• Journal of the Korea institute for structural maintenance and inspection
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• v.12 no.6
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• pp.164-172
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• 2008

The heat of hydration for early aged mass concrete induces high temperature with the hydration. Control of the temperature difference across a section is an effective strategy to minimize the hydration heat induced cracks for the structures where internal restraint is dominant. The current prevention methods for hydration cracking show some limitations for the control of thermal gradients, and these limitations could make micro and macro cracks in surface and core of concrete. Especially cooling methods can decrease the increasing hydration temperature, but it can not prevent the problem while decreasing temperature. Consequently heating pipes are added simultaneously with the cooling pipes in order to control the temperature gradients between core and surface of the concrete, followed by the finite element analysis (FEA). Based on the FEA, the proposed method using cooling pipe and heating pipes together has been found to be an effective alternative in thermal gradient control, in terms of controlling temperature induced cracks significantly.

• Journal of the Korea institute for structural maintenance and inspection
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• v.17 no.3
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• pp.126-135
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• 2013

Recently, mass concrete with high flowability are widely used to improve the quality and constructability in the longer span construction of prestressed concrete bridges, but it may induce nonstructural cracks due to the hydration heat and autogenous shrinkage etc. The stresses in concrete were evaluated by various experiments and numerical analysis. The tensile stress in mass concrete was increased in connection with the accumulation of hydration heat. Moreover, large amount of autogenous shrinkage from powder type admixture could add the tensile stress to mass concrete near anchorage zone. The tensile stresses in anchorage zone by heat and autogenous shrinkage exceeded the tensile strength of early stage of concrete, and small amounts of stress increasement were shown in other parts of PSC girder.

• Journal of Korean Tunnelling and Underground Space Association
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• v.11 no.1
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• pp.37-45
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• 2009

In this study, experiments of development and application of 50 MPa high-performance concrete are performed for large dimensional tunnel linings. In order to produce 50MPa high-performance concrete, eight optimal mixtures replacing with fly ash and ground granulated blast furnace slag up to 50 percent of type I Portland cement were selected then tests for mechanical properties and simple adiabatic temperature rise tests were carried out. And in order to assess the quantitative characteristics of heat of hydrations of developed mixtures, three mixtures that the type I Portland cement (OPC) and each one mixture of binary and ternary mixtures (BS30, F15S35) were reselected, then the adiabatic temperature rise tests and mock-up tests were performed. Consequently, the comparisons between the results of mock-up tests and finite element analysis can be enhanced the reliability of analyzing routines of thermal behaviours of the developed high-performance concrete.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2017.11a
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• pp.77-78
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• 2017

In this study, the effect of insulation curing for mass concrete wall according to thickness and curing period was evaluated by thermal analysis.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2012.11a
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• pp.165-166
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• 2012

A thermal stresses by heat of hydration was analyzed according to a change of a pour height in reactor containment building. In case of more than 3.6m pouring height a crack index by heat of hydration analysis resulted in less than 1 because there is not a construction joint of vertical direction and for a self-restraint effect of circumferential section shape. Therefore detailed consideration on a mixture proportion of binder type, quantity in concrete and selection of a form in seasonal air temperature is needed for a control of tensile stress by heat of hydration.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.19 no.1 s.71
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• pp.15-25
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• 2006

The researches on the early-aged concrete hydration process and the techniques for the early-aged concrete crack control mainly have been focused and developed on the massive concretes in both experimental and numerical studies. However, those researches for relatively thin members such as the upper slab of the reinforced concrete rahmen bridge have nearly been attempted. In this study, a designing technique for crack controlling in the thin members of the early-aged reinforced concrete rahmen bridges based on measured temperature history, strength revelation model and sinkage model is proposed. A method of calculating the reinforcing bar area for crack controlling is also proposed and it is found that the distributing bars under the design loads become the main reinforcing bars in the temperature stress analysis of the early-aged reinforced concrete rahmen bridges. It is shown that the proposed analysis technique is able to use the design of crack control for the early-aged reinforced concrete rahmen bridge.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.6 no.3
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• pp.223-230
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• 2005

Lately, massive concrete structures are increasingly built. Mass concrete structures are cast in many stages with construction joints. Individually constructed segment exhibit different heat source properpies and time dependent properties. As such construction stages must be incorporated in a heat of hydration analysis model to truly reflect a real construction process. Thermal stress analysis is conducted to find the way of controlling the thermal crack of pier footing mat in this paper. The footing mat model fur the analysis is $12m\times14m$ area and 3m height. This study show the process of construction stage and analyzes the results for a foundation structure constructed in 2 stage pours.

