• Journal of the Korea Institute of Building Construction
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• v.14 no.2
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• pp.118-126
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• 2014

The establishment of the technology for evaluating friction resistance and pipe pressure and the relation of the fluid characteristics and pumpability of concrete is essential for concrete pumping performance for the rapid construction of super-tall buildings. In this study, a quantitative evaluation of concrete fluid characteristics and surface friction resistance was performed, applying different concrete mix proportions and pumping conditions. To achieve this, we developed a temporary horizontal pumping evaluation system to measure pipe pressure and surface friction characteristics, and performed an experiment to investigate the relations between concrete rheology characteristics and friction resistance in pipe. The experiment found that in terms of the rheology characteristics, plastic viscosity was reduced remarkably after pumping. As well, high regression between the surface friction and pressure gradient was confirmed. This means that it is possible to evaluate the friction resistance between concrete and pipe by means of a pumping system that includes a frictional resistance testing pipe. In addition, high regression between the plastic viscosity of concrete after pumping and friction resistance coefficient was confirmed. Finally, it is considered that pumping pressure can be predicted using the friction resistance coefficient derived in this study, and it has high regression.

• Magazine of the Korea Concrete Institute
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• v.20 no.6
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• pp.28-35
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• 2008

The Burj Dubai Project will be the tallest structure ever built by man; when completed the tower will be more than 700 meter tall and more than 160 floors. While the early integration of aerodynamic shaping and wind engineering considerations played a major role in the architectural massing and design of this multi-use/residential tower, where mitigating and taming the dynamic wind effects was one of the most important design criteria, the material selection for the structural systems of the tower was also a major consideration and required detailed evaluation of the material technologies and skilled labor available in the market at the time Concrete was selected for its strength, stiffness, damping, redundancy, moldability, free fireproofing, speed of construction, and cost effectiveness. In addition, the design challenges of using concrete for the design of the structural system components will be addressed. The focus on this paper will also be on the early planning of the concrete works of the Burj Dubai Project.

• Journal of the Korean Society for Railway
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• v.14 no.2
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• pp.143-150
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• 2011

This paper presents a preliminary study for air-tightness evaluation of vacuum tube structures for super-speed tube railway systems. The formula for flow rate of the air caused by the pressure difference of the inside and outside of the tube structure is derived based on Darcy's law. A test is then performed to measure the air-permeability of concrete with various compressive strengths, the result of which is used for analytical simulation of the air intrusion for a tube structure with a preliminarily defined section. It has been shown that concrete with the compressive strength of at least more than 50MPa is recommended for effective operation and maintenance of the vacuum pump systems, as the air-permeability of concrete is inversely proportional to the exponent of its compressive strength.

• Proceedings of the KIEE Conference
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• 2015.07a
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• pp.1438-1439
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• 2015

수질정화를 위하여 여러 가지 방법이 연구되고 있다. 지금까지의 연구결과는 분수대고정 콘크리트 시공에 따른 유동적인 효과의 미흡과 1.2m이상의 높은곳에 위치함으로써 효율저하가 있었으나 본연구는 효율저하를 막고 수중펌프 흡입구와 분수노줄막힘을 방지하기 위하여 0.7m의 높이에 수질정화장치를 설치하고 임펠러 회전체를 개방함으로써 보다 높은 성능을 가진 수질 정화장치용 분수를 만들어 안전도를 증가 시켰다.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2008.11a
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• pp.187-191
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• 2008

It is necessary to develop a technology for effectively controling explosive spalling of high strength concrete caused increasing construction of high rise building and putting up the fireproof standard of high strength concrete by MLTM (Ministry of Land, Transport and Maritime Affairs). Accordingly, it was investigated basic properties such as slump, air content and compressive strength, and fire resistance properties of high strength concrete using polypropylene fiber for field application as a countermeasure for explosive spalling of concrete on fire in this study, As a test result, it was confirmed that PP fiber is available as fire resistance method of high strength concrete.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2007.11a
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• pp.1-4
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• 2007

Because reinforced concrete structures were being high more and more in recent year, concrete was being demanded high performance of high strength and high fluidity. But various characteristics must be confirmed besides guarantee of demand strength in ultra-high strength concrete. In ultra-high strength concrete, autogenous shrinkage and drying shrinkage grow big because of a low water cement ratio and much quantity of binder. So dangerousness of crack generation grow big in early ages. And ultra-high strength concrete is influenced by use materials more than ordinary strength concrete. In this study we were examined mix design, atuogenous shrinkage and pumpability of ultra-high strength concrete to apply on the ground.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2011.05a
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• pp.99-101
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• 2011

