• Journal of the Korean Recycled Construction Resources Institute
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• v.5 no.3
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• pp.223-229
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• 2017

When concrete is exposed to neutron rays for a long time, the concrete tends to become activated. If activated, it is classified as middle or low level radioactive waste. However, the great amount of the activated concrete is hard to dispose. In this study, low-activation cement was developed for decreasing the activated waste from shielding concrete around nuclear reactor. Furthermore, the manufactured low-activation was analyzed with activation nuclide Eu, Co. The low-activation cement showed great advantage for low-activation with detecting none of Eu and 3.75ppm of Co while ordinary portland cement showed 0.4~0.9ppm of Eu, 5.5~19.8ppm of Co content. As the results of physical properties of the low-activation cement, it is similar to type 1 ordinary portland cement and accords with type 4 low heat portland cement. Meanwhile, as for the chemical properties of the cement, it accords wite type 1 and 4 at the same time.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.637-640
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• 2008

Since the first underground LNG tank was constructed in Incheon, continuously many LNG tanks were constructed in Tongyoung and Pyongtaek. The storage capacity of LNG tank increased by 200,000kl and the structure size and the concrete mixing design has changed. The crack of concrete induced by the heat of hydration is a serious problem, particularly in massive concrete structures. In order to control the thermal crack of massive concrete, the low heat portland cement(type Ⅳ) is applied to bottom annular part, bottom central part, lower walls and ring beam. In this study, in order to thermal crack control about the LNG tank wall(lot 8 of #16 Pyongtaek LNG tank) in winter, analysed the concrete temperature, the extention of term, the curing condition and the concrete mixing design. When the concrete mixing design is changed from OPC+FA25% to LHC+FA25%, the thermal crack index is 1.33 and satisfied with construction specifications(over 1.2).

• Magazine of the Korea Concrete Institute
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• v.10 no.4
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• pp.195-204
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• 1998

Generally, in order to maintain high strength in concrete, it needs high cement content and low water-cement ratio.makes internal temperature rising after concrete placing inevitably, and happens temperature stress that makes initial cracks of concrete structure. Therefore, to control the thermal stress of high-strength concrete, we made 3 types of the fineness of ground granulated blast-furnace slag and 4 steps replacement. and then measured an amount of temperature rising and elapsed time of maximum temperature and strength of concrete. Also we considered the test results of heat evolution amount and heat evolution of cement paste made with 5 steps replacement by GGBF slag.As result of this study, in case of the 50% of replacement and the 6,000$\textrm{cm}^2$/g of fineness, we obtained satisfactory results that not only the controlled effect of temperature rising but strength at early ages.

• Journal of the Korea Concrete Institute
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• v.22 no.3
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• pp.389-397
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• 2010

Concrete has excellent mechanical properties, high durability, and economical advantages over other construction materials. Nevertheless, it is not an easy task to apply concrete to long span bridges. That's because concrete has a low strength to weight ratio. Ultra high performance concrete (UHPC) has a very high strength and hence it allows use of relatively small section for the same design load. Thus UHPC is a promising material to be utilized in the construction of long span bridges. However, there is a possibility of crack generation during the curing process due to the high binder ratio of UHPC and a consequent large amount of hydration heat. In this study, adiabatic temperature rise and mechanical properties were modeled for the stress analysis due to hydration heat. Adiabatic temperature rise curve of UHPC was modeled superposing 2-parameter model and S-shaped function, and the Arrhenius constant was determined using the concept of equivalent time. The results are verified by the mock-up test measuring the temperature development due to the hydration of UHPC. In addition, models for mechanical properties such as elastic modulus, tensile strength and compressive strength were developed based on the test results from conventional load test and ultrasonic pulse velocity measurement.

• Journal of the Korea Institute of Building Construction
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• v.16 no.5
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• pp.413-419
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• 2016

In the cold-weathering concrete construction, it is important to ensure stable strength development of concrete in a low temperature environment. In this study, Non-curing cement(NCC) using the classified high fineness cement and self-heating powder was investigated for stable strength development without curing in a low temperature environment (less than $0^{\circ}C$). The actual size Mock-Up tests by various cement type and curing condition are performed to evaluate the strength development and hydration heat of concrete.

• Magazine of the Korean Society of Agricultural Engineers
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• v.22 no.1
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• pp.53-66
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• 1980

