• KCI Concrete Journal
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• v.14 no.3
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• pp.93-101
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• 2002

The details of an approach to account for the factors that have been found to affect the ability and the probability to control cracking due to sawcutting in newly constructed concrete pavements are presented. Several factors such as material strength parameters, method and quality of curing, slab and subbase stiffness, and concrete shrinkage affect the probability of crack initiation. Others are relevant to concrete mixture characteristics that affect development of early aged stresses caused by shrinkage and thermally induced contraction. This paper presents the results of a probabilistic analysis of the factors that affect crack control using sawcut notches. Cost analyses on both conventional and early-entry sawcutting methods are shown to support the results of the probabilistic analysis. From both an operational and cost standpoint, it is evident for the environmental conditions considered that early-entry sawcut methodology holds a significant advantage over conventional methods.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2001.11a
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• pp.76-81
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• 2001

Recently, the structure is higher and larger, so that the application of high-strength concrete is increased, And as the development of construction skills, it is possible to place during the winter. Concrete work during winter is indispensible to shorten time of completion and cut costs. When concrete work during winter is placed, it has anxiety that concrete freeze at low temperature. As repetition of concrete's freezing cause reduction of durability, it is necessary for mixing to pay attention to air content and W/C ratios. Accordingly, in this study, we estimate the frost resistance by air content and W/C ratios, and development of strength after early-frost damage in the high-strength concrete during the cold weather. In this study, it could be confirmed that factors which were air content, W/C ratios and early curing period, affected on the frost resistance.

• Proceedings of the Korea Concrete Institute Conference
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• 2000.10a
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• pp.355-358
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• 2000

Nowadays, with high-storied and large-sized of structures, high-strength concrete is applied to the various kinds of concrete structure. Among of them, for reduction of completion time, high-strength concrete is applied to the high-storied tower, building which is constructed continuously by the slip-form method and it is expected to be on the increase. In this case, it is very important to grasp development of early-strength to apply the slip-form method. But the strength data prior 1 day is rare. Therefore, to apply slip-form method in field, this study aim is to present basic data for development of early-strength of high-strength concrete, through examining development of strength by different curing temperature, replacement of fly-ash.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.05b
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• pp.361-364
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• 2005

This study reports the properties of high early strength of concrete using PC admixture. To apply these data to construction site, we did the lab tests and mock-up test. The target of this study is to accomplish early strength of concrete(5 MPa/18 hr), and we tested by the different factors, such as the type of admixtures, curing temperature, the amount of binder, etc. Through the test of concrete using the different type of admixture, PC type was more excellent than PNS type admixture. According to these tests, we concluded that we can apply this type of PC Admixture to the civil & construction site, and we can reduce the term of works and finally we can accomplish the economical construction.

• Journal of the Korean Society of Tobacco Science
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• v.6 no.1
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• pp.13-18
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• 1984

To find out the effect of transplanting time on the autonomic characters, yield of cured leaves and content of polyphenols in burley tobacco, three transplanting time were evaluated. The results obtained are as follows. Low temperature which was caused damage earliest stage of tobacco in early transplanting could escape by vinyl mulching and other treatment. 2. The major polyphenols in leaves were chlorogenic acid and rutin, small amount of scopolin and quercetin were also detected. 3. Chlorogenic acid decreased during curing. 4. Polyphenols content was not influenced by transplanting time.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2021.11a
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• pp.114-115
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• 2021

In this study, the effects of thermal activation on the compressive strength and water absorption of fly ash-cement systems were studied. The results show that the increase in curing temperature improves the early-age compressive strength and reduces its water absorption.

• Journal of the Korea Concrete Institute
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• v.17 no.4 s.88
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• pp.551-558
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• 2005

The setting and hardening of concrete is accompanied with nonlinear temperature distribution caused by development of hydration heat of cement. Especially at early ages, this nonlinear distribution has a large influence on the crack evolution. As a result, in order to predict the exact temperature history in concrete structures it is required to examine thermal properties of concrete. In this study, the convection heat transfer coefficient which presents thermal transfer between surface of concrete and air, was experimentally investigated with variables such as velocity of wind, curing condition and ambient temperature. At initial stage, the convection heat transfer coefficient is overestimated by the evaporation quantity. So it is essential to modify the thermal equilibrium considered with the boiling effect. From experimental results, the convection heat transfer coefficient was calculated using equations of thermal equilibrium. Finally, the prediction model for equivalent convection heat transfer coefficient including effects of velocity of wind, curing condition, ambient temperature and boiling effects was theoretically proposed. The convection heat transfer coefficient in the proposed model increases with velocity of wind, and its dependance on wind velocity is varied with curing condition. This tendency is due to a combined heat transfer system of conduction through form and convection to air. From comparison with experimental results, the convection heat transfer coefficient by this model was well agreed with those by experimental results.

• 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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• 2005.05b
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• pp.441-444
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• 2005

Our country has experienced variations in temperature as belong to the area of the continental climate that shows four significant seasons. These occur immense difficulty on the period, cost, quality of construction. As the hydration of cement processes, the strength of concrete is developed. In order to improve the quality of concrete, various conditions including temperature and humidity should be maintained appropriately and concrete itself should be cured sufficiently. In the early age, the strength of concrete is developed remarkably. However, the hydration is accelerated too much in high temperature or delayed too much in low temperature, so the quality can be changed and It can fail to get the objective strength. This paper aims to offer the data, necessary to the quality control handbook.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.05b
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• pp.345-348
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• 2005

This paper presents the result of adiabetic temperature rise and fundamental properties of concrete combining admixtures. According to results, difference of setting time with I5.5hours is observed between S-P and R-F30 mixture. Based on the adiabetic temperature rise test, 8$^{circ}C$of heat producted occurs between E-P and R-F30 mixture. is applied to estimate the temperature rising under adiabetic curing condition, which exhibits closer consistency with tested value. The function mentioned above can account for the effect of dormant period in hydration process at early stage on hydration heat production. It reveals that the consideration of placing layer based on the mixture adjustment(E-P mixture at top layer and R-F30 mixture at bottom layer) in mass concreting will contribute to reduce hydration heat as well as alleviate tensile stress discrepancy between placing layer.