• Proceedings of the Korean Institute of Building Construction Conference
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• 2013.05a
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• pp.115-116
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• 2013

Property of the compressive strength of high strength concrete was investigated in adiabatic temperature history considering hot-weather conditions. As a result, compressive strength of specimens subjected to high temperature history showed more than 120% at 3days of age compare to standard cured specimens. But, at 91days of age showed the incidence of strength less than 100%.

• Journal of the Korea Institute of Building Construction
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• v.14 no.3
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• pp.273-284
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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 to 0.20 with 20 to 30% silica fume. In the production of ultra-high performance concrete, a significant temperature rise at an early age can be observed because of the higher cement content per unit mass of concrete. 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 ultra-high performance concrete. The heat evolution rate of UHPC is determined from the contributions of cement hydration and the pozzolanic reaction. Furthermore, by combining a blended-cement hydration model with the finite-element method, the temperature history in the hardening of UHPC is evaluated using the degree of hydration of the cement and the silica fume. The predicted temperature-history curves were compared with experimental data, and a good correlation was found.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2006.11a
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• pp.87-90
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• 2006

This study investigates the temperature history of slab mock-up specimens for hot weather concreting applying various surface insulating methods, in order to improve concrete quality at hot weather condition. Test showed that the use of insulating blanket or a bubble sheet on upper section of slab prevented from abrupt increase of temperature and vaporization of moisture during early curing at hot weather circumstance. In addition, it secured higher strength at early age. Therefore it is concluded that concrete construction insulating with the bubble sheet will reduce the plastic and drying shrinkage as well as improve strength at early age, thus securing concrete duality.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.11a
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• pp.685-688
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• 2006

As the concrete structure being large-sized and/or high-strengthened, the control of the hydration and curing temperature is made much account. This study, analysing the concrete temperature history from cylindric specimen and mock-up structures, investigates the effect of the early age curing condition and the optimum method of curing temperature control on mass concrete.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2012.11a
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• pp.51-53
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• 2012

This paper is to report the results of mock-up test for concrete during severe cold weather. The temperature is fixed at -20℃. The mock-up specimens were fabricated simulating slab, wall and column. Heating coil with different heat capacity with 5 W and 15 W were embedded at slab specimen. Test results revealed that at -20℃, temperature dropped below 0℃ since around 70 hours. It takes 7 days to gain 45°D·D of maturity for avoiding frost damage at early age.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2003.05a
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• pp.7-11
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• 2003

This study investigate the hydration heat history with variation of surface insulating material in cold weather concreting. According to the results, the temperature of concrete lowers below zero in 24hours, so early frost damage occurs in the case of exposure and 1 fold bubble sheet, but the lowest temperature keeps above zero, so a adiabatic effect is very favorable in the case of double bubble sheet and 부직포. Compressive strength of core specimen at 7 and 28 days is highest In the case of double bubble sheet and 부직포. But, considering convenience of construction and economical efficiency, it is thought that the most effective surface insulating material is 1 fold bubble sheet +blanket.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2013.05a
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• pp.75-77
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• 2013

In this study, the characteristics of temperature history was evaluated for three hot wires with different capacity installed in slab concrete which are relatively thin. Results can be summarized as follows. First, for the case of material using 5W hot wire, all decreased to below zero at or around 24 hours. Similarly, the material using 20W hot wire decreased to 2℃ below zero at or around 80 hours but satisfied the accumulative temperature of 45° D·D at 7 days of material age. On the other hand, the case of 30W hot wire, the biggest capacity, showed the high temperature history of 5℃ in average at all areas except the corners. Thus, the target accumulative temperature was secured at or around the 3 days of material age. Considering the above, the initial damage by freezing can be prevented only if 20W or higher hot wires are used for the slabs at -10℃ of extremely low temperature environment.

