• Journal of the Korea Concrete Institute
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• v.19 no.1
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• pp.47-56
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• 2007

Recently, tunnels are increasingly constructed in this country with the increased construction of highways, high-speed railways and subways. Shotcrete is one of the major processes in the tunnel construction. Many problems, however, exist in the current shotcrete practice. The purpose of the study is, therefore, to explore the trobles in the current shotcreting practice, and to develop high-quality silica fume shotcrete. For the purpose of security a long-term durability of shotcrete, this study conducted combined deterioration tests. In this study, a combined deterioration test in consideration of a variety of deterioration factors were proceeded. Especially, micro-silica fume that was used frequently in overseas because of a outstanding strength-promotion effect was applied to combined deterioration test, and a long-term durability of shotcrete was investigated according to additions mixing. As a result of test, the shotcrete mixed Micro-silica fume showed a good deterioration quality compared with the other mixes. And is shows that the Micro-silica fume has an outstanding strength-promotion effect and is effective to secure a long-term durability of shotcrete by means of decreasing a deterioration caused by steel fiber mixed.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.34 no.1
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• pp.73-85
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• 2014

The CFT (Concrete Filled steel Tubes) column-footing connection is cast-in-place embedded type which provides simple construction procedure, low cost, and superior structural performance. In this study, CFT column-footing connection of modular pier is proposed and structural performance is evaluated by experimental tests. To evaluate structural performance of the CFT column-footing connection, a series of experimental tests were performed for the 4 specimens with different embedded depth. As a result of the quasi-static test, the specimen with 0.6D (0.6 times the outside diameter of steel tube) embedded depth showed relatively low ductility than other specimens with larger embedded depth due to cone failure of base concrete occurred during the lower loading step. On the contrary, cone failure of the base concrete was not observed in the specimens with larger embedded depth than 0.9D, but typical flexural failure in lower part of CFT column was observed. With the analyses of force-displacement curve, displacement ductility, and energy dissipation capacity, it is concluded that the rational range of embedded depth of the CFT column-footing connection is from 0.9D to 1.2D in view of good seismic performance.

• Tunnel and Underground Space
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• v.17 no.4
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• pp.266-284
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• 2007

Recently, many efforts have been made to construct the first unlined tunnel, without in-situ concrete lining, in Korea. However, the lack of reliability in the performance of shotcrete as permanent tunnel support prevented from its realization. Shotcrete has been regarded to have significant problems in field application and long term performance because of unsatisfactory strength level and durability compared to those of European countries. In this study, the high strength shotcrete satisfying compressive strength over 40 MPa and flexural strength over 4.5 MPa was developed from optimized mix design. The type of accelerators and the amount of silica fume were selected as the main factors in mixing process and the analyses were carried out up to the elapsed time of 2 years. In order to evaluate the short term durability of shotcrete, an array of laboratory test consisting of freeze-thaw, carbonation chloride penetration and permeability test was performed. For long-term durability tests, specimens have been put in an operated highway tunnel to expose them to the similar environment when they are actually used as an unlined tunnel support. From the strength and durability tests, it was found that only alkali-free based accelerator satisfied the target strength of this study and also, the developed shotcrete showed very high performance in its durability.

• Proceedings of the Korea Water Resources Association Conference
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• 2005.05b
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• pp.879-883
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• 2005

