• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.981-984
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• 2008

The super tall building above 100 floors is required that each floor's height is more than 4 meters, and each core wall's thickness is more than 60cm. Therefore, for the successive accomplishment of super tall building, the full scale mock-up test was required. The test results are as follows; Real strength of core wall was satisfied with design strength at 28 days regardless of types of strength, and according to the consolidation effect, lower part's strength was a little higher than upper part's strength. Lateral force of HSC was evaluated with max. $4.5ton/m^2$, and hydration temperature of mock-up test was evaluated that maximun heat of central part revealed about $80^{\circ}C$ at 70MPa and $65^{\circ}C$ at 50MPa, and, the difference between inner and outter part revealed about $30^{\circ}C$ at 70MPa and $12^{\circ}C$ at 50MPa. Also, no crack by hydration temperature was not shown on the surface.

• Journal of Korean Society of Steel Construction
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• v.25 no.1
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• pp.71-80
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• 2013

Fire-resistant (FR) test data for a square concrete-filled steel tube (CFT) columns consisting of high-strength steel (fy>650MPa) and high strength concrete (fck>100MPa) under axial loads are insufficient. The FR behavior of square high-strength CFT members was investigated experimentally for two specimens having ${\Box}-400{\times}400{\times}15{\times}3,000mm$ with two axial load cases (5,000kN and 2,500kN). The results show that the FR performance of the high-strength CFT was rapidly decreased at earlier time (much earlier at high axial load) than expected due to high strength concrete spalling and cracks. In addition, a fiber element analysis (FEA) model was proposed and used to simulate the fiber behaviour of the columns. For steel and concrete, the mechanical and thermal properties recommended in EN 1994-1-2 are adopted. Test results were compared to those of numerical analyses considering a combination of temperature and axial compression. The numerical model can reasonably predict the time-axial deformation relationship.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.4
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• pp.400-413
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• 2016

The horizontal shear capacity when the flange of a steel girder is replaced with 80 MPa concrete is important for its structural safety. In this study, 6 specimens with different interface conditions were designed and fabricated based on the Limit State Design Code on Korean Highway Bridges and static tests were performed to measure the horizontal shear capacity. Not only the resistance factors of the stud shear connector, concrete and reinforcement, but also the surface conditions of the casing concrete and spacing of the horizontal shear reinforcements were used as the experimental variables. The experiments showed that the interfaces between the steel girder and the concrete flange have stronger joint performance than those between the concrete flange and deck slab. To ensure the composite action in the plastic zone, the conservative horizontal shear reinforcement is more important than the roughness in the concrete face.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.325-328
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• 2008

Recently increasing interest in high-rise building around the world for more than 100 floor, the trend is the increasing use of high-strength and high-flowable concrete so as of productivity improvements and cost savings to improve the performance of the early strength development. This study is to reach the optimal combination by reviewing the performance of high-rise building which is required. The results, lower the ratio of W/B was an increase in compressive strength and early strength in the use of admixture decreased in the combination of higher replacement ratio of admixture.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2014.05a
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• pp.274-275
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• 2014

As the increase amount of high rise building, equipments for high rise building have been extensively studied. However quality problems caused as the pumping of concrete including loss of flowalility, air content and increasing of the temperature. In this study, fundamental performances of the 80 MPa concrete before·after pumping has been tested. Results showed slump flow increased after pumping temperature of concrete also increased after pumping. Results also shown air content all satisfied the target range and compressive strength of concrete increased about 20 % after pumping, All the performances satisfied the standard for 80 MPa.

• Journal of the Korea institute for structural maintenance and inspection
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• v.24 no.6
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• pp.85-91
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• 2020

The necessity for ground reinforcement of structures has been increasing in South Korea because buildings have encountered constructional problems such as inclined structures and collapses caused by earthquakes or differential settlement of the foundations. With regard to a ground reinforcement method, an increasing number of high-strength concrete piles have been used based on their advantages, including a wide range of penetration depth and a high load-bearing capacity. However, problems such as the destruction of a pile head during on-site placement work can occur when the pile has insufficient strength. For this reason, the strength of such piles should be managed more thoroughly. Thus, this study analyzed the strength properties of high-strength concrete piles using blast furnace slag (BFS) powder as a cement replacement, which was generated as an industrial byproduct. The analysis results indicated that the compression strength of the concrete piles increased when 10% to 20% of the cement was replaced with ground granulated blast-furnace slag (GGBS). In addition, the compression strength of the concrete piles was calculated to be 80.6 MPa when 20% of the cement was replaced with GGBS, which was greater by 5% than that of an ordinary Portland cement (OPC) specimen.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2009.11a
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• pp.51-54
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• 2009