• Nuclear Engineering and Technology
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• v.44 no.5
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• pp.523-534
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• 2012

The objective of this study was to experimentally investigate the effect of heat curing methods on the temperature history and strength development of slab concrete exposed to $-10^{\circ}C$. The goal was to determine proper heat curing methods for the protection of nuclear power plant structures against early-age frost damage under adverse (cold) conditions. Two types of methods were studied: heat insulation alone and in combination with a heating cable. For heat curing with heat insulation alone, either sawdust or a double layer bubble sheet (2-BS) was applied. For curing with a combination of heat insulation and a heating cable, an embedded heating cable was used with either a sawdust cover, a 2-BS cover, or a quadruple layer bubble sheet (4-BS) cover. Seven different slab specimens with dimensions of $1200{\times}600{\times}200$ mm and a design strength of 27 MPa were fabricated and cured at $-10^{\circ}C$ for 7 d. The application of sawdust and 2-BS allowed the concrete temperature to fall below $0^{\circ}C$ within 40 h after exposure to $-10^{\circ}C$, and then, the temperature dropped to $-10^{\circ}C$ and remained there for 7 d owing to insufficient thermal resistance. However, the combination of a heating cable plus sawdust or 2-BS maintained the concrete temperature around $5^{\circ}C$ for 7 d. Moreover, the combination of the heating cable and 4-BS maintained the concrete temperature around $10^{\circ}C$ for 7 d. This was due to the continuous heat supply from the heating cable and the prevention of heat loss by the 4-BS. For maturity development, which is an index of early-age frost damage, the application of heat insulation materials alone did not allow the concrete to meet the minimum maturity required to protect against early-age frost damage after 7 d, owing to poor thermal resistance. However, the combination of the heating cable and the heat insulating materials allowed the concrete to attain the minimum maturity level after just 3 d. In the case of strength development, the heat insulation materials alone were insufficient to achieve the minimum 7-d strength required to prevent early-age frost damage. However, the combination of a heating cable and heat insulating materials met both the minimum 7-d strength and the 28-d design strength owing to the heat supply and thermal resistance. Therefore, it is believed that by combining a heating cable and 4-BS, concrete exposed to $-10^{\circ}C$ can be effectively protected from early-age frost damage and can attain the required 28-d compressive strength.

• Journal of the Korea Concrete Institute
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• v.15 no.5
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• pp.662-669
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• 2003

Recently, the serviceability and durability of concrete structures under thermal load have received great attention. The thermal stress and clacking behavior of concrete at early ages are one of the important factors that affect such serviceability and durability of concrete structures. Nevertheless, most studies on the behavior of early-age concrete have been confined to the temperature and strain development itself in the laboratory. The desirable efforts to explore the material properties of concrete at early-ages have not been made extensively so far. The purpose of the present study is, therefore, to identify some important material properties that affect the stress behavior of concrete at early-ages. To this end, full-scale concrete base-restrained wall members have been fabricated, and many sensors including thermocouples, strain meters and stress meters were installed inside of the wall members. These sensors were to measure the development of temperatures, strains and stresses at several location in concrete walls during the hardening and curing phase of early-age concrete. By using these measured values of strain and stress, the compliance function at early-age was identified. The basic form of compliance function derived in this study follows the double-power law. However, the results of present study indicate that the values of existing compliance functions are much lower than actual values, especially at very early-ages. It can be seen that the prediction of stresses of early-age concrete based on the proposed compliance function agrees very well with test data. The present study allows more realistic evaluation of varying stresses in early-age concrete under thermal load.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2013.11a
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• pp.23-25
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• 2013

In this study, the results are compared with the case of the concrete with embedded heating wire to verify the performance of the IB made in order to improve the workability and affordability, and to determine the effectiveness of early frost damage prevention. The IB was made using the 5W heating wire and layed on the upper surface of the concrete. The temperature was reduced to below 0℃ approximately within 24 hours, then approached the external temperature thereafter. On the other hand, when the 20W heating wire was used to make the IB and applied the same way, the temperature remained around -2 to 3℃ on the average even through the temperature was reduced to below 0℃, due to the heating wire with relatively large heating capacity. It appeared to reach 85% of the direct heating by embedding the heating wire relatively deeper in the concrete. However, it was determined that using the IB made with the 20W heating wire will prevent the early frost damage to some degree in -10℃.