• Proceedings of the Korea Concrete Institute Conference
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• 2005.11a
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• pp.351-354
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• 2005

Quality of concrete required to achieve the desired levels of strength and durability depend on the effectiveness of the curing method. During cold weather, the concrete at the time of placement should be taken to prevent damage to concrete due to freezing. Since the cement-water reaction is exothermic by nature, the temperature within mass concrete can be quite high. The temperature control for massive sections should be taken more careful than for shallow sections. However, in the constructing hydraulic structures, the curing temperature control for concrete had been very difficult to be taken in a proper way because the conditions constructing them are poor and contractors are small enterprises. For several. reasons including above, Rural Research Institute has developed a device and program for recording curing temperature history in cold weather concrete and mass. As there are two major advantages of the device, namely cheapness and availability, this program and device has been recommended to the use of curing temperature control in cold weather concrete and mass.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.13 no.1
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• pp.419-424
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• 2012

This study is a research on the buckling analysis of a portable prestressing device using finite element analysis program, ABAQUS. In order to produce 50m-span PSC girders using pretensioning method, a portable prestressing device has to endure a large jacking force about 10MN. Therefore it shall be safe and stable about the jacking force. In this study, the buckling analysis technique is developed and the buckling analysis of a portable prestressing device is performed using previous studies about the analytical model that the validity of the analytical model was demonstrated by comparing analytical results with experimental results. The stability of the device to produce 10m span PSC girders is investigated.

• Proceedings of the Korea Water Resources Association Conference
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• 2017.05a
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• pp.276-276
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• 2017

홍수 시 하천의 급격한 유량증가로 인하여 하상의 변화를 야기할 수 있으며, 이를 저감하기 위한 하천사업에는 자연친환경적이고 고유속흐름에서도 변동되지 않는 하상재료를 도입한 연구들이 다양하게 진행되고 있으며, 과거 제방보호 기능만을 가진 단순한 호안에서 식생을 이용한 다양한 종류의 호안공법이 개발되어 각종 하천에 도입되고 있다. 호안공법을 도입할 때 고유속흐름과 식생의 유무에 따라 하천의 흐름에 미치는 영향을 파악하는 것은 하천설계에 있어 중요한 부분이다. 최근에는 기후변화로 인한 극우강우가 많아지고 호안의 안정성을 위한 평가기법이 제시되지 않기 때문에 호안사면의 수리학적 안정성과 지반공학적 파괴거동의 적절한 평가가 필요하다. 따라서 본 연구에서는 식생 유무에 따라 유속, 레이놀즈수, 바닥전단응력 등을 산정하여 흐름특성을 파악하고 호안 및 제방에 대한 적용성을 검토하고자 실험연구를 진행하였다. 실험에 사용된 재료는 모래, 식생점토. 본 연구를 위해 자체적으로 양생시킨 잔디를 이용하였으며, 실내 고속수로 실험 장치를 이용하여 유속의 변화에 따라 실험을 실시하였다. 이를 통해 초기상태의 재료와 세굴 이후의 세굴심을 비교하여 고유속흐름에서의 식생 유무에 따른 하상재료 유실변화 정도를 비교하고자 하였다.

• Journal of the Korean Society of Hazard Mitigation
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• v.11 no.2
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• pp.67-73
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• 2011

This study aims to develop an economical precast hollow concrete column with high constructability which consists of only splice sleeve and general reinforcing bar without using PC tendons in order to reduce the construction period and cost. With this purpose, this study performed the finite element analysis and tension test by using some variables such as length of sleeve, diameter of rebar and curing method for suggesting a grouting type splice sleeve which is a new type joint rebar and developing an optimized splice sleeve. As a result, the analysis on the tension performance of splice sleeve did not show any destruction caused by pull-out in reinforcing bar but it only occurred destruction of tension bar or bolt shear rupture from the mechanical defect of sleeve. Therefore, the experiment showed high performance in tension of the suggested splice sleeve and verified the application of precast hollow concrete column.

