• Proceedings of the Korea Concrete Institute Conference
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• 1996.04a
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• pp.275-279
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• 1996

In this study, the effect of external restraint on the thermal stresses and thermal cracking mode in mass concrete are analysed using the two major factors affecting external restraint such as the ratio of width go height of the placed structure (L/H) and the elastic modulus of base structure (E). For this parametric study, many cases with different values of L/H and Er are analysed by the FEM program and the co-relationship of the those major factors is examined. To evaluate the effect of external restraint on the thermal behavior of placing structure, internal restraint stress caused by temperature difference is subtracted from total thermal stress. In the case of small value of L/H or Er, it shows as internally restricted mode indicating maximum tensile stress in surface at early age, and the external restraint makes the possibility of thermal cracking higher. However, in the case of the large values of L/H and Er, the crack index at center is smaller than at surface due to the effect of external restraint. Thus, the initial location of the thermal crack is shifted from the surface to the center and the resulting crack is formed at later age.

• Proceedings of the Korea Concrete Institute Conference
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• 1999.04a
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• pp.275-280
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• 1999

It was analysed the effect of pipe cooling as a measure to avoid thermal cracks due to the heat of hydration during the curing process of a massive prestressed concrete (PSC) slab. PSC slab has a complex three-dimensional shape of which the maximal and minimal thicknesses of cross-section were 2.8 and 0.95m, respectively. Steel pipes of which the diameter was 1 inch were employed for cooling. The horizontal and vertical distances between the contiguous pipes were 0.5 and 0.6m, respectively. One the four layers of cooling pipe were arranged according to the thickness of cross-section. Temperature distribution was calculated by the program developed by the authors, of which the accuracy was verified on a few published papers by the authors. Based on the temperature analysis of the cross-section which had four layers of cooing pipe, the maximum temperature of concrete interior was 54.2$^{\circ}C$ and the maximum differenced between the interior and surface temperatures of concrete was 14.$0^{\circ}C$ and, thereby, the thermal cracking index was 1.1. Upon the stress analysis, the thermal cracking index was 0.92 and the probability of thermal-crack development was 52%. Therefore, it was expected to make it possible to reduce the probability of thermal-crack development in a massive PSC slab by adopting pipe cooling.

• Structural Engineering and Mechanics
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• v.47 no.1
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• pp.1-25
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• 2013

A combined thermal and mechanical action in roller compacted concrete (RCC) dam analysis is carried out using a three-dimensional finite element method. In this work a numerical procedure for the simulation of construction process and service life of RCC dams is presented. It takes into account the more relevant features of the behavior of concrete such as hydration, ageing and creep. A viscoelastic model, including ageing effects and thermal dependent properties is adopted for the concrete. The different isothermal temperature influence on creep and elastic modulus is taken into account by the maturity concept, and the influence of the change of temperature on creep is considered by introducing a transient thermal creep term. Crack index is used to assess the risk of occurrence of crack either at short or long term. This study demonstrates that, the increase of the elastic modulus has been accelerated due to the high temperature of hydration at the initial stage, and consequently stresses are increased.

• Journal of the Korea Computer Industry Society
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• v.9 no.3
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• pp.99-104
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• 2008

The thermal stresses due to hydration heat in massive concrete structures are affected by ambient temperature and placing concrete temperature. It is needed to predict the thermal stresses considering ambient temperature and placing concrete temperature. In this study, hydration heat analyses of coping were carried out. After the maximum tensile stress was occurred at 2,75 days the crack index was increased. Therefore the possibility of crack occurrence was rare. The possibility of crack occurrence can be reduced by placing concrete temperature drop. Therefore some method to drop the placing concrete temperature may be effective to reduce the possibility of crack occurrence.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.05b
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• pp.445-448
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• 2006

In order to control the temperature crack of massive dam concrete, the selection of appropriate materials like binder, aggregates etc., is essential. To select the optimal mix proportion, ordinary portland cement(Type I) plus 25% of fly ash and low heat portland cement(Type IV) are used as binder, and 80mm of coarse aggregates are used to reduce the amount of binder and compare the compressive strength, hydration temperature and crack index. The results of this study are as following. 1. The strength of Type IV cement is advantageous on the long-term age. 2. According to the temperature measured on mock-up$(1.5m{\times}1.5m{\times}1.5m)$, and realized the thermal analysis, the Type IV cement carried out advantageous to control the thermal crack.

• 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).

• Journal of the Korea institute for structural maintenance and inspection
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• v.11 no.1
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• pp.57-67
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• 2007

The service life of concrete structure is to a great extent influenced by crack developed at early ages of concrete material. Especially, hydration heat is a main cause of thermal cracking at mass concrete structures. The thermal cracking of massive structure is analyzed of the thermal cracking index which was presented Concrete Standard Specifications. The thesis analyzed the thermal cracking index which considered various variable (cement type, height of casting, curing condition, concrete mixing temperature, the unit cement content) at internal restricted mass concrete. The analysis result is denoted increase and decrease rate of thermal cracking index whenever the variables change. The results is helped to understand thermal cracking every time structures is designed and constructed. And I think that it is useful economic and stable design of mass concrete structures.

• Journal of the Korea institute for structural maintenance and inspection
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• v.14 no.1
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• pp.156-164
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• 2010

A total of 6 stepwise constructions were made for building the floating mass concrete foundation. The optimal curing strategies and specialized construction guidelines were adoptively extracted from the 1.5m cube mock-up test prior to the main concrete work. Two different thermal crack index(TCI) calculations from current construction manual exhibit relatively low values as comparing the measured temperature data. This implies that the hydration-induced cracking could be developed in parts of concrete mass. However, the controversial phenomenons in reality were observed. No significant surface cracks are detected at the successive construction stages. Thereby, this paper raises the question regarding on the existence of characteristic length with varying size and shape of a target specimen which are missing in the current construction manual. The isothermal core area and high thermal gradient area in the edge volume should be identified and be introduced to TCI calculation for the purpose of an accuracy.

• Journal of Ocean Engineering and Technology
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• v.23 no.6
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• pp.111-116
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• 2009

The cracking due to hydration heat in mass concrete must be resolved to improve the stability and durability of concrete structures. In this study, the economic efficiency was improved by replacing a copper pipe with a steel one for the heat pipe, and the heat pipe was standardized to significantly improve the operation efficiency, such as the processing, transport, assembly, and construction time. As a result of the experiment, the peak temperature of the ICSHP, ISSHP, and ISUHP specimens decreased by about $7.2{\sim}10.9^{\circ}C$ compared to the OPC specimen and the probability of a thermal crack being generated in the ICSHP, ISSHP, and ISUHP specimens decreased by up to 84~88%.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.11a
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• pp.413-416
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• 2006

This paper presents the analytical results on the heat of hydration and induced thermal cracking of the wall elements in LiNAC that is a radioactive shield concrete structure. This wall elements measuring 1.2 m in thickness and 32 m in length tend to exhibit thermal cracking due to heat of hydration and high constraint effects caused by slab element located in the lower part of structure. In this analysis, four different construction stages were considered to find out the most effective concrete casting method in terms of thermal stress. Among the construction methods adopted in this analysis, the method of installation of construction connection measuring 1.2 m at the both side of wall elements was very effective way to control the thermal stress, resulting in increase thermal cracking index of wall elements in LiNAC structure. Finally, the wall elements in LiNAC structure was cast successfully according to the proposed construction method.