• Journal of the Korea Concrete Institute
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• v.13 no.6
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• pp.536-543
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• 2001

Nowadays, with high-stoned and large-sized of structures, high-strength concrete is applicable to various methods. When high-strength concrete is used jointly with system form, seizing on the development of compressive strength at early age is very important in aspect of construction process. Because system form is stripped more faster than ordinary form. But, we have little data of compressive strength before system-form is stripped, and it isn't yet established that decision criterion of the time when system-form is stripped. So this paper deals with the development of compressive strength at early age before system-form is stripped. In this study, the experimental results indicate the boundary of curing temperature and mixing factor that is able to get needful early-strength in the application of slip-form method, and curing temperature must be kept over 15 degrees in winter season.

• Journal of the Korea Concrete Institute
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• v.14 no.2
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• pp.137-147
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• 2002

Maturity models involving curing temperature and curing ages have been widely used to predict concrete strength, which can accurately estimate concrete strength. However, they may not consider physical quantities such as the characteristics of hydrates and the capillary porosity of microstructures associated with strength development. In order to find out the effects of both factors on a strength increment, the hydration model and the estimation method of the amount of capillary porosity were established, and the compressive strength test of concrete nth various water/cement ratios was carried out considering two test parameters, curing temperature and curing age. In this study, by analyzing the experimental results, a strength estimation model for early-age concrete that can consider the microstructural characteristics such as hydrates and capillary porosity was proposed. Measured compressive strengths were compared with estimated strengths and good agreements were obtained. Consequently, the proposed strength model can estimate compressive strength of concrete with curing age and curing temperature within an acceptable error.

• Magazine of the Korea Concrete Institute
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• v.7 no.1
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• pp.126-135
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• 1995

The strength development of PFA concretes were invest~gated in this study. The work undertaken was divided into two parts which considered both the influence of PFA replacement level up to 45% and the effect of cement type at the high PRA leveI(45%). The additiorlal cement considered included a rapdhardemng portland ccnlent. The full range of concrete struc tural grades were studied anti ciight cu~ing contlltiorls covering those 11:ied 111 practlce were examined. The early strength retluced wit11 increasing PFA content. However, post 28days, the reverse was observed. It was posslhle through the use of rapid hardening portland cement at the high PFA level to achieve similar early strength to OPC concrete, with the same benefits noted above also being obtained post 28 days. The compressive strength uf hlgh PYA content concrt:tes at hgh temperature m s found to be higher than the ccmtrol at all ages hoth in water and alr. The same trends were observed at low t.ernperature in air. However, the reverse occur-ed at the low temperature In water.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.909-912
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• 2008

Fiber is an important ingredient in strain-hardening cementitious composite (SHCC), which can control fracture of cementitious composite by bridging action. The properties of reinforcing fiber, as tensile strength, aspect ratio and elastic modulus, have great effect on the fracture behavior of SHCC. But SHCC has serious problem as drying shrinkage because silica powder is used to make SHCC in order to improve bond strength between reinforcing fibers and cement matrix. Therefore, curing method (period and temperature) is very important for SHCC to show high tensile performance. a variety of experiments have being performed to access the performance of SHCC recently. This research emphasis is on the mechanical properties of SHCC made in Polyvinyl alcohol (PVA), Polyethylene (PE) fibers and steel cord (SC), and how curing method affects the composite property, and ultimately its strain-hardening performance.

• Journal of the Korea Institute of Building Construction
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• v.16 no.1
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• pp.67-76
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• 2016

Concrete exposed to severely low temperature below $-20^{\circ}C$ should be provided with proper heat supplying curing to protect the concrete from early frost damage at the time of pouring.meanwhile, so far, effective heat curingmethods of the concrete under severely low temperature are not well established in Korea. For this reason, the objective of this paper is to provide effective heat curingmethod of concrete exposed to severely low temperature to protect early frost damage by varying the combination of heat curingmaterial combinations. Temperature history,maturity development and core strength results are investigated. Fourmock-up specimens simulating slab, wall and column were prepared and heat insulation, heat supplying and both were applied. Test results indicate that the combination of quadruple layer bubble sheet(4BS) and embedding of heating cable has desirable performance for a slab, and heat supplying curing inside heat enclosure and heat generationmat also shows desirable performance for a wall, and for a column, use of EPS heat insulation has proper performance against early frost damage, which reaches $45^{\circ}D{\cdot}D$ and helps the concretemaintain above $0^{\circ}C$ within 3 days. Themethodsmentioned above are believed to be optimum protection from early frost damage of the concrete under $-20^{\circ}C$.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2021.11a
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• pp.131-132
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• 2021

