• International Journal of Concrete Structures and Materials
• /
• v.2 no.2
• /
• pp.115-122
• /
• 2008

Ductility is important in the design of reinforced concrete structures. In seismic design of reinforced concrete members, it is necessary to allow for relatively large ductility so that the seismic energy is absorbed to avoid shear failure or significant degradation of strength even after yielding of reinforcing steels in the concrete member occurs. Therefore, prediction of the ductility should be as accurate as possible. The principal aim of this paper is to present the basic data for the ductility evaluation of reinforced high-strength concrete beams. Accordingly, 23 flexural tests were conducted on full-scale structural concrete beam specimens having concrete compressive strength of 40, 60, and 70MPa. The test results were then reviewed in terms of flexural capacity and ductility. The effect of concrete compressive strength, web reinforcement ratio, tension steel ratio, and shear span to beam depth ratio on ductility were investigated experimentally.

• International Journal of Concrete Structures and Materials
• /
• v.8 no.4
• /
• pp.269-278
• /
• 2014

When concrete is being transported through a pipe, the lubrication layer is formed at the interface between concrete and the pipe wall and is the major factor facilitating concrete pumping. A possible mechanism that illustrates to the formation of the layer is the shear-induced particle migration and determining the rheological parameters is a paramount factor to simulate the concrete flow in pipe. In this study, numerical simulations considering various rheological models in the shear-induced particle migration were conducted and compared with 170 m full-scale pumping tests. It was found that the multimodal viscosity model representing concrete as a three-phase suspension consisting of cement paste, sand and gravel can accurately simulate the lubrication layer. Moreover, considering the particle shape effects of concrete constituents with increased intrinsic viscosity can more exactly predict the pipe flow of pumped concrete.

• Proceedings of the Korean Institute of Building Construction Conference
• /
• 2017.05a
• /
• pp.276-277
• /
• 2017

Deicing agent affect concrete durability such as scaling, rebar corrosion strength of concrete. In this study, developed deicing agent satisfied with EL610 is evaluated to compare affects to concrete with no deicing agent and chloride-containing deicing agents. Deicing agents are applied to concrete surface during four months twice a week. Chloride content, chloride penetration depth and concrete strength are evaluated. After experiment, chloride content, chloride penetration depth of concrete are as follows. Chloride-containing deicing > Eco friendly deicer > No deicing agents. Concrete strength are also as follows. Chloride-containing deicing > Eco friendly deicer > No deicing agents. From experiment, developed deicing agent shows low chloride content in concrete and affect concrete strength little lower than chloride-containing deicing.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2005.05b
• /
• pp.393-396
• /
• 2005

This paper presents the results of drying shrinkage of concrete using shrinkage-reducingadmixture(DSRA) studied by the authors through mock-up test. DSRA is proportioned by expansive admixture and shrinkage reducing agent(SRA). Flowing concrete method is also applied to assist the concrete to reduce drying shrinkage by decreasing water content at the same time. The use of EA and SRA does not affect fluidity, bleeding and setting time. Compressive strength of concrete using EA along with SRA exhibited less than that of plain concrete. However, The compressive strength with combination of EA-SRA along with flowing concrete method shows comparable to that of plain concrete. The application of developed method can contribute to reducing drying shrinkage by as much as 30-40$\%$ compared with that of plain concrete.

• Korean Journal of Childcare and Education
• /
• v.15 no.1
• /
• pp.37-55
• /
• 2019

Objective: This study investigated whether executive function has a significant relationship to concrete, picture, and language clue tasks of the arithmetic story problem-solving ability, and its effects. Methods: The participants in the study were 112 young children at childcare centers. The following methods were used to evaluate executive function: Day-Night/Flag-Raising tasks, DCCS tasks, and digit span-reverse digit span methods. To measure the arithmetic story problem-solving ability concrete, picture, and language clue tasks were evaluated. Results: First, the higher the child's age, the higher their executive function and arithmetic story problem-solving abilities were. Second, there is a significant positive correlation between a young child's executive function and arithmetic story problem-solving ability. Third, when the task presentation method varied for concrete, picture, and language clue tasks, the effect of the subordinate factor of the execution function of the arithmetic story problem-solving ability also varied. Conclusion/Implications: Analysis confirmed the relationship between young children's executive function and arithmetic story problem-solving ability. The results are meaningful in showing that the sub-factors of the executive function have different influences on concrete, picture, and language clue tasks of the arithmetic story problem-solving ability.

