• Proceedings of the Korean Institute of Building Construction Conference
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• 2014.11a
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• pp.178-179
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• 2014

The fine blast furnace slag is widely used as the admixture as it helps to increase the fluidity, long term strength of the concrete but decrease the heat of hydration. In case of the fine blast furnace slag, if the fineness of the slag is enhanced with the addition of gypsum to the concrete for the supplement of low strength in early stage and the facilitation of the initial hydration, the quality of the concrete is expected to change depending on the volume of the gypsum volume fraction. But, up to now the study on the fine blast furnace slag has only focused on the effect of fineness, replacement and admixture and there have been almost no studies on the effect of the gypsum volume fraction. Accordingly, this study focuses on what effect the gypsum volume fraction would make on the fluidity characteristics of the ultrafine furnace slag cement paste by using the rheology properties.

• International Journal of Railway
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• v.7 no.1
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• pp.8-15
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• 2014

Recently, in the total railroad construction field, concrete slab tracks have been adapted in place of ballast tracks. Because ballast tracks need frequent maintenance and are difficult to handle due to increasing maintenance costs, eventually concrete slab tracks were selected as an alternative. However, owing to the hydration heat reactions and temperature-affected shrinkage of the concrete, a variety of studies to solve maintenance problems related to concrete slab tracks are underway. This study analyzed characteristics of TQI values evaluating track irregularity, investigated the relationship between crack progress and TQI, and then evaluated the correlation between the two values. Through our analysis, we found that there is a need to supplement the problems of the current method and develop a track evaluation index which takes cracking into account. We also concluded that TQI is the main decision-making tool in track maintenance.

• Proceedings of the Korea Concrete Institute Conference
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• 1999.04a
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• pp.209-214
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• 1999

Strength provisions in Korea Concrete Institute code are more conservative that those in ACI code by increasing load factors and decreasing capacity reduction factors. Cement content of mix design in construction field is usually higher than the modified for standard deviation because of rigorous inspection. Higher cement content increases not only strengths but also heat of hydration, shrinkage and brittleness which are not beneficial. To reduce and optimize the cement content in current mix design of Korean Highway Corporation, properties of fresh and hardened concrete for 16 different mix proportions have been investigated. It is found that the chemical admixture and cement of current mix proportions for highway construction are somewhat higher than the optimum amount. Therefore, the optimum mix design for 16 different purposes has been proposed.

• Proceedings of the Korea Concrete Institute Conference
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• 2001.05a
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• pp.521-526
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• 2001

Box-culvert is very important structure used almost every road construction. However this is treated very simple structure in design and construction. So many crack such as nonstructural crack has been occurred. This crack is very harmful on durability of concrete. In this study, thermal crack, one of the nonstructural crack, of box-culvert controled by using rapid-strength belite cement concrete. In this process, not only heat of hydration and thermal stress but also material mechanics properties and characteristics of durability were tested. and same model box-culvert using OPC concrete is constructed in same condition for comparison.

• Proceedings of the Korea Concrete Institute Conference
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• 1998.10b
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• pp.928-933
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• 1998

The temperature and stress behaviour of mass concrete pier at early ages was analysed based on the finite element method. The pier investigated is a three-dimensional structure of which the cross-sectional shape varies from a circle to an ellipsoid along the longitudinal axis. In order to obtain the transient temperature and stress distributions in the structure, a three dimensional method was adopted, because the structure of this type cannot be modeled accurately by a two-dimensional method. Temperature analysis was performed by taking into consideration of the cement type and content, boundary and environment conditions including the variations of atmospheric temperature and wind velocity. The results of this study may be useful for the temperature control to restrain thermal cracking and the construction management to design the resonable curing method of mass concrete structure.

• Proceedings of the Korea Concrete Institute Conference
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• 2010.05a
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• pp.291-292
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• 2010

In this study, high-strength concrete mixtures were made with blast-furnace slag of 50% and 70% replacement level to evaluate material properties including compressive strength development, adiabatic temperature rise, autogenous shrinkage and chloride-ion migration coefficient. Test results showed that the use of high percentage blast-furnace slag in high-strength concrete can reduce heat of hydration and chloride-ion migration coefficient, result in control thermal cracking and improve durability performance especially under high corrosive environment.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2020.06a
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• pp.90-91
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• 2020

As the construction site has become narrower recently, the importance of mass concrete is naturally being highlighted as skyscrapers become popular. However, it is not possible to install the entire volume per day if the mass concrete is installed due to the Remicon 8⦁5 system and the 52-hour workweek system. When the mass concrete base is divided into several days, cold joints occur because the consolidation of joints is not integrated due to different degree of hardening in the case of the previous layer and the next day. As a result, existing research has shown that if super retarding agent are mixed into Ready Mixed Concrete (hereinafter referred to as Remicon) using sugar as a raw material to delay the curing time of concrete, cold joints are inhibited and cracks are inhibited by reducing the initial hydration heat.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.629-632
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• 2008

As concrete is a material which is subject to wide quality fluctuations by temperature, grip of seasonal feature and maintenance of ambient temperature and humidity to secure the quality required after casting concrete are able to keep away from harmful effects. In case of summer, a high temperature has caused rapid hydration reaction of cement in early age, which has caused to decrease strength by autogenous shrinkage. Therefore we need to consider a countermeasure for decrease in the hydration heat of hot-weather concrete, according to minimize water and cement content and use mineral admixtures In this experimental research, the compressive strength development for replacement ratio of mineral admixtures, curing temperature and methods of concrete was investigated to confirm the effects of mixture design and curing condition on compressive strength of concrete.

• 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.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.19 no.1 s.71
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• pp.15-25
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• 2006

The researches on the early-aged concrete hydration process and the techniques for the early-aged concrete crack control mainly have been focused and developed on the massive concretes in both experimental and numerical studies. However, those researches for relatively thin members such as the upper slab of the reinforced concrete rahmen bridge have nearly been attempted. In this study, a designing technique for crack controlling in the thin members of the early-aged reinforced concrete rahmen bridges based on measured temperature history, strength revelation model and sinkage model is proposed. A method of calculating the reinforcing bar area for crack controlling is also proposed and it is found that the distributing bars under the design loads become the main reinforcing bars in the temperature stress analysis of the early-aged reinforced concrete rahmen bridges. It is shown that the proposed analysis technique is able to use the design of crack control for the early-aged reinforced concrete rahmen bridge.