• Journal of the Korean Geotechnical Society
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• v.19 no.6
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• pp.127-149
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• 2003

The bridge tested was 3 spans 90m-long PSC beam concrete bridge with a stub-type abutment which had a skew of 60$^{\circ}$ about the axis of bridge. A cement concrete was placed at the superstructural slab of the bridge. Inclinometers and straingauges were installed at piles as well. During 7 days-curing of superstructural slab, the pile behavior in response to hydration heat and drying shrinkage of the slab was monitored. Then monitored values were compared with the horizontal movement obtained from the HACOM program and the calculated lateral behavior obtained from the nonlinear p-y curves of pile. As a result, lateral behavior of H-piles by the field measurement occurred due to the influence of hydration heat and drying shrinkage obtained during curing of superstructural concrete. The lateral displacements by hydration heat and drying shrinkage were 2.2mmand 1.4mm respectively. It was observed as well that the inflection point of lateral displacement of pile was shown at 1.3m down from footing base. It means that the horizontal movement of stub abutment did not behave as the fixed head condition of a pile but behave as a similar condition. The measured bending stress did not show the same behavior as the fixed head condition of pile but showed a similar condition. The increment of maximum bending stress obtained from the nonlinear p-y curves of pile was about 300(kgf/$\textrm{km}^2$) and was 2 times larger than measured values regardless of installation places of straingauges. Meanwhile, lateral load, maximum lateral displacement, maximum bending stress and maximum bending moment of pile showed a linear behavior as curing of superstructural concrete slab.

• Journal of the Korea Concrete Institute
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• v.14 no.3
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• pp.382-391
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• 2002

This study is devoted to the problems of thermal and shrinkage stresses in order to avoid cracking at early ages. The early-age damage induced by volume change has great influence on the long-term structural performance of the concrete structures such as its durability and serviceability To solve this complex problem, the computer programs for analysis of thermal and shrinkage stresses were developed. In these procedures, numerous material models are needed and the realistic numerical models have been developed and validated by comparison with relevant experimental results in order to solve practical problems. A framework has been established for formulation of material models and analysis with 3-D finite element method. After the analysis of the temperature, moisture and degree of hydration field in hardening concrete structure, the stress development is determined by incremental structural formulation derived from the principle of virtual work. In this study, the stress development is related to thermal and shrinkage deformation, and resulting stress relaxation due to the effect of early-age creep. From the experimental and numerical results it is found that the early-age creep p)ays important role in evaluating the accurate stress state. The developed analysis program can be efficiently utilized as a useful tool to evaluate the thermal and shrinkage stresses and to find measures for avoiding detrimental cracking of concrete structures at early ages.

• Journal of the Korean Recycled Construction Resources Institute
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• v.3 no.4
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• pp.301-306
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• 2015

For the purpose of developing high performance marine concrete with improved crack resistance and durability, this analytical study aimed to estimate strength, hydration heat characteristics, and chloride attack resistance of concrete with mineral admixture. Ground granulated furnace slag and fly ash were considered for mineral admixture. The replacement of ground granulated furnace slag and fly ash considered in the analysis was in the range of 0~70% and 0~40 %, respectively. The analysis results indicated that both ground granulated furnace slag and fly ash decreased compressive strength, and the effect of adding ground granulated furnace slag on mitigation of hydration heat was limited whereas fly ash had an noticeable influence on it. It was also found that the replacement with ground granulated furnace slag enhanced the chloride attack resistance but fly ash deteriorated the resistance. From the analytical studies, It could be expected that a ternary blended cement composition with proper amount of ground granulated furnace slag and fly ash might be effective to control crack resistance as well as chloride attack resistance of marine concrete.