• Nuclear Engineering and Technology
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• v.45 no.3
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• pp.393-400
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• 2013

Concrete undergoing early frost damage in cold weather will experience significant loss of not only strength, but also of permeability and durability. Accordingly, concrete codes like ACI-306R prescribe a minimum compressive strength and duration of curing to prevent frost damage at an early age and secure the quality of concrete. Such minimum compressive strength and duration of curing are mostly defined based on the strength development of concrete. However, concrete subjected to frost damage at early age may not show a consistent relationship between its strength and durability. Especially, since durability of concrete is of utmost importance in nuclear power plant structures, this relationship should be imperatively clarified. Therefore, this study verifies the feasibility of the minimum compressive strength specified in the codes like ACI-306R by evaluating the strength development and the durability preventing the frost damage of early age concrete for nuclear power plant. The results indicate that the value of 5 MPa specified by the concrete standards like ACI-306R as the minimum compressive strength to prevent the early frost damage is reasonable in terms of the strength development, but seems to be inappropriate in the viewpoint of the resistance to chloride ion penetration and freeze-thaw. Consequently, it is recommended to propose a minimum compressive strength preventing early frost damage in terms of not only the strength development, but also in terms of the durability to secure the quality of concrete for nuclear power plants in cold climates.

• Journal of the Korea Concrete Institute
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• v.12 no.3
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• pp.47-55
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• 2000

Protections from the frost damage at early ages are one of the serious problems to be considered in cold weather concreting. Frost damage at early ages brings about the harmful influences on the concrete structures such as surface cracks and declination of strength development. Therefore, in this paper, protecting periods of frost damage at early ages according to the standard specifications provided in KCI(Korean Concrete Institute) are suggested by appling logistic curve, which evaluates the strength development of concrete with maturity. W/B, kinds of cement and curing temperatures are selected as test parameters. According to the results, the estimation of strength development by logistic curve has a good agreement between calculated values and measured values. As W/B and compressive strength for protecting from frost damages at early ages increase, it is prolonged. It shows that the protecting periods of FAC(Fly Ash Cement) and BSC(Blast-furnace Slag Cement) concrete are longer than those of OPC(Ordinary Portland Cement) concrete. The protecting peridos from frost damage at early age by JASS are somewhat shorter than those by this paper.

• Journal of the Korea Concrete Institute
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• v.19 no.1
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• pp.27-37
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• 2007

The purpose of this study is to propose a method to predict the minimum curing time of early age concrete required to prevent frost damage. Tests were performed to examine major factors, which affect the compressive strength of concrete frozen at early ages and investigate the source of frost damage at early age concrete. The results from the tests showed that the loss rate of compressive strength decreases as the beginning time of frost damage was delayed and water-cement ratio was lower. In addition, the test results also showed that concrete made with type III cement was less susceptible to frost damage than concrete made with ordinary Portland cement and frost damage occurred through the formation of ice lenses. When early age concrete is being damaged by frozen, a phase transition into ice of free water presented at the capillary pores of the concrete gives a reason for the decrease of compressive strength. Accordingly, the frost resistance of fresh concrete can be determined based on the saturation degree of the capillary pores. The method to predict the minimum curing time was suggested using the concept of critical saturation degree of the capillary pores.

• Proceedings of the Korea Concrete Institute Conference
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• 2001.11a
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• pp.629-634
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• 2001

Recently, to consider financial and constructive aspect, usage of Admixture, like Blast-Furnace Slag and Fly-Ash, are increased. Also the use of cold-weather-concrete is increased. Blast-furnace Slag, a by-product of steel industry, have many advantage, to reduce the heat of hydration, increase in ultimate strength and etc. But it also reduces early-age strength, so it is prevented from using of Blast-Furnace Slag at cold-weather-concrete. In this study, for the purpose of increasing usage of Blast-Furnace Slag at cold-weather-concrete, it is investigated the strength properties of concrete subjected to frost damage for the cause of early age curing. According to this study, if early curing is carried out before having frost damage, the strength of concrete, subjected to frost damage, is recovered. And that properties is not connected with the frost cause.

• Proceedings of the Korea Concrete Institute Conference
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• 2002.05a
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• pp.143-148
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• 2002

Recently, to consider economical and constructive aspect, Usage of Admixture, like Blast-Furnace Slag and Fly-Ash, are increased. Blast-Furnace Slag, a by-product of steel industry, have many advantage, to reduce the heat of hydration, increase in ultimate strength and etc. But it also reduces early-age strength, it is prevented from using of Blast-Furnace Slag at cold-weather-concrete. In this study, for the purpose of increasing usage of Blast-Furnace Slag at cold-weather-concrete, it is investigated the strength properties of concrete subjected to time and period of frost damage for early age curing. According to this study, if early age curing is carried out before having frost damage, the strength of concrete, subjected to frost damage, is recovered. And that properties is not connected with the frost cause.

