• Journal of the Korea Concrete Institute
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• v.18 no.6 s.96
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• pp.769-776
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• 2006

Recently, owing to the development of industry and the improvement of building techniques, concrete structures are becoming larger and higher. In hardening of these large connote structures, the heat of hydration gives rise to considerable thermal stress depending on the size and environmental condition of concrete, which might cause thermal cracking. Especially, the crack may cause severe damage to the safety and the durability of concrete structure. This study investigates the thermal properties of concrete according to several binder conditions, such as OPC, Belite rich cement(BRC), slag cement(SC), blast furnace slag(B) added cement fly ash(F) added cement and blast-furnace-slag and fly ash added cement. As a result of this study, the properly of concrete is most better BRC than others, and fly ash(25%) added cement and BFS(35%)-fly ash(15%) added cement gets superior effect in the control of heat hydration. But synthetically considered properties of concrete, workablity, strength heat hydration, etc, it is more effective to use mineral admixture. Especially, to be used Blast Furnace slag is more effective.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2008.05a
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• pp.57-60
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• 2008

This study investigated the results of insulation heat curing method using double layer bubble sheet in slab concrete and mass concrete in cold weather environment. First of all, when double bubble sheets are applied, it was shown that slab concrete was protected from early freezing by remaining between 6 and 15℃ even in case outside temperature drops -9℃ below zero until the 2nd day from piling, and in the case of mass concrete, with the maximum temperature difference between the center and surface less than 4℃, crack occurrence index was close to 2 and no hydration heat crack occurred by internal constraint. The insulation heat preservation curing method using the double bubble sheet applied in this field prevented early freezing owing to stable curing temperature management, deterring concrete strength development delay at low temperature, and obtained the needed strength. Also, it was proven that the method is highly effective and economic for cold weather concrete quality maintenance through curing cost reduction like construction period shortening and labor cost reduction, etc by reducing the process of temporary equipment installation and disassembling.

• Journal of the Korean Ceramic Society
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• v.19 no.2
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• pp.133-138
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• 1982

Two kinds of clinker liquid melts, one containing 2.0% of $K_2O$ and the other without $K_2O$, were prepared with the similar composition as those developed during the firing of portland cement clinker. One portion of melt was quenched and found to consist of glass together with traces of proto-$C_3A$, and the other portion was allowed to cool spontaneously to crystallize $C_3A$ and calciumferrite well. The product obtained by crystallization of the melt without $K_2O$showed cubic $C_3A$, while orthorhombic $C_3A$ was formed from the crystallized product containing $K_2O$. Studies on the hydration behavior of the samples made from the melts with 30% of gypsum were carried out for 24 hours by observation at regular intervals ettringite, monosulphate hydrates and gypsum which were formed or consumed during hydration. The samples without $K_2O$ in the melts were hydrated wth addition of proper amount of $K_2SO_4$ in the water for hydration. Hydration behavior of glassified $C_3A$ showed that it has low reactivity relative to crystallized $C_3A$, and also hydration reactivity of orthorhombic $C_3A$ was much lower than that of cubic $C_3A$ in 60 minutes. Potassium sulphate in the solution reduced the hydration reactivity of $C_3A$ . Evolution peaks of hydration heat examined by twin-type conduction micro-calorimeter showed that glassified $C_3A$ without $K_2O$ had secondary peak after 9 hours and $C_3A$ containing $K_2O$ after 12 hours. When crystallized $C_3A$ was hydrated, initial peaks of hydration heat were considerably high and there was no secondary peak for cubic $C_3A$ but the secondary peak of orthorhombic $C_3A$ appeared after 4 hours.

• Proceedings of the Korea Concrete Institute Conference
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• 1999.10a
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• pp.775-778
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• 1999

Accelerated chloride diffusion tests were carried out to estimate the chloride diffusion coefficient of concrete using ordinary portland cement, low heat belite-rich portland cement, and sulphate resistant portland cement. Concrete using low heat belite-rich portland cement showed a high diffusion coefficient due to delayed hydration of low heat belite rich portland cement, while the diffusion coefficients of concrete using sulphate resistant portland cement and ordinary portland cement were low.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2009.04a
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• pp.315-318
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• 2009

