• Proceedings of the Korean Institute of Building Construction Conference
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• 2002.05a
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• pp.21-26
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• 2002

This paper is intended to verify the efficiency of anti-freeze agent and insulating form by analyzing the temperature history and the property of strength-increase about the concrete that is placed in the insulating form and normal form, using new type anti-freeze agent in batcher plant According to the results about the temperature history, while the lowest temperature shows 3$^{\circ}C$ in case of normal concrete + euroform, 4$^{\circ}C$ in case of normal concrete + insulating form, it shows 6$^{\circ}C$ in anti-freeze agent + the insulating form, so the effect is most favorable. The compressive strength with mixing anti-freeze agent or not, shows high in order of standard curing, structure-managing and open air-placed specimen and the concrete mixing anti-freeze agent shows the highest compressive strength-increase.

• Proceedings of the Korea Concrete Institute Conference
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• 2003.05a
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• pp.95-100
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• 2003

The shrinkage of high strength/high performance concrete is very important property for the good working of a structure since it very often generates early age cracking due to thermal and autogenous shrinkage. Autogenous shrinkage occurs as a result of internal moisture depletion due to hydration and temperature-induced effects. The level of autogenous shrinkage occurring due to hydration also depends on temperature history at very early age. It is necessary that effect of temperature on autogenous shrinkage is investigated since the stress generated due to autogenous shrinkage is quantified. In this study, Effect of hydration heat evolution on autogenous shrinkage of high strength concretes with W/C=25-40% was investigated.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2013.05a
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• pp.334-336
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• 2013

In this study, the temperature history was evaluated for the improved bubble sheets combining hot wires and PE films, which were developed under the extreme environmental condition of -10℃ and applied on the top surface of slab to prevent initial damage by freezing. Results can be summarized as follows. If improved bubble sheets combining hot wires with different capacity on double and quadruple bubble sheets are used, the temperature history for all materials decreased to 2~3℃ below zero but all test materials except Type 1 secured the accumulative temperature of 45° D·D at 7 days of material age, required for the prevention of initial freezing damage. This indicates the bubble sheets can prevent the initial damage by freezing.

• KCI Concrete Journal
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• v.14 no.2
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• pp.81-85
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• 2002

The strength development of concrete is influenced by temperature and cement type which greatly affect hydration degree of cement. There is not pertinent concrete strength management method in korea. There are several methods for estimating the in-place strength of concrete. One such method is the maturity concept. The maturity concept is based on the fact that concrete gains strength gradually as a result of chemical reactions between cement and water; and for a specific concrete mixture, strength at any age and at normal conditions is related to the degree of hydration. The rate of hydration and, therefore, strength development of a given concrete will be a function of its temperature. Thus, strength of concrete depends on its time-temperature history. The goals of the present study are to investigate a relationship between strength of high-strength concrete and maturity that is expressed as a function of an integral of the curing period and temperature and predict strength of concrete.

• Journal of the Korea Concrete Institute
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• v.21 no.4
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• pp.481-488
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• 2009

It has been reported that the magnitude and the development rate of autogenous shrinkage of cement paste, mortar and concrete were affected by history and magnitude of inner temperature at an early age. But it was not enough to explain the relation between hydration heat and autogenous shrinkage at an early age, because there was no certain analysis on histories of hydration heat and autogenous shrinkage in previous studies. In our prior study, to understand the relationship between hydration heat and autogenous shrinkage of concrete at an early age, the analysis method for histories of hydration heat and autogenous shrinkage was suggested. Based on this method, early age properties of hydration heat and autogenous shrinkage of high strength concrete with different sizes and hydration retardation were investigated in this study. As a result of the study, properties of hydration temperature and autogenous shrinkage were different according to specimen size and hydration retardation. However, there was a close relationship between hydration temperature and autogenous shrinkage at an early age, especially between HHV and ASV as linear slopes of the sections where hydration temperature and autogenous shrinkage increase rapidly; the higher HHV, the higher ASV and the greater ultimate autogenous shrinkage. And it was found that, among the setting time, bend point and temperature increasing point, they were close relationship each other on cement hydration process.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2016.05a
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• pp.107-108
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• 2016

When the construction in a low temperature, the concrete performance is deteriorated by frost damage at early age. In this study, the form utilizing heating sheet and insulation is measured the performance to prevent frost damage at 10 below zero. It produced five types of the form and to measure the temperature history and compressive strength. At first, form attached heating sheet showed the highest temperature. But the form attached vacuum insulation showed the highest temperature ever since 12hours. In the case of compressive strength, the form attached heating sheet + isopink(polystyrene foam board) showed the highest compressive strength. It was followed by vacuum insulation. As a result, the form utilizing insulation and heating sheet helped to prevent frost damage.

