• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.517-520
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• 2008

Gravity dam use self weight to stand external force like hydraulic pressure. In general, gravity dam concrete is divided into internal and external concrete. Seongdeok dam is gravity dam which is being constructed in Cheongsong-gun, Gyeonsangbuk-do. And upstream cofferdam was constructed to examine the temperature crack due to hydration heat and to decide the height of placement. In this study, we examined the mix design of internal/external concrete and physical properties(compressive strength, adiabatic temperature rise). And we also performed laboratory tests to verify exothermic properties. Lastly, we measured the hydration heat and thermal stress of upstream cofferdam.

• Asia-Pacific Journal of Business Venturing and Entrepreneurship
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• v.7 no.2
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• pp.101-111
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• 2012

In the ALC(Autoclaved lightweight concrete) manufacturing process, if the pre-cured semi-cake is removed after proper time is passed, it will be hard to retain the moisture and be easily cracked. Therefore, in this research, we took the research by multiple regression analysis to find relationship between variables for the prediction the hardness that is the control standard of the removal time. We study the relationship between Independent variables such as the V/T(Vibration Time), V/T movement, expansion height, curing time, placing temperature, Rising and C/S ratio and the Dependent variables, the hardness by multiple regression analysis. In this study, first, we calculated regression equation by the regression analysis, then we tried phased regression analysis, best subset regression analysis and residual analysis. At last, we could verify curing time, placing temperature, Rising and C/S ratio influence to the hardness by the estimated regression equation.

• Journal of Korean Society of Steel Construction
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• v.18 no.2
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• pp.191-201
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• 2006

New design equations for calculating the lateral-torsional buck ling moment resistances of stepped I-section beams with/without continuous lateral top-flange bracing subjected to a point load, a series of point loads, and a uniformly distributed load, are suggested based on the results of elastic finite-element analyses. The new equations presented in this study are compared with the current moment gradient modifiers presented by other researchers and specifications. Although the study paper presents mainly stepped-beam cases subjected to a point load and a uniformly distributed load. The proposed equations include the length-to-height ratio effects for stepped beams with continuous lateral top-flange bracing. The new moment gradient correction factors could be easily used to calculate the lateral-torsional buckling moment resistance of stepped I-beams.

• Journal of the Korea Concrete Institute
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• v.23 no.5
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• pp.657-665
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• 2011

LB-DECK, a precast concrete panel type, is a permanent concrete deck form used as a formwork for cast-in-place concrete pouring at bridge construction site. LB-DECK consists of 60 mm thick concrete slab and 125 mm height Lattice-girders partly embedded in the concrete slab. These decks have been applied to the bridges, which girder spacings are short enough to resist longitudinal cracking caused by construction loads. This paper presents experimental research work conducted to evaluate the cracking load of LB-DECKs designed for long span bridge decks. Twenty four non-composite beams and four composite beams are fabricated considering three design variables of thickness of concrete slab, height of lattice-girder, and diameter of top-bar. Static loads controlled by displacements are applied to test beams to obtain cracking and ultimate loads. Vertical displacements at the center of beams, strains of top-bar, crack propagation in concrete slab, and final failure modes are carefully monitored. The obtained cracking loads are compared to the analytical results obtained by elastic analyses. Long-term analyses using age-adjusted effective modulus method (AEMM) are also conducted to investigate the effects of concrete shrinkage on the cracking loads. Based on the test results, the tensile strength and the design details of LB-DECKs are discussed to prevent longitudinal cracking of long span bridge decks.

• Journal of the Korea institute for structural maintenance and inspection
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• v.27 no.5
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• pp.9-15
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• 2023

In this study, the lamination performance and strength characteristics of cement-based composite materials according to the laminated specimens manufacturing method were analyzed. As a result of evaluating the buildability according to the layer height, the highest dimensional stability was shown when the layer height was 10 mm in all parts. The mold casting specimen and the printing-Z specimen showed the same compressive strength performance at the age of 28 days. On the other hand, the compressive strength at 28 day of printing-X specimen was the lowest at 71.72 MPa, and 8% lower than that of the mold casting specimen and the printing-Z specimen. The split tensile strength of the laminated specimen may show similar performance to that of the mold casting specimen, but the strength performance may decrease by more than 10% depending on the direction of the layer and the number of layers in the specimen. As a result of the interface analysis of the laminated specimen through X-ray CT analysis, it was confirmed that pores of a certain size were distributed along the interface of the layer.