In order to have pumping technology for high speed construction of tall building, study for quantitative evaluation of flow characteristics and pumpability should be conducted. So, this study evaluate the characteristics among the inner pipe pressure, fresh concrete properties and separated mortar through the continuous pumping test. Then it consider of relations between rheological properties and pumpability. In the result of test, it found that there are high interrelationship between the rheological characteristics which represented plastic viscosity and pressure lose by pipe length.

• Journal of the Korea Institute of Building Construction
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• v.18 no.1
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• pp.17-24
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• 2018

The pullout test, a nondestructive testing(NDT), for pre-installed inserts is perhaps the most widely used technique to estimate the in-situ compressive strength of concrete. It measures the force needed to pullout a standardized metal insert embedded into concrete members. The pullout test was certified by the American Society for Testing and Materials(ASTM) and Canadian Standards Association(CSA) as a reliable method for determining the strength of concrete in concrete structures under construction. To easily estimate the strength of ultra-high-strength concrete, a simplified pullout tester, primarily composed of a standard 12mm bolt with a groove on the shaft as a break-off bolt, an insert nut, and a hydraulic oil pump without a load cell, was proposed. Four wall and two slab specimens were tested for two levels of concrete strength, 80MPa and 100MPa, using a simplified pullout tester with a load cell to verify the advantages of the pullout test and simplified pullout test. The compressive strength of concrete, pullout load, and the rupture of the break-off bolt were measured 11 times, day 1 to 7, 14, 21, 28, and 90. The correlation of the pullout load and the compressive strength of each specimen show a higher degree of reliability. Therefore, a simplified pullout test can be used to evaluate the in-place strength of ultra-high-strength concrete in structures. The prediction equation for the groove diameter of the break-off bolt(y) with the concrete strength(x) was proposed as y=0.0184x+5.4. The results described in this research confirm the simplified pullout's utility and potential for low cost, simplicity, and convenience.

• Journal of the Korean Society for Railway
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• v.17 no.3
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• pp.186-192
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• 2014

In this paper, a reliability analysis is performed where the pressure change inside a concrete tube is probabilistically estimated considering the uncertainties inherent in the material and the system discontinuity. A set of uncertain quantities related to the equivalent system air permeability and the atmospheric pressure, are defined as random variables with specific distribution. The pressure change inside a concrete tube is then probabilistically described using both analytical and simulation approaches. The reliability analysis confirms that the geometric configuration of a concrete tube needs to be changed from the initial configuration obtained from the deterministic analysis.

• Journal of the Korea Institute of Construction Safety
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• v.6 no.1
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• pp.12-18
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• 2024

High-rise, large-scale, and diversification of buildings are possible, and the reduction of concrete cross-sections reduces the weight of the structure, thereby increasing or decreasing the height of the floor, securing a large number of floors at the same height, securing a large effective space, and reducing the amount of materials, rebar, and concrete used for designating the foundation floor. In terms of site construction and quality, a low water binder ratio can reduce the occurrence of dry shrinkage and minimize bleeding on the concrete surface. It has the advantage of securing self-fulfilling properties by improving fluidity by using high-performance sensitizers, making it easier to construct the site, and shortening the mold removal period by expressing early strength of concrete. In particular, with the rapid development of concrete-related construction technology in recent years, the application of ultra-high-strength concrete with a design standard strength of 100 MPa or higher is expanding in high-rise buildings. However, although high-rise buildings with more than 120 stories have recently been ordered or scheduled in Korea, the research results of developing ultra-high-strength concrete with more than 130 MPa class considering field applicability and testing and evaluating the actual applicability in the field are insufficient. In this study, in order to confirm the applicability of ultra-high-strength concrete in the field, a preliminary experiment for the member of a reduced simulation was conducted to find the optimal mixing ratio studied through various indoor basic experiments. After that, 130 MPa-class ultra-high-strength concrete was produced in a ready-mixed concrete factory in a mock member similar to the life size, and the flow characteristics, strength characteristics, and hydration heat of concrete were experimentally studied through on-site pump pressing.