In this study, the fire resistance test was carried out with a parameter such as fiber(PP+NY) mixed ratio on high strength concrete with 80MPa, and the spalling resistance property was evaluated. Concrete material test was carried out with a parameter such as fiber(PP+NY) mixed ratio(0%, 0.05%, 0.1%, 0.2%) of high strength concrete with 80MPa. Although the flowability and the strength capacity were delicately decreased with a increase of fiber mixed ratio, they satisfied the target limits. As the spalling resistance property after the fire resistance test of 3 hours, the spalling was partly shown on the high strength concrete with fiber(PP+NY) mixed ratio of 0% but, wasn't shown on the high strength concrete with fiber(PP+NY) mixed ratio of 0.05% ~ 0.2%.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.5
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• pp.688-696
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• 2016

This paper evaluates the effect of hot weather conditions on the fresh concrete characteristics of 80-MPa high-strength concrete. The slump flow, packing ability, setting time, hydration heat, and compressive strength were evaluated under exterior temperatures of $20^{\circ}C$, $30^{\circ}C$, and $40^{\circ}C$. The slump flow, arrival speed of 500 mm, and their changes with the elapsed time were found to bring the occurrence of rapid slump loss forward by about 30 minutes when increasing the temperature by $10^{\circ}C$ from $20^{\circ}C$. The initial and final setting times of the concrete at $20^{\circ}C$ were 7 hours and 12 hours, which were reduced by 1 hour and 3 hours at $30^{\circ}C$ and by 2 hours and 5 hours at $40^{\circ}C$, respectively. The hydration heat characteristics at $20^{\circ}C$ and $30^{\circ}C$ were similar in terms of the highest temperature of the concrete casting depth and the time when the maximum temperature occurred. However, at $40^{\circ}C$, the maximum temperature occurred about 4 hours earlier, and the highest temperature per the concrete casting depth increased by about $12^{\circ}C$. Therefore, it is concluded that the characteristics can vary according to the exterior temperature. Thus, quality assurance should consider workability, temperature cracks due to hydration heat, the properties of strength development, and other characteristics.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2023.05a
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• pp.177-178
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• 2023

In this study, the mass production process was simulated using a 1m³ batcher plant to evaluate the application of high-strength fire resistance concrete. The strength ranges of concrete were set to 50, 60, 70, and 80 MPa, and each concrete mix proportions was selected through preliminary experiments in the laboratory. For the selected concrete mix proportions, after the mixer load value was stabilized in the batcher plant, the slump flow and air content of the fresh concrete were evaluated, and the compressive strength was evaluated up to 56 days. As a result of the experiment, both the slump flow and air content of the fresh concrete satisfied the target performance, and in the case of compressive strength, 50 and 60 MPa satisfied the target performance at 28 days and 70 and 80 MPa at 56 days.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.42 no.4
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• pp.449-455
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• 2022

Concrete is the most widely used construction material. The heavy self-weight of concrete may offer an advantage when developing high compressive strength and good dimensional stability. However, it is limited in the construction of super-long bridges or very high skyscrapers owing to the substantially increased self-weight of the structure. For developing lightweight concrete, various lightweight aggregates have typically been utilized. However, due to the porous characteristics of lightweight aggregates, the strength at the composite level is generally decreased. To overcome this intrinsic limitation, this study aims to develop a construction material that satisfies both lightweight and high strength requirements. The developed cementitious composite was manufactured based on a high volume usage of hollow glass microspheres in a matrix with a low water-to-cement ratio. Regardless of the tested hollow glass microspheres from among four different types, compressive strength outcomes of more than 60 MPa and 80 MPa with a density of 1.7 g/cm³ were experimentally confirmed under ambient and high-temperature curing, respectively.