• Journal of the Korean Recycled Construction Resources Institute
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• v.5 no.1
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• pp.59-67
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• 2017

The objective of this paper is to investigate experimentally the effect of replacement of recycled coarse aggregates with 5~13mm in size on a field applicability of concretes through Mock-up test. Seven different mock-up specimens were prepared with the size of $1200{\times}800{\times}800mm$ simulating column and wall. For the concrete mixtures, 24MPa, 27MPa and 40MPa of nominal strength were adopted with 30% and 70%(only for 24MPa) of 5~13mm recycled coarse aggregate (RCA) replacement and without 5~13mm RCA(Plain). For test items, slump, slump flow, compressive strength with different curing conditions, core drilling, rebound numbers and drying shrinkage were measured. Test results indicated that 30% of 5~13 mm RCA replacement resulted in increase in slump, slump flow and resistance against segregation, while air contents decreased compared to those of plain mixture. Compressive strength of concrete with 30% of 5~13mm RCA was shown to be higher than that of plain mixture due to optimum packing effect associated with presence of well graded aggregates. Rebound number of the mock-up specimen with 30% of 5~13mm RCA had lower fluctuation according to hitting location than that of plain mock-up specimen. It is believed from the results of the study that replacement of 30% of 5~13mm RCA brings desirable improvement in various aspect of concrete performance due to associated dense packing effect.

• Journal of Korean Tunnelling and Underground Space Association
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• v.21 no.6
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• pp.811-823
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• 2019

Slip form method is applied to many cases of a shaft these days because it is safer, more economical and faster than cast-in-place method. Slip-up height of the method is approximately 2.5 to 4.0 m/day. If the temperature of concrete is outside the range of 10 to 30℃, the effects of changes in strength or elastic characteristics are significant. Therefore, it is difficult for slip-up speed to be higher than 3 m/day during winter construction. In addition, concrete has heat caused by hydration, which causes temperature cracking of hardened concrete. Therefore, temperature control of concrete curing is necessary for the continuous slip-up of slip form. In this study, the rebound hardness, time of ultrasonic waves propagation, heat of hydration, and external temperature are measured by developing heating panels and test devices for the continuous slip-up. Based on this, heating slip form is manufactured; this was applied to "Kimpo sites" and "Sinwol sites". The compared slip-up speed samples were 1.9 m/day or 0.200 m/hr on average at Gimpo sites (08:00~17:30) and 2.0 m/day or 0.210 m/hr at Sinwol sites.

• Journal of Korean Society of Steel Construction
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• v.24 no.3
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• pp.267-278
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• 2012

In general, the H-shaped steel ribs or triangular lattice girders have been mostly used in constructing tunnels through the NATM construction method. The H-shaped steel rib has higher flexural and axial strength than the triangular lattice girder, but many unexpected gaps can occur in the concrete lining system after shotcreting if the H-shaped steel rib is used as the support system. To achieve better shotcreting quality, the triangular lattice girder was developed. However, in general, the triangle lattice girder has low flexural and axial strength. Likewise, the triangular lattice girder, which has circular sectional members, has so many fractures from welded points at the joints between the members. Finally, the new type of tetragonal lattice girder was developed to overcome those problems. In this study, the structural performance of the tetragonal lattice girders was evaluated through analytical and experimental studies. In the analytical studies, the four-point bending analysis, the traditional evaluation method to determine the flexural strength of the lattice girder, was performed. Moreover, the linear-elastic analysis and stability analysis of the arch structure made by the lattice girders were performed to measure structural performance. Experiments were likewise performed to compare the structural performances of the tetragonal girder with traditional triangular lattice girders.

• Journal of the Korean Geosynthetics Society
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• v.15 no.2
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• pp.55-64
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• 2016

The construction of the road NATM tunnel, which undergoes the weathered zone of the mountain, was in process with the reinforcement methods such as the rock bolt, shotcrete depositing, and the multi step grout with large diameter steel pipe. The collapse from the ceiling, and on the ground surface area(sink hole), of which were measured to be 25m from the ground surface($V=12m(W){\times}14m(L){\times}5m(H)=840m^3$), as well as excessive displacements in the tunnel, had occurred. In order to execute the necessary reconstruction work, the causes of the surface collapses were inspected through the field investigation, in-situ tests, and numerical analysis. As a result, several proper solutions were suggested for both internal and external reinforcements for the tunnel. As a result of numerical analysis, the collapsed zone of the tunnel was reinforced up to 0.5D~1.0D laterally by the cement grouting on the ground surface, 0.5D longitudinally by the multi step grout with large diameter steel pipe in tunnel. With further reinforcement implemented by rebars in lining, the forward horizontal boring was executed to the rest of the tunnel to evaluate the overall status of the tunnel face. Appropriate reinforcement methods were provided if needed.