According to the domestic specification, the curing of the specimen for strength management used to determine the time of the mold deformity of the structure concrete in early spring and early autumn is cured in the field structure condition. However, when the seal curing is performed in the field, the temperature of the specimen is very low compared to the temperature of the actual structure, so the strength of the structure concrete predicted based on the strength of the specimen is much undervalued than the actual one, which causes the mold to be deformed. Therefore, this study analyzed the temperature history and compressive strength characteristics of the specimen for strength management through other sealing curing at 5℃ and concrete of the actual structure, and presented the most suitable curing method.

• Magazine of the Korea Concrete Institute
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• v.7 no.4
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• pp.109-118
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• 1995

The permeability of concrete is closely related to the durability and the latter may be expressed by measuring permeability of concrete. According to the results, the permeability of fly ash concrete was lower than that of OPC(PC1) concrete and decreased with increasing fly ash levels(l5%, 30% and 45%). The permeability values of concrete cured in water is significantly lower than those of concrete cured in air, but the differences were reduced with increasing fly ash level. In comparison with OPC(PC1) concrete and high fly ash concrete containing enhanced early strength cements, the latter also had a lower permeability than the former. The permeability of concrete cured in water was decreased with curing time(28 and 180 days) irrespectwe of cement types. However, the trend of results cured in air was opposite to that cured in water due to the rnicrocrackinp: of concrete. It was found that the properties of strength and permeability of concrete were related each other. However, the permeability of concrete was more dependant upon the type of binder used in concrete.

• Korean Journal of Agricultural Science
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• v.14 no.2
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• pp.345-357
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• 1987

This study was performed to obtain the basic data which can be applied to improve the early strength of concrete. The results obtained were as follows; 1. In case that water reducing-set accelerating agent was added 0.75% of the weight of cement, the weight of water was reducd 10%. And $CaCl_2$ did nearly not have an effect on the w/c ratio. 2. Compressive strength and tensile strength increased 25%, 43%, respectively, in case that $CaCl_2$ was 2.0% of the weight of cement, and showed 120%, 140%, respectively, in case that water reducing-set accelerating agent was 0.75% of the weight of cement. 3. In case of steam curing at $60^{\circ}C$, the strength increased with the ages. At $100^{\circ}C$, the increase of strength in 1 age was two times as compared with plain concrete. After 7ages, the strength was similer to plain concrete. 4. The relationship between compressive strength and tensile strength was linear and was highly significant in cases of plain concrete, $CaCl_2$ concrete, C-W concrete, steam cured concrete, respectively.

• Journal of the Korea institute for structural maintenance and inspection
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• v.18 no.6
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• pp.114-122
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• 2014

Currently, global warming has become a serious problem arising from the usage of fossil fuels such as coal and petroleum. Moreover, due to the global warming, heat wave, heavy snow, heavy rain, super typhoon are frequently occurring all over the world. Due to these serious natural disasters, concrete structures and infrastructures are seriously damaged or collapsed. In order to handle these problems, climate change oriented construction technology and codes are necessary at this time. Therefore, in this study, the validity of the present concrete mixture proportions are evaluated considering temperature and humidity change. The specimens cured at various temperature and humidity conditions were tested to obtain their compressive and split tensile strengths at various curing ages. Moreover, performance based evaluation (PBE) method was used to analyze the satisfaction percentage of the concrete cured at various condition. From the probabilistic method of performance evaluation of concrete performance, feasibility and usability can be determined for future concrete mix design.

• Journal of the Korea Institute of Building Construction
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• v.16 no.4
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• pp.305-311
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• 2016

This study examined the long-term inelastic characteristics, including unrestrained shrinkage and creep, of low-heat cement concrete under different ambient curing temperatures. To achieve the designed compressive strength of 42MPa, water-to-binder ratios were selected to be 27.5, 30, and 32.5% for curing temperatures of 5, 20, and $40^{\circ}C$, respectively. Test results showed that the shrinkage strains of concrete mixtures tended to decrease with the decrease in curing temperature because of the delayed evaporation of internal capillary and gel waters. Meanwhile, creep strains were higher in concrete specimens under lower curing temperature due to the occurrence of the transition temperature creep. The design models of KCI provision gave better accuracy in comparison with test results than those of ACI 209, although a correction factor for low-heat cement needs to be established in the KCI provision.