우리나라는 하천유역의 도시화 추세 속에 불투수층의 증가로 빗물의 일시 유출로 인한 홍수발생으로 많은 인명과 재산피해가 발생하고 있어 방재적 차원에서의 수자원관리가 시급한 실정이다. 또한, 초기 빗물과 합류식 하수도의 월류수에 의한 하천, 호소, 및 습지의 수질오염문제도 많이 발생하고 있다. 이러한 문제를 해결하기 위하여 콘크리트로 제작된 PC 지하식 빗물저류시설로서 상부의 공간은 공원, 운동장, 주차장 등 다양하게 이용하면서 방재와 치수를 가능케 할 수 있다. 또한, PC 콘크리트 빗물저류조는 현장 타설이 아닌 PC콘크리트 블록을 현장에서 조립하여 시공기간이 대폭적으로 단축되고, 작업환경 및 주변환경을 개선시킬 수 있다. 또한, 지하수의 보전, 회복을 위한 빗물저류 침투 시설 역할도 수행하여 비상용수를 확보하고 여름철 홍수 시 빗물을 가두어 재해를 방지하는 등의 다목적 시설로 활용된다. 지하 매립형 빗물저류조는 기존의 암거설계기준을 참조하여 일본의 내진설계 기준을 반영하였으며, 고강도 콘크리트를 사용하여 강도 또한 뛰어나다. 그리고 시공이 간편하고 공기의 단축에 탁월한 효과를 나타내며, 빗물저류조 설치는 다음과 같은 특징이 있다. 1. 지하저류형 빗물저류조 시설로 설계되어 토지의 효과적인 이용이 기대된다. 2. 공사기간이 짧아 경제적이다. 3. 안정된 구조체이다. 4. 부지의 형태에 맞춘 시공이 가능하다. 5. 소규모에서 대규모의 유수지까지 광범위하게 대응이 가능하다. 6. 방재역할 수행 및 빗물이용의 역할을 담당할 수 있다. 7. 불투수층이 증가하고 있는 도시지역에서 적극 활용가능하다.로 판단된다.한 예비방류의 시행과 강우종료 후에도 이수용량에는 손실이 없는 저수지의 관리방안의 지침이 되는데 효율적이라 판단되었다. 방법을 개발하여 개선시킬 필요성이 있다.>$4.3\%$로 가장 근접한 결과를 나타내었으며, 총 유출량에서도 각각 $7.8\%,\;13.2\%$의 오차율을 가지는 것으로 분석되어 타 모형에 비해 실유량과의 차가 가장 적은 것으로 모의되었다. 향후 도시유출을 모의하는 데 가장 근사한 유출량을 산정할 수 있는 근거가 될 것이며, 도시재해 저감대책을 수립하는데 기여할 수 있을 것이라 판단된다.로 판단되는 대안들을 제시하는 예비타당성(Prefeasibility) 계획을 수립하였다. 이렇게 제시된 계획은 향후 과학적인 분석(세부평가방법)을 통해 대안을 평가하고 구체적인 타당성(feasibility) 계획을 수립하는데 토대가 될 것이다.{0.11R(mm)}(r^2=0.69)$로 나타났다. 이는 토양의 투수특성에 따라 강우량 증가에 비례하여 점증하는 침투수와 구분되는 현상이었다. 경사와 토양이 같은 조건에서 나지의 경우 역시 $Ro_{B10}(mm)=20.3e^{0.08R(mm)(r^2=0.84)$로 지수적으로 증가하는 경향을 나타내었다. 유거수량은 토성별로 양토를 1.0으로 기준할 때 사양토가 0.86으로 가장 작았고, 식양토 1.09, 식토 1.15로 평가되어 침투수에 비해 토성별 차이가 크게 나타났다. 이는 토성이 세립질일 수록 유거수의 저항이 작기 때문으로 생각된다. 경사에 따라서는 경사도가 증가할수록 증가하였으며

• Journal of the Korea Concrete Institute
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• v.28 no.5
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• pp.545-553
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• 2016

This paper presents experimental static test results of the precast concrete panels developed for short-span concrete bridge deck form. Different from LB-DECK, concrete rib attached to the bottom surface of concrete panel, and Top-bar is not used at the top surface of concrete panel. Number of concrete ribs and cross-section details of concrete rib are determined from the analytical results of parametric study considering the span length and the thickness of concrete bridge decks. Shear rebars are installed at the top surface of concrete panel for composite action between precast concrete panel and cast-in-place concrete. In order to evaluate the safety and the serviceability of the developed short-span concrete panel subjected to design load, static load test is conducted. Three test panels with span length of 1.6m are fabricated, and during the load test displacements, strains and cracks of test panels are measured and final failure modes are investigated. Serviceability of the test panels is evaluated based on the results of displacements, cracking load, and crack width at the design load level. Safety is also evaluated based on the comparison of the ultimate strength and the factored design load of test panels. Based on the test results, it is confirmed the short-span precast concrete panel satisfies the serviceability and safety regulated in design codes. In addition, the range of span length of concrete bridge decks for the short-span concrete panel is discussed.