• Nuclear Engineering and Technology
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• v.44 no.5
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• pp.523-534
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• 2012

The objective of this study was to experimentally investigate the effect of heat curing methods on the temperature history and strength development of slab concrete exposed to $-10^{\circ}C$. The goal was to determine proper heat curing methods for the protection of nuclear power plant structures against early-age frost damage under adverse (cold) conditions. Two types of methods were studied: heat insulation alone and in combination with a heating cable. For heat curing with heat insulation alone, either sawdust or a double layer bubble sheet (2-BS) was applied. For curing with a combination of heat insulation and a heating cable, an embedded heating cable was used with either a sawdust cover, a 2-BS cover, or a quadruple layer bubble sheet (4-BS) cover. Seven different slab specimens with dimensions of $1200{\times}600{\times}200$ mm and a design strength of 27 MPa were fabricated and cured at $-10^{\circ}C$ for 7 d. The application of sawdust and 2-BS allowed the concrete temperature to fall below $0^{\circ}C$ within 40 h after exposure to $-10^{\circ}C$, and then, the temperature dropped to $-10^{\circ}C$ and remained there for 7 d owing to insufficient thermal resistance. However, the combination of a heating cable plus sawdust or 2-BS maintained the concrete temperature around $5^{\circ}C$ for 7 d. Moreover, the combination of the heating cable and 4-BS maintained the concrete temperature around $10^{\circ}C$ for 7 d. This was due to the continuous heat supply from the heating cable and the prevention of heat loss by the 4-BS. For maturity development, which is an index of early-age frost damage, the application of heat insulation materials alone did not allow the concrete to meet the minimum maturity required to protect against early-age frost damage after 7 d, owing to poor thermal resistance. However, the combination of the heating cable and the heat insulating materials allowed the concrete to attain the minimum maturity level after just 3 d. In the case of strength development, the heat insulation materials alone were insufficient to achieve the minimum 7-d strength required to prevent early-age frost damage. However, the combination of a heating cable and heat insulating materials met both the minimum 7-d strength and the 28-d design strength owing to the heat supply and thermal resistance. Therefore, it is believed that by combining a heating cable and 4-BS, concrete exposed to $-10^{\circ}C$ can be effectively protected from early-age frost damage and can attain the required 28-d compressive strength.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2019.05a
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• pp.197-198
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• 2019

The aim of the research is evaluating the feasibility of inspection for early age frozen damage and for expansion of concrete under the various time periods of -20℃ temperature condition. When the concrete samples were exposed for 12 hours and 24 hours, the frozen depth of the concrete were 10 and 60 mm, respectively, under the wet conditions. From the experiment results of temperature and expansion, only surface area suffered frozen damage for 12 hours exposing conditions while entire area suffered frozen damage for 24 hours exposing conditions.

• Journal of the Korea Concrete Institute
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• v.15 no.1
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• pp.43-51
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• 2003

Recently, to consider financial and constructive aspect usage of Admixture such as Blast-Furnace Slag and Fly-Ash, are increased. Also the use of cold-weather-concrete is increased. Blast-Furnace Slag, a by-product of steel industry, have many advantage to reduce the heat of hydration, increase in ultimate strength and etc. But it also reduces early-age strength, so it is prevented from using of Blast-Furnace Slag at cold-weather-concrete. In this study, for the purpose of increasing usage of Blast-Furnace Slag at cold-weather-concrete, it is investigated the strength properties of concrete subjected to frost damage for the cause of early age curing. The factors of this experience to give early frost damaged were Freezing temperature(-1, -10, $-15^{\circ}C$), Early curing age(0, 12, 24, 48hour), Freezing times(0, 12, 24, 48hour). According to this study, if early curing is carried out before haying frost damage, the strength of concrete used admixture, subjected to frost damage, is recovered. And that properties are considered, the effect of using admixture like blast-furnace-slag, is very high

• Proceedings of the Korean Institute of Building Construction Conference
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• 2016.10a
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• pp.150-151
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• 2016

In previous study, researchers studied development of early anti-freezing cement at low temperature (-5℃) using hydration characteristics of reduction slag. In this study, the durability of concrete using reduction slag was conducted. The experiment result, reduction slag makes high temperature and improves compressive strength due to quick setting. And then result of durability show that it is no problem. However, it is considered that further study is needed about high shrinkages which was indicated in dry shrinkage.

• Journal of Industrial Technology
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• v.25 no.A
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• pp.49-56
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• 2005

Recently, very-early strength latex-modified concrete(below ; VES-LMC) has been developed for repairing and overlaying the old concrete bridge deck. VES-LMC provides the advantage of very-early-strength, as well as high flexural strength, bond strength, durability, resistance to corrosion, reduced water permeability and resistance to damage from freeze-thaw cycles. The compressive and flexural strength of VES-LMC are 21 MPa and 4.5 MPa at 3 hours after concrete placing, respectively. However, VES-LMC would have a relatively large shrinkage at early-age because of reduced water-cement ratio, big water self-dissipation, and rapid hydration reaction. Therefore, the purpose of this study was to evaluate the early-age and restrained shrinkage of VES-LMC, having an experimental variables such as latex contents and cement types. The latex contents included 0%, 5%, 10%, 15% and 20%, and the cement types included ordinary portland cement and very-early strength cement.