• Proceedings of the Korea Concrete Institute Conference
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• 2004.05a
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• pp.128-131
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• 2004

This paper is to investigate the mock up test results of mass concrete for transfer girder using setting time difference with super retarding agent(SRA) to reduce hydration heat. According to test results, the temperature history of plain concrete without placing lift had a steep rising curvature, and plain concrete had a big temperature difference between surface and middle section of mass concrete, which may result in occurrence of temperature crack. However, considering placing method B, because setting time of middle section concrete was retarded with an increase in SRA contents, higher hydration heat temperature was observed at surface section concrete compared with that at middle section concrete at early age, which can lower the possibility of hydration heat crack. In case of placing method C, although peak temperature of hydration heat was much lower, at early age, high crack occurrence possibility of the hydration heat attributable to the big temperature difference between middle section and bottom section of concrete was expected at bottom section concrete. Therefore, the structure above the ground like transfer girder is not applicable to consider the placing method C.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.781-784
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• 2008

In this paper, insulating effect and strength development of concrete under low temperature are reported varying curing sheets. According to test results, in temperature -5$^{\circ}$C concrete subject to exposure and air cap condition, result in a frost damage at early age by a fall of below zero temperature. Mean while, the combination of PE film and non-woven fabric maintained around 3 $^{\circ}$C within first 24 hours since placement. For double bubble sheets, concrete temperature maintained above 7$^{\circ}$C due to its excellent heat insulating capability. As a result of core strength test, strength of specimens cured with viny + non-woven fabric and double bubble sheets had higher strength than strength of other specimens due to good heat insulation effect at early age.

• Computers and Concrete
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• v.20 no.5
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• pp.529-537
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• 2017

Excessively elevated temperature can lead to cracks in prestressed concrete (PC) continuous bridge with box girder on the pier top at cement hydration age. This paper presents a case study for evaluating the behavior of PC box girder during the early hydration age using a two-stage computational model, in the form of computer program ANSYS, namely, 3-D temperature evaluation and determination of mechanical response in PC box girders. A numerical model considering time-dependent wind speed and ambient temperature in ANSYS for tracing the thermal and mechanical response of box girder is developed. The predicted results were compared to show good agreement with the measured data from the PC box girder of the Zhaoshi Bridge in China. Then, based on the validated numerical model three parameters were incorporated to analyze the evolution of the temperature and stress within box girder caused by cement hydration heat. The results of case study indicate that the wind speed can change the degradation history of temperature and stress and reduce peak value of them. The initial casting temperature of concrete is the most significant parameter which controls cracking of PC box girder on pier top at cement hydration age. Increasing the curing temperature is detrimental to prevent cracking.

• Journal of the Korea Institute of Building Construction
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• v.13 no.6
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• pp.513-521
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• 2013

This study aimed to examine whether heat curing methods of concrete subjected to $-10^{\circ}C$ could be effective by varying the combination of heating cable and surface heat insulations. Three different concrete specimens incorporating 30% fly ash with 50% W/B were fabricated to simulate wall, column and slab members with dimensions of $1600{\times}800{\times}200$ mm for slab, $800{\times}600{\times}200$ mm for wall and $800{\times}800{\times}800$ mm for column. For heat curing combinations, Type-1 specimens applied PE film for slab, plywood for wall and column curing. Type-2 specimens applied double layer bubble sheet (2LB) and heating coil for slab, and 50 mm styrofoam for wall and column curing. Type-3 specimen applied 2LB for slab, electrical heating mat for wall and column inside heating enclosure. The test results revealed that the temperature of Type 1 specimen dropped below $0^{\circ}C$ beginning at 48 hours after placement due to its poor heat insulating capability. Type 2 and 3 specimens maintained a temperature of around $5{\sim}10^{\circ}C$ after placement due to favorable heat insulating and thermal resistance.