• Magazine of the Korea Concrete Institute
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• v.11 no.4
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• pp.61-67
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• 1999

물론 이 글이 콘크리트 분야에 종사하는 사람이 알아야 하는 모든 것을 언급하지는 않는다 ; 본인의 저서 'Properties of Concrest'의 판매에 나쁜 영향을 주고 싶지도 않다. 내가 원하는 것은 콘크리트를 제작할 때 우리 모두가 주의를 기울여야 하는 중요한 몇 가지를 강조하는 것이다. 포트랜드 시멘트만 들어있는 보통의 콘크리트가 사용되는 시대는 이미 사라져가고 있고, 단순한 응용을 제외하고는 곧 사라질 것이다. 대부분의 경우는 가능한 일련의 시멘트계 재료 중에 선택을 해야 한다. 혼화제, 특히 고성능 감수제는 중요한 역할을 한다. 물을 많이 첨가하는 것이 작업성을 높이는 유일한 방법도 아니고 최선의 방법도 아니다. 성능을 기준으로 한 기준설정에 관여하는 사람은 이 모든 것을 명심해야 한다. 그렇지 않으면 시방기준에 명시된 규정과 근원적인 요구사항이 잘못 이해되고, 시험배합을 통해서만 잘못되었다는 것이 분명해지게 된다. 그 단계에서는 예상보다, 비록 틀린 것이지만, 더 많은 비용이 들 것이다. 시방규정은 통상적인 조항 외에 갈수록 내구성에 관심을 더 많이 보인다. 가끔은 내구성이 구조물의 기대수명에 대한 연수로 표현되기도 한다. 이 숫자를 배합재료에 관한 자료로 변환시키는 데는 여러 배합재료 및 배합비가 콘크리트의 성질에 미치는 영향에 관하여 깊이 알고 있어야 한다. 모든 사람이 그러한 구체적인 지식을 가질 필요는 없지만, 각 조직마다 상의할 수 있는 사람은 있어야 한다. 엔지니어가 언급한 규정이 따로 없고, 도면의 주를 참고하거나 구체적인 절이 명시되지 않은 상태에서 국가 시방기준을 통해서 조금씩 내용을 수집해야 하는 경우의 상황은 더 난감하다. 이러한 경우는 배합설계나 재료의 선택을 책임지고 있는 사람이, 환경에 대한 노출조건 및 필요한 배합재료에 관하여 잘 알고 있어야 한다. 일반적으로 말해서 콘크리트의 배합은 필요한 특정용도에 따라서 선택되어야 한다. 이것이 사람들이 고성능 콘크리트라 부르는 것이라고도 할 수 있다. 내 생각으로는 고성능 콘크리트와 보통 콘크리트의 경계는 곧 사라질 것이고, 앞으로 대다수 고객에게 주문 콘크리트 혹은 맞춤 콘크리트를 제공해야 할 것이다. 만약 이러한 접근방식에 더 많은 비용이 든다면, 그것을 보상하는 방법은 콘크리트에 대한 이미지를 높이고, 또한 앞으로 모든 용도에 계속적으로 이용될 수 있도록 하는 것이다. 아니면 구조물을 보수하고, 보수한 것을 또 보수하고, 해체하고 해야 할 것이다. 결국은 재활용 골재를 생산할 수 있다고 웃으면서 말할지 모르지만, 이런 식으로는 불만을 지닌 사용자가 콘크리트를 가능하면 멀리하게 만들 것이다. 콘크리트는 절대 심각한 경쟁에 처하지 않을 것이라는 가정은 무모하다. 내가 배합비에 대해서 강조해 왔지만, 이것으로 최종적으로 좋은 콘크리트가 된다는 보장은 없다. 비빔에서는 일반적으로 큰 문제는 없지만 골재에 함유된 수분을 더 잘 제어해야하고 주의를 게을리하지 말아야 한다. 비빔시간은 모든 재료가 잘 섞이기에 충분해야 하는데, 마이크로 실리카가 포함되어 있을 경우에는 더욱 그렇다. 단위시간당 믹서의 작업량을 높이기 위해서 충분히 비비지 않아서는 안된다. 그리고 마지막으로, 콘크리트가 타설되고 다져진 후, 적절하게 양생이 되어야 한다. 마이크로 실리카가 배합에 사용되었을 경우에는 특히 그러하지만, 이것은 모든 콘크리트에서 양생을 잘하는 것이 피복부에서 유해물질이 유입되는 것을 최소화하고 철근을 완전히 보호하는데 있어서 절대적이다. 내가 지금까지 말한 것은 콘크리트에 관한 충분한 지식과 이해를 필요로 한다. 이것은 당연하고 또한 적절한 것이라고 생각한다. 왜냐하면 더 이상 콘크리트를 수준낮은 싸구려 재료로 간주해서는 안되기 때문이다.