• Proceedings of the Korean Institute of Building Construction Conference
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• 2020.11a
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• pp.75-76
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• 2020

In this study, in order to check whether the adhesion strength can be secured when installing concrete by mixing super-retarding agents, the splitting tensile strength of the joints of each mold was measured and then analyzed. The results of the experiment showed that the bonding performance of the joint is adversely affected if the installation delay is delayed for more than 24 hours, and that the attachment performance can be secured if the installation is delayed within about 24 hours.

• Journal of the Korea institute for structural maintenance and inspection
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• v.21 no.2
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• pp.103-113
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• 2017

In the current study, retarding type and standard type admixture design of concrete have been proposed to control the generation of hydration heat for foundation members that use high strengths concrete. Finite element analysis also has been conducted to understand the rational placing heights of concrete. In addition, real-size structures have experimented and their results were compared to the analytical results to evaluate the reducing effect of thermal stress. For a large $6.5m{\times}6.5m{\times}3.5m$ member with retarding and standard type horizontal partition placement of concrete showed the manageable possibility of temperature difference within 25-degree Celcius between the middle and surface portion while the maximum temperature was 77-degree Celcius. Also, temperature cracking index from the finite element analysis appeared to be 1.49 that predicts no formation of cracking due to the effects of temperature. Finally, it appeared that horizontal partition placement of retarding and standard type concrete has the significant effect of reducing the thermal stress that generated by the hydration heat in the high strengths mass concrete.

• Proceedings of the KAIS Fall Conference
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• 2011.05a
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• pp.471-473
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• 2011

도로경계석과 측구는 차도와 인도의 구분에 의해 주행하는 차량으로부터 인도의 보행자를 보호하고 강우 시 노면의 배수를 용이하게 하기 위한 도로시설물로서 그의 시공품질은 보행자의 안전은 물론 도시미관의 측면에서 매우 중요하다. 그러나 기존의 시공법은 콘크리트를 몇 회로 나누어 분할 타설하는 방법을 사용함으로써 시공불량에 의해 도로경계석이 원 위치에서 이탈하거나 기울어지는 사례가 종종 발생하고 있다. 이러한 문제점들을 해결하고 시공품질을 높이기 위하여 도로경계석과 측구의 일체형 시공법으로써 거푸집 레일과 두 가지 형태의 지그를 사용하는 방법이 최근 제안되었으며 본 연구에서는 새로운 표면처리장치의 개발에 의해 콘크리트 측구의 표면처리방법을 개선하고자 한다.

• Journal of the Korea Concrete Institute
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• v.16 no.2 s.80
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• pp.155-162
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• 2004

An analytical method to predict the time dependent flexural behavior of composite girder is presented based on sectional analysis. The time dependent constitutive relation accounting for the early-age concrete properties including maturing of elastic modulus, creep and shrinkage is derived in an incremental format by the first order Taylor series expansion. The sectional analysis calculates the axial and curvature strains based on the force and moment equilibriums. The deflection curve of the girder approximated by the quadratic polynomial function is calculated by applying to the proper boundary conditions in the consecutive segments. Numerical applications are made for the 3-span double composite steel box girder which is a composite bridge girder filled with concrete at the bottom of the steel box in the negative moment region. The calculated results are compared with those by finite element analysis results. Close agreement is observed between the two approaches.

• Journal of the Korea Concrete Institute
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• v.13 no.4
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• pp.336-345
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• 2001

The construction of underwater structures has been increased, but underwater concrete hassome problems of quality deterioration and contamination around in-situ of civil and architecture; therefore, new materials and methods for them are demanded. In this paper in-situ application of underwater antiwashout concrete which is manufactured for trio purpose of not only decreasing suspended solids and the heat of hydration but also increasing long term strength was studied. In the case of mock-up test(Ⅰ), when underwater antiwashout concrete, whose slump flow was 58 cm, was placed in the mock-up test at a speed of 24 ㎥/hr, it took about a minute to flow to the side wall, and the surface was maintained at horizontal level. In this case, compressive strength of the core specimens in each section was higher than the standard design compressive strength of 240 kgf/㎠. In the case of mock-up test(II), pH value and suspended solids of high strength underwater antiwashout concrete were 10.0∼11.0 and 51 mg/ℓ at 30 minutes later, initial and final setting time were about 30, 37 hr, and the slump flow of that was 53$\pm$2 cm. In the placement at a speed of 27 ㎥/hr, there was no large difference in flowing velocity, with or without reinforcement and flowing slope was maintained at horizontal level. In this case, compressive strength and elastic modulus of the core specimens somewhat decreased as flowing distance was far : however, those of central area showed the highest value.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.30 no.6A
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• pp.525-534
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• 2010

