• Proceedings of the Korea Concrete Institute Conference
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• 2002.10a
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• pp.421-424
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• 2002

Concrete roof in In-Chon LNG tank #15~18 is a very important structure. Precise control of quality is needed. This roof has 0.6~1.5m thickness, 36.23m radius, and, 12.7m height. So in this structure thermal crack caused by hydration heat should be controled. In this project belite cement plus LSP concrete is used. As a result of ambient temperature rising test and thermal analysis using FEM, this belite cement plus LSP concrete is expected to control the thermal crack well.

• Computers and Concrete
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• v.18 no.5
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• pp.1041-1051
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• 2016

In this study, the construction of a reinforced concrete bridge pier was analyzed from durability point of view. The goal of the study is to analyze the crack iniation condition due to construction and present some recommendations for construction conditions of the reinforced concrete bridge pier. The bridge is located at the western port area of Shenzhen, where the climate is high temperature and humidity. To control the cracking of concrete, a construction simulation was carried out for a heat transfer problem as well as a thermal stress problem. A shrinkage model for heat produced due to cement hydration and a Burger constitutive model to simulate the creep effect are used. The modelling based on Femmasse(C) is verified by comparing with the testing results of a real underground abutment. For the bridge pier, the temperature and stress distribution, as well as their evolution with time are shown. To simulate the construction condition, four initial concrete temperatures ($5^{\circ}C$, $10^{\circ}C$, $15^{\circ}C$, $20^{\circ}C$) and three demoulding time tips (48h, 72h, 96h) are investigated. From the results, it is concluded that a high initial concrete temperature could result in a high extreme internal temperature, which causes the early peak temperature and the larger principle stresses. The demoulding time seems to be less important for the chosen study cases. Currently used 72 hours in the construction practice may be a reasonable choice.

• 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 Industrial Technology
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• v.26 no.A
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• pp.139-146
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• 2006

Many concrete bridge decks develop transverse cracking shortly after construction. These cracks accelerate corrosion of reinforcing steel and lead to concrete deterioration, damage to components beneath the deck, unsightly appearance. These cracks shorten the service life and increase maintenance costs of bridge structures. In this study, VES-LMC overlay, which provides the same benefits as a conventional overlay, is designed to cure very quickly. Although the materials for VES overlays are more expensive, the cost is more than offset by the savings on traffic control and work zone safety measures. Otherwise, reaction of hydration occurs very rapidly in beginning step(concrete placing). As a results, thermal cracking can be occur by thermal stress in accordance with hydration-heat The purpose of this study was to estimate diagnosis of crack occurrence of VES-LMC through field tests at early-age.

• Journal of the Korea Institute of Building Construction
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• v.15 no.1
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• pp.25-33
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• 2015

In this study, initial crack index was evaluated by FEM analysis to find the crack propagation from hydration heat in precast concrete. As results, as the usage of hardening accelerator increased, initial compressive strength increased and setting time was shortened. Additionally, as amounts of hardening accelerators increased, the central temperature of concrete increased and the time to reach the highest temperature was shortened. It was demonstrated that the hardening accelerators accelerated the hydration reaction of cement, and caused the increase of hydration heat within the short period of time. Furthermore, the crack index for evaluating the heat level was performed by FEM. As results, there was no problem about the cracks, despite of the growth of initial high hydration heat. This is because of the increased tensile strength that is large enough to sustain the thermally induced-stress.

• Proceedings of the Korea Concrete Institute Conference
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• 2003.11a
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• pp.293-296
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• 2003

The purpose of this study is to examine the effect of aluminium sulfate on setting time and compressive strength of cement mortar as focused on formation of ettringite by the reaction between aluminium sulfate and calcium hydrate. The specific parameter was the addition ratio of aluminium sulfate to cement mortar. After specimens made by admixing aluminium of 0~7% by weight of cement, respectively, to cement mixtures, the experimental items such as setting time, compressive strength and heat of hydration in this study were carried out. As a result of this study, it is possible that aluminium sulfate could be added into cement mixture from a standpoint of increasing early compressive strength as considering the setting time and heat of hydration.

• Magazine of the Korean Society of Agricultural Engineers
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• v.43 no.5
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• pp.124-131
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• 2001

The shrinkage properties of high early strength concrete were investigated. One of the method to control microcrack and crack development due to restrained shrinkage is to reinforce concrete with randomly distributed fibers. Regulated-set cement and two different types of fiber were adopted. The experiments for heat of hydration, drying and autogenous shrinkage were conducted. The desirable resistance of high early strength fiber reinforced concrete to restrained shrinkage microcracking was achieved. These results indicate that use of fiber in high early strength concrete plays an important role in control of crack development due to restrained shrinkage.

• Journal of the Korea Concrete Institute
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• v.22 no.3
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• pp.375-380
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• 2010

In this study, physical properties of cement blended with Finex-slag powder(OPC-FS) were investigated by the measurement of flowability, compressive strength, hydration heat, and $Ca(OH)_2$ content. In addition, those properties of the cement blended with blast furnace slag(OPC-BFS) were also measured for comparison. It was found that OPC-FS and OPC-BFS showed similar trend in the rheological properties. In the blended cement pastes with the $4,000\;cm^2/g$ Blaine value the flowability of OPCFS was better than that of OPC-BFS. The initial 3 day mortar compressive strength and the hydration heat of paste of OPC-FS was a bit higher, compared with OPC-BFS. Accordingly $Ca(OH)_2$ produced in the cement hydration was decreased very rapidly.

• Proceedings of the Korean Nuclear Society Conference
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• 1999.10a
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• pp.369.2-369
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• 1999

• Proceedings of the Korea Concrete Institute Conference
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• 2004.05a
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• pp.148-151
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• 2004

The hardening of concrete after setting 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 tensile cracking. As a result, in order to predict the exact temperature distribution in concrete structures it is required to examine thermal properties of concrete. In this study, the coefficient of air convection for concrete mix of nuclear power plant, which presents thermal transfer between surface of concrete and air, was experimentally investigated with variables such as velocity of wind and types of form. The coefficient of air convection obtained from experiment increases with velocity of wind, and its dependance on wind velocity is varied with types of form. This tendency is due to a combined heat transfer system of conduction through form and convection to air. The coefficient of air convection for concrete mix of nuclear power plant obtained from this study was well agreed with the existing models.