• The Journal of Engineering Geology
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• v.27 no.3
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• pp.233-244
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• 2017

We conducted hydraulic fracturing experiments on cement samples to investigate the dependency of fracture propagation on the viscosity of injection fluid and the in situ stress state. Ten cubic samples (20 cm side length) were produced using cement that was cured in water for more than one month. Samples were placed in a tri-axial compression apparatus with three independent principal stresses. An injection hole was drilled and the sample was hydraulically fractured under a constant injection rate. We measured injection pressures and acoustic emissions (AE) during the experiments, and investigated the fracture patterns produced by hydraulic fracturing. Breakdown pressures increased exponentially with increasing viscosity of the injection fluid. Fracture patterns were dependent on differential stress (i.e., the difference between the major and minor principal stresses). At low differential stress, multiple fractures oriented sub-parallel to the major principal stress axis propagated from the injection hole, and in some samples the fracture orientation changed during propagation. However, at high differential stress, a single fracture propagated parallel to the major principal stress axis. AE results show similar patterns. At low differential stress, AE source locations were more widespread than at high differential stress, consistent with the fracture pattern results. Our study suggests that hydraulic fracturing during shale gas extraction should be performed parallel to the orientation of minimum differential stress.

• 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.

• Proceedings of the Korea Water Resources Association Conference
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• 2018.05a
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• pp.480-480
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• 2018

전 세계적으로 자연 친화, 하천생태계 보전, 친수하천 등을 조성하기 위한 대대적인 하천 정비사업이 활발히 진행 중에 있다. 최근 홍수로 인한 제방 붕괴에 대응하기 위한 제방의 안정화 및 개선을 위한 방법으로 기존의 시멘트와 같은 혼합물질을 사용하지 않고 환경 친화적이고 지속 가능한 대안에 대한 수요가 증가되고 있는 추세이며 현재 노후화 된 불안정 제방에 대한 보강대책을 수립해나가는 과정으로써 친환경 신소재를 활용하여 제방을 보호하는 연구가 수행되고 있다. 제방사면에 적용되는 신소재는 바이오폴리머를 활용한 재료로써 공동연구기관 카이스트에서 개발된 환경 친화적인 물질로 미생물에 의해 유도된 고인장 및 인체 무해성 등의 특성을 갖고 있으며 경제적 타당성인 측면에서 시멘트와 비교 분석 되어야 하고 실제 현장에서의 적용 가능성, 신뢰성 및 내구성 검토 등 성능을 보장하기 위한 지속적인 연구가 필요한 상황이다. 이에 본 안동하천실험센터에서는 중규모 제방을 직접 제작하여 수리모형실험을 통한 친환경 신소재 활용 제방의 안정성 및 성능 평가를 실시하였다. 수리실험 조건은 카이스트에서 제시된 레시피를 기반으로 먼저 분말형태의 바이이폴리머를 물과 희석하여 만들어진 바이오폴리머 용액을 흙과 혼합한 뒤 제방표면에 직접 미장작업을 수행하여 실험조건에 따라 일정한 두께(1cm, 3cm, 5cm)로 피복하였다. 이후 월류 붕괴 실험이 가능한 3 - 5일 정도의 양생기간을 거쳐 실험을 진행하였다. 실험결과는 다수의 고프로(GoPro) 및 비디오 카메라 등 다양한 영상장치를 이용하여 픽셀기반의 영상분석기법을 활용한 시간 흐름에 따른 제방 사면에서의 붕괴규모를 산정하여 신소재의 피복 두께에 따른 제체의 붕괴 거동 및 안정성을 평가하였으며, 또한 제방 파괴부에서의 흐름 상황 및 유속이 붕괴 발달에 미치는 영향을 분석하기 위하여 PIV 분석을 실시하였다. 이번 연구의 최종목표는 지속적인 예비실험을 수행하여 월류 및 침투, 파이핑 등 파괴 인자 별 신소재의 성능 개선 및 개발된 새로운 공법에 대한 효과 검토를 통한 최적안을 도출함으로써 향후 실규모 실험실증을 통한 신소재 시공 및 공법에 대한 현장적용 가능성 검증을 거쳐 최종적으로 신소재 제방 공법 설계 기술, 신소재 및 공법 표준안, 제방공법 안정성 평가 가이드라인 등을 제시하고자 하며, 이러한 실험데이터를 축적함으로써 실제 제방 붕괴 시 비상대처계획 수립에 필요한 기초자료로 활용이 가능할 것으로 사료된다.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.41 no.6
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• pp.737-744
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• 2021