A road curbstone is a structure installed at the boundary of the sidewalk and the street with the objectives of road drainage, drawing attention and such. The current general construction method of curbstones places foundation concrete for the curbstones first, waits until the concrete reaches the strength to support the curbstones, places the curbstones on top, and then places the gutter and rear filling concrete. Such method has the issues of poor compaction and weakened bond strength of concrete due to split placing of concrete, and causes the curbstones to easily separate due to vehicle impact or earth pressure, in turn creating maintenance costs and spoiling the aesthetics. To improve such conventional construction methods, an all-in-one method was developed using formwork rail and jig where both the curbstones and gutter can be worked at the same time, and to evaluate the structural performance, static tests of lateral loading test, pullout test, and bending test were executed, and dynamic tests such as pendulum test and actual vehicle impact test were executed. In all tests, the all-in-one construction method using formwork rail and jig was shown to be superior to the conventional construction method by the increase of construction quality and bond strength of concrete.

• Journal of the Korea Concrete Institute
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• v.23 no.6
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• pp.773-780
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• 2011

In this study, thermal stress analysis are carried out considering material properties, curing condition, ambient temperature, and casting date of the mass concrete placed in bottom slab and side wall of the in-ground type LNG tank as a super massive structure. Also, based on the numerical results, cracking possibility is predicted and counter measures to prevent the cracking are proposed. For the tasks, two optimum mix proportions were selected. From the results of the thermal stress analysis, the through crack index of 1.2 was satisfied for separately caste concrete lots except for the bottom slab caste in 2 separate sequences. For the double caste bottom slab, it is necessary introduce counter measures such as pre-cooling prior to the site construction. Also, another crack preventive measure is to lower the initial casting temperature by $25^{\circ}C$ or less to satisfy 1.2 through crack index criterion. In the $1^{st}$ and $2^{nd}$ caste bottom slab, the surface crack index was over 1.2. Therefore, the surface cracks can be controlled by implementing the curing conditions proposed in this study. Since the side wall's surface crack index was over 1.0, it is safe to assume that the counter preventive measures can control width and number of cracks.

• Journal of Korean Tunnelling and Underground Space Association
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• v.11 no.1
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• pp.11-22
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• 2009

Tunnel excavation with several sections and appropriate auxiliary measures such as face bolt and pre-grouting are widely used in case of weak and less rigid ground for the stability of a tunnel face during excavation. This papers first described the evaluation methods proposed in technical literature to maintain the tunnel face stable, and then studied by FEM analysis whether face reinforcement is need in what degree of ground deformation and strength features for the stability of a tunnel face when excavating by full excavation with sub-bench. Lastly, a three dimensional FEM analysis was performed to study how the tunnel face itself and the ground around the tunnel behave depending on different bolt layouts, length of bolts, number of bolts. There were relative differences in comparison of results on the stability of a tunnel face by a theoretical evaluation methods and FEM analysis, but the same in reinforced effect of face. It was found that the stability of a tunnel face can be obtained with face bolt installed longer than 1.0D (tunnel width), bolt density of about 1 bolt per every $1.5\;m^2$ (layout of grid type), and reinforcement area of $120^{\circ}$ arch area of upper section.

• 한국방재학회:학술대회논문집
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• 2007.02a
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• pp.335-339
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• 2007

A jointed plain concrete pavement(JPCP) slab was tested in Incheon International Airport construction work to study the early-age property of JPCP slab. The temperature and moisture data of the concrete slab had been collected and analyzed. The setting time of the concrete was decided by using the maturity method. The initial setting time is 2 hours 40 minutes after the placement of the slab. The investigation and analysis of the slab began from the initial setting time. The strains of different locations and different depths of the slab show different variation character.

• Proceedings of the Korea Concrete Institute Conference
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• 2000.10b
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• pp.1169-1174
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• 2000

Since the cement-water reaction in exothermic by nature, the temperature rise within a large concrete mass. Significant tensile stresses may develop from the volume change associated with the increase and decrease of the temperature with the mass concrete. There thermal stresses will cause temperature-related cracking in mass concrete structure. These typical type of mass concrete include mat foundation, bridge piers, thick wall, box type walls, tunnel linings, etc. Crack control methods can be considered at such stages as designing, selecting the materials, and detailing the construction method. Temperature and analysis was performed by taking into consideration of the cement type and content, boundary and environment conditions including the variations of atmospheric temperature and wind velocity. This is paper, the effect of separate placement of thermal crack control footing was analysed by a three dimensional finite element method. As a result, using this method, thermal crack control can be easily performed for structures such as mat structures.