• 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 the Korea Academia-Industrial cooperation Society
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• v.19 no.3
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• pp.542-552
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• 2018

In this paper, the precast method of a concrete eco-pillar debris barrier was proposed to improve the construct ability and economic efficiency. The performance was validated by experimental and structural analysis. The steel debris barrier has a high construction cost and causes environmental damage with corrosion. The construction of a concrete eco-pillar debris barrier has been increased recently. On the other hand, there are no design standards regarding debris barriers in Korea, and debris barriers are being designed by the experience and sense of engineers. Therefore, in this study, a method to determine the design external forces was proposed and the design was performed by applying a hollow cross-section to the debris barrier. In addition, three types of connection methods of a concrete cantilever column with the maximum bending moment acts were proposed, and validation of the performance of each type was performed with a real-scale experiment. The experimental results showed that the type with loop reinforcement had the highest rigidity and the type with anchorage performance exceeded the maximum bending moment according to the ultimate load. In the manufacturing procedure of mock-up debris barriers, the type with an anchorage-bar was found to have superior construct ability.

• Journal of Korean Society of Steel Construction
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• v.20 no.2
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• pp.227-236
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• 2008

The kind of concrete generally used in steel concrete composite bridges is normal-weight concrete whose unit weight is ${2,300kg/m^{3}}$. However, using lightweight concrete in composite bridges diminishes the sectional forces due to the self-weight of concrete decks. As a result, this will make the bridge design more economical. The type of concrete deck that could be adopted in composite bridges using lightweight con crete may be classified into Cast-In-Place (C.I.P.) concrete deck and precast concrete deck. These two types of decks have some differences with respect to structural behavior and constructional method, and hence,structural behavior of stud shear connectors that connect a concrete deck to a steel girder is changed with the type of deck used. In this study, push-out tests were conducted to evaluate the characteristics of static behavior of the stud shear connectors with a precast deck using lightweight concrete. Also, additional precast deck specimens with bedding layer that had shear keys and devices for transverse confinement of the bedding layer for the prevention of cracks occurring in the bedding layer were tested. These cracks The efficiency of these devices was then evaluated.

• Journal of the Korea Institute of Building Construction
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• v.10 no.5
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• pp.113-119
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• 2010

Fire resistance and field tests for high-strength concrete(HSC) of 80MPa were carried out to evaluate whether or not it shows the same material properties even in the field condition of being mass-produced and supplied. As a result, it was found that fire resistant HSCs containing composite fiber(NY, PP) of 0.075% have great resistance to fire and spalling. In the field test, before the pumping air contents, slump flow, U-box, L-flow, compressive strength, gap of hydration temperature of interior and exterior of specimen and placing ratio per hour satisfied the required properties of HSC. However, after the pumping of HSC, as slump flow and L-flow were slightly less than required criterion, they need to be improved. In terms of hydration temperature of HSC, it was found to satisfy the related criterion. Packing ability as well as placing ratio per hour of HSC, which was about $44m^3$, show outstanding results. If slump flow of developed ternary HSC is improved after the pumping it can be useful for the construction of high-rise buildings.

• Journal of the Korea institute for structural maintenance and inspection
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• v.19 no.3
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• pp.92-103
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• 2015

Development of new concrete bridge deck system with FRP plank using as a permanent formwork and the main tensile reinforcement recently has been actively conducted. Concurrent use as a reinforcing material and a permanent formwork, it is possible to reduce the construction time and construction costs than the usual concrete slab. In this study, an experiment was carried out for the bond stress between cast-in-place concrete and the type of FRP plank using as a permanent formwork. The interfacial fracture energy that can be one of the most important parameters were evaluated for adhesion performance and bond stress to know the characteristics of the failure mechanism of the adhesion surface. Interfacial fracture energy of normal concrete is 0.24kN/m of GF11 case, in the case of GF21, 0.43kN/m appears, in the case of CF11 and GF31, 0.44kN/m and 0.46kN/m respectively it appeared. In case of RFCON, 0.52kN/m appears from GF12, the CF12 and GF22, 0.51kN/m and 0.36kN/m appeared each case.