본 논문에서는 해상 기초 교각 매스 콘크리트의 수화열 저감 방안을 다루었다. 저발열 콘크리트, Mesh형 거푸집 공법 등에 대한 실험을 수행하여 각각의 수화열 저감효과를 평가하였다. 현장 실험은 사용 시멘트와 거푸집의 종류, 거푸집의 사용 면수에 따라 총 4 type으로 구성하였으며, 이에 대한 실험 결과와 유한 요소 해석 결과를 비교, 검증하여 최종적인 수화열 저감 성능을 도출하고자 하였다. 실험을 통해, 저발열 시멘트와 유로폼을 사용하는 것이 수화열 저감을 위해 효과적인 방법으로 판명되었으나 추가 공사비의 발생으로 효율성이 떨어질 것으로 판단된다. 또한 Mesh형 거푸집 적용 면 수와 온도 상승 저감 효과는 비례하는 것을 알 수 있었지만 내 외부 온도차가 다소 크게 나타나 수화열에 의한 균열 발생 확률면에서는 다소 불리하게 나타났다. 그러나 실험 단계에서 생략된 양생과 관리를 통하여 균열의 저감효과를 거둘 수 있을 것으로 판단되며, 추가적으로 거푸집 해체 단계를 생략함으로 공기단축 측면에서 유리할 것으로 판단된다.

• Proceedings of the Korea Concrete Institute Conference
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• 1998.04a
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• pp.199-204
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• 1998

To analysis the failure character of Low-Heat concrete which is used to prevent the thermal crack caused by hydration heat, static loading test was performed by this test method, "Determination of the Fracture Energy of Motar and Concrete by Means of Three-Point Band Tests on Notched Beam" (suggested by RILEM 50-FMC Committe). This study compared and analysised the fracture energy of Mode I (opening mode), the most general pattern in the view of water-cemente ratio(W/C), compressive strength and age of Ordinary Portland Concrete and Low-Heat Concrete under the same mixture. The test results show that the case of Ordinary Portland Concrete and Low-Heat Concrete, low Water-Cemente ratio(W/C) cause the increase of fracture energy, and high failure-strength decrease failure-deflection, and the fracture energy of Low-Heat Concrete is similar to Ordinary Portland Concrete as the age increase. increase.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2014.11a
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• pp.13-14
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• 2014

Ultra high performance concrete (UHPC) consists of cement, silica fume (SF), sand, fibers, water and superplasticizer. Typical water/binder-ratios are 0.15-0.20 with 20-30% of silica fume. The development off properties of hardening UHPC relates with both hydration of cement and pozzolanic reaction of silicafume. In this paper, by considering the production of calcium hydroxide in cement hydration and its consumption in the pozzolanic reaction, a numerical model is proposed to simulate the hydration of UHPC. The degree of hydration of cement and degree of reaction of silica fume are obtained as accompanied results from the proposed hydration model. The properties of hardening UHPC, such as degree of hydration of cement, calcium hydroxide contents, and compressive strength, are predicted from the contribution of cement hydration and pozzolanic reaction. The proposed model is verified through experimental data on concrete with different water-to-binder ratios and silica fume substitution ratios.

• 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.

• Applied Chemistry for Engineering
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• v.3 no.3
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• pp.507-515
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• 1992

This study was carried out to investigate the heat-storage/-release characteristics of the thermochemical reaction of the calcined dolomite and steam system for the application of regenerative heat exchangers with the packed bed shape experimental apparatus. The experimental data were obtained at the following conditions ; the hydration temperature was $150-400^{\circ}C$, the dehydration temperature was $700-800^{\circ}C$ and the steam mass flow rates were 294, 430 and 567 g/hr. In the present study, it was found that MgO of the calcined dolomite was not hydrated during the hydration process under the studied experimental conditions. Therefore, MgO of the calcined dolomite can be regard as an inert material. Because the reaction was proceeded from the packed bed input to packed bed output and from wall to center, it could be thought that the rate determining step is not the reaction itself but the heat transfer.

• Computers and Concrete
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• v.26 no.5
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• pp.429-438
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• 2020

To shorten the construction times of nuclear facility structures, three high-strength concrete mixtures were developed with specific consideration given to their curing temperatures, their economic efficiency, and the practicality of their quality control. This study was conducted to examine the temperature rise profiles of these three concrete mixtures and the potential for early-age thermal cracking in the primary containment vessel of a nuclear reactor with a wall thickness of 1200 mm. The one-layer placement height of the concrete for the primary containment vessel was increased from the conventional 3 m to 3.5 m. A nonlinear finite element analysis (FEA) was conducted using the thermal properties of concrete determined from the isothermal hydration and adiabatic hydration tests, and tuned through comparisons made with temperature rise profiles obtained for 1200-mm-thick mock-up wall specimens cured at temperatures of 5, 20, and 35℃. The hydration heat performance of the three concrete mixtures and their potential to produce thermal cracking in nuclear facilities indicate that the mixtures have considerable potential for practical application to the primary containment vessel of a nuclear reactor at various curing temperatures, fulfilling the minimum requirements of the ACI 301 and minimizing the likelihood of the occurrence of thermal cracks.