Spray paving minimizes material lost during the construction or repair of a road surface, and it can be done in conjunction with tack coating. This approach involves applying the asphalt mixture at the same time as spraying the tack coat by attaching a spraying device to the asphalt paver. When applying an asphalt overlay to an aged concrete surface, it is important to ensure the adhesion performance between different material properties. Accordingly, there is a need for a tack coat that can be applied by spray paving and that exhibits good adhesive performance on different materials. In this study, bonding strength tests under various conditions were performed to evaluate the basic performance of a tack coat developed for use with a spray paver. The bonding performance of the tack coat was observed to be affected by curing conditions and material lost during construction. The test results also showed that the tensile and shear bonding strengths of the developed tack coat were 1.21 and 1.99 times higher than those of a conventional one, respectively. As a result, the developed tack coat is considered suitable for application to spray paving.

• Journal of Korean Tunnelling and Underground Space Association
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• v.12 no.1
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• pp.75-85
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• 2010

The focus of this study is to evaluate the field applicability of the newly developed inorganic thixotropic-grout in various ways. In order to do this, the volume stability and the permeability of the inorganic thixotropic-grout have been measured and compared to the existing silica type grouts. In addition, the filling capability of the grout into the tail void has been evaluated through both an experiment with a miniature tail-void filling equipment and a test filling at the shield TBM construction site. The volume loss of the inorganic thixotropic-grout after a 14 day-curing under the atmosphere condition was appeared to be minimal. The excellent waterproofing ability of the inorganic thixotropic-grout was confirmed through a permeability test. The toxicity of the inorganic thixotropic-grout has been evaluated through a toxicity test of aquatic fishes (KS M 0111) and the pH value of the liquid eluviated from inorganic thixotropic-grout was measured as an average of 8.0 and a fatality rate of goldfish after 96 hours was 10% or so. The existence of harmful heavy metals in the liquid eluviated from the inorganic thixotropic-grout has been also examined through an atomic absorption spectroscopy (AAS) test. Any of harmful heavy metals were not detected and the detected level of $Cr^{6+}$ and Cd was far below the standard. Based on both an experiment with a miniature tail-void filling equipment and a test filling at the shield TBM construction site, the filling ability of inorganic thixotropic-grout into the tail void was proved to be excellent.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.31 no.3A
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• pp.235-249
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• 2011

A new form of I-type PSC bridge girder, which has hole in the web, is proposed in this paper. Three different concepts were combined and implemented in the design. First of all, a girder was precast at a manufacturing plant as divided pieces and assembled at the construction site using post-tensioning method, and the construction period at the site will be reduced dramatically. In this way, the quality of concrete can be assured at the manufacturing factory and concrete curing can be well controlled, and the spliced girder segments can be moved to the construction site without a transportation problem. Secondly, a numerous number of holes was made in the web of the girder. This reduces the self-weight of the girder. But more important thing related to the holes is that about half of the total anchorages can be moved from the girder ends into individual holes. The magnitude of negative moment developed at girder ends will be reduced. Also, since the longitudinal compressive stresses are reduced at ends, thick end diaphragm is not necessary. Thirdly, Prestressing force was introduced into the member through multiple stages. This concept of multi-stage prestressing method overcomes the prestressing force limit restrained by the allowable stresses at each loading stage, and maximizes the magnitude of applicable prestressing force. It makes the girder longer and shallower. Two 50 meter long full scale girders were fabricated and tested. One of them was non-spliced, or monolithic girder, made as one piece from the beginning, and the other one was assembled using post-tensioning method from five pieces of segments. It was found from the result that monolithic and spliced girder show similar load-deflection relationships and crack patterns. Girders satisfied specific girder design specification in flexural strength, deflection, and live load deflection control limit. Both spliced and monolithic holed web post-tensioned girders can be used to achieve span lengths of more than 50m with the girder height of 2 m.