• Steel and Composite Structures
• /
• v.39 no.3
• /
• pp.307-318
• /
• 2021

Utilizing fibers is an effective way to avoid the brittle behavior of the conventional concrete and can enhance its ductility. In particular, propylene fibers can improve concrete properties, including energy absorption, physical and mechanical properties, controlling shrinkage cracks. The increase of fiber density leads to an increase of the overlapping surface of the fiber of concrete and, in turn, a decrease of cracks developed in the concrete. However, the workability of fiber reinforced concrete tends to be lower than the conventional concrete owing mainly to the hairline thickness and excessive concentration of fibers. The low slump of concrete impedes the construction of reinforced concrete members. In this research, we study if the utilization of magnetic water can alleviate the workability issue of young fiber reinforced concrete. To this end, the compressive and flexural strength of four types of concrete (conventional concrete, fiber reinforced concrete, magnetic concrete, magnetic fiber-reinforced concrete) is studied and compared at three different ages of 7, 14, and 28 days. In order to study the influence of the fiber density and length, a study on specimens with three different fiber density (1, 2, 5 kg of fiber in each cubic meter of concrete) and fiber length (6, 12, 18 mm) is undertaken. The result shows the magnetic fiber concrete can result in an increase of the flexural and compressive strength of concrete at higher ages.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2005.11a
• /
• pp.587-590
• /
• 2005

This study investigates the efficient construction scheme of the immersed tunnel focusing on the hydration heat. In this respect, some alternatives in curing, temperature condition and removing of the forms are compared together to meet the required criteria. It is addressed that the strict construction stage analysis considering the placing scheme of concrete is one of the key factors to trace the realistic structural behavior for the hydration heat.

• Proceedings of the Korean Institute of Building Construction Conference
• /
• 2005.05a
• /
• pp.41-44
• /
• 2005

The aim of this study is to develop experimentally ultra high-strength concrete with compressive strength over 100MPa with current materials by important factors to influence the compressive strength of concrete. There are so many factors which influence the manufacturing of ultra high-strength concrete. But the experimental factors selected in this study are the sand aggregate ratio, the silica fume replacement ratio, the type of aggregate. the type of superplasticizer, the fiber mixing ratio. The results of this experimental study show that. it is possible to applicate in the field

• Proceedings of the Korea Concrete Institute Conference
• /
• 2004.05a
• /
• pp.624-627
• /
• 2004

Most concrete is recently made of an aggregate which is properly absorbed, and carried in it according to its capability at every fields. We have been close to demand new capability of high flowing and enduring for specific concretes. That is difficult to cope with claiming the efficiency on deterioration from lack of a high Quality aggregate. Therefore, For solving the problems we apply to method of packaged dry combined materials for concrete using dried materials. That is to say that it is a kind of making into an instant. In this study, There is a purpose to present fundamental data, comparing and analyzing a phenomenon of aggregate's absorption following the rate of adding water, for using existing materials.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2006.05a
• /
• pp.54-57
• /
• 2006

The purpose of this study is to estimate the shear strength of high-strength SFRC beam by the comparison of normal-strength SFRC beam. To achieve the goal of this study, 9th specimens were made and tested. From the analyzing test result and previous researches, the shear strengthening effect of steel fiber in high-strength is evaluated as superior than normal-strength concrete. And the proposed shear strength equation of SFRC is underestimated the shear capacity of high-strength SFRC beam. Finally, the shear strengthening effect of steel fiber in high-strength concrete is evaluated about 3.5 times larger than normal-strength concrete.