsible for the chloride binding in concrete, this study focused on the chloride binding in individual hydrate. The purpose of this study is to explore the time dependant behaviors of chloride ions adsorption with cement hydrates, focused on its mechanism. AFt phase and CH phase were not able to absorb chloride ion, however, C-S-H phase and AFm phase had a significant chloride adsorption capacity. In particular, AFm phase showed a chemical adsorption with slow rate in 40 days, while C-S-H phase showed binding behaviors with 3 stages including momentary physical adsorption, physico-chemical adsorption, and chemical adsorption. Based on the results, this study suggested theoretical approach to depict chloride adsorption behavior with elapsed time of C-S-H phase and AFm phase effectively. It is believed that the approach suggested in this study can provide us with a good solution to understand the mechanism on chloride adsorption with hydrates and to calculate a rate of chloride penetration with original source of chloride ions, for example, marine sand at initial time or sea water penetration later on.