The research work is concerned with the analytical and experimental studies on the heat transfer phenomenon around the underground concrete digester used for biogas production Systems. A mathematical and computational method was developed to estimate heat losses from underground cylindrical concrete digester used for biogas production systems. To test its feasibility and to evaluate thermal parameters of materials related, the method was applied to six physical model digesters. The cylindrical concrete digester was taken as a physical model, to which the model,atical model of heat balance can be applied. The mathematical model was transformed by means of finite element method and used to analyze temperature distribution with respect to several boundary conditions and design parameters. The design parameters of experimental digesters were selected as; three different sizes 40cm by 80cm, 80cm by 160cm and l00cm by 200cm in diameter and height; two different levels of insulation materials-plain concrete and vermiculite mixing in concrete; and two different types of installation-underground and half-exposed. In order to carry out a particular aim of this study, the liquid within the digester was substituted by water, and its temperature was controlled in five levels-35。 C, 30。 C, 25。 C, 20。C and 15。C; and the ambient air temperature and ground temperature were checked out of the system under natural winter climate conditions. The following results were drawn from the study. 1.The analytical method, by which the estimated values of temperature distribution around a cylindrical digester were obtained, was able to be generally accepted from the comparison of the estimated values with the measured. However, the difference between the estimated and measured temperature had a trend to be considerably increased when the ambient temperature was relatively low. This was mainly related variations of input parameters including the thermal conductivity of soil, applied to the numerical analysis. Consequently, the improvement of these input data for the simulated operation of the numerical analysis is expected as an approach to obtain better refined estimation. 2.The difference between estimated and measured heat losses was shown to have the similar trend to that of temperature distribution discussed above. 3.It was found that a map of isothermal lines drawn from the estimated temperature distribution was very useful for a general observation of the direction and rate of heat transfer within the boundary. From this analysis, it was interpreted that most of heat losses is passed through the triangular section bounded within 45 degrees toward the wall at the bottom edge of the digesten Therefore, any effective insulation should be considered within this region. 4.It was verified by experiment that heat loss per unit volume of liquid was reduced as the size of the digester became larger For instance, at the liquid temperature of 35˚ C, the heat loss per unit volume from the 0. 1m$^3$ digester was 1, 050 Kcal/hr m$^3$, while at for 1. 57m$^3$ digester was 150 Kcal/hr m$^3$. 5.In the light of insulation, the vermiculite concrete was consistently shown to be superior to the plain concrete. At the liquid temperature ranging from 15。 C to 350 C, the reduction of heat loss was ranged from 5% to 25% for the half-exposed digester, while from 10% to 28% for the fully underground digester. 6.In the comparison of heat loss between the half-exposed and underground digesters, the heat loss from the former was fr6m 1,6 to 2, 6 times as much as that from the latter. This leads to the evidence that the underground digester takes advantage of heat conservation during winter.

• Proceedings of the Korea Concrete Institute Conference
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• 2009.05a
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• pp.565-566
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• 2009

Supplementary cementing materials (SCM), such as silica fume, slag, and low-calcium fly ash, have been widely used as mineral admixtures in high strength and high performance concrete. Due to the chemical and physical effect of SCM on hydration, compared with Portland cement, hydration process of cement incorporating SCM is much more complex. This paper presents a numerical hydration model which is based on multi-component concept and can simulate hydration of cement incorporating SCM. The proposed model starts with mixture proportion of concrete and considers both chemical and physical effect of SCM on hydration. Using this proposed model, this paper predicts the following properties of hydrating cement-SCM blends as a function of hydration time: reaction ratio of SCM, calcium hydroxide content, heat evolution, porosity, chemically bound water and the development of the compressive strength of concrete. The prediction results agree well with experiment results.

• Proceedings of the Korea Concrete Institute Conference
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• 1997.10a
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• pp.293-298
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• 1997

Corrosion of steel reinforcing in concrete deteriorated by freezing/thawing and carbonation was characterized. Concrete specimens were prepared using various kinds of cements such as ordinary portland cement (type I), low heat portland cement (type IV, belite rich cement), sulphate resistance portland cement (type V), blast furnace slag portland cement and ternary blended cement. Of various cements, type V and type IV with lower $C_3A$ content revealed better steel corrosion resistance after freezing/thawing and carbonation. $C_3A$ content in cement might affect freezing/thawing resistance in sea water.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2022.11a
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• pp.115-116
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• 2022

Large concrete mass members are commonly used as matte bases for skyscrapers. In general, Integral casting is preferred to secure construction convenience and durability quality rather than separate casting. However, there is a possibility that cracks may occur in the early stages due to the generation of a lot of hydration heat, and thus durability will decrease, so it is necessary to determine an appropriate mixture and verify it through experiments. The purpose of the study was to conduct a review on the durability of the optimal high-performance low-heating concrete combination derived through the experiment and to conduct a review analysis on the performance satisfaction and performance expression mechanism.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2006.05a
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• pp.39-42
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• 2006

Recently, more highly effective construction materials are needed for the reasonable and economical structure system is required as the construction structures become more multi storied, large-sized and diversified. That is to say, the highly qualified concrete, the molt universal construction material is positively promoted as a part of plan to establish the effective space according to the dead load of structures and diminish of segment profile and to build up the economic structures. In particular, it is tendency of that the study for high strength concrete increases and construction example of reinforced concrete (RC) using the high strength concrete partially increases. However, the high strength concrete has the problems such high brittleness and low ductility. Specially, for the high strength concrete, it has different strength from normal concrete as the internal temperature goes up steadily due to high heat of hydration by the quantities of highly level of cement, so the concrete which is mixed with various scible materials is used. This study conducted a basic experiment to conclude an adequate selection of materials and to calculate an optimal mixing proportion of those materials to produce High-strength concrete. And also we conducted an experiment to find out basic properties of this concrete such as slump-flow, strength.