• Proceedings of the Korea Concrete Institute Conference
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• 2002.10a
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• pp.655-660
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• 2002

Major deterioration in concrete structures are salt attack and carbonation. Especially severe problems due to carbonation occur in tile concrete structures of city, tunnel, underground structures. Cracks in concrete during service life including early age due to hydration heat and/or shrinkage accelerate the diffusion of concrete so that the deterioration is also accelerated. In this study, carbonation depths of both non-cracked concrete and cracked concrete are evaluated and weight change test and TGA are carried out. Through the tests, a relation between water-cement ratio and carbonation depth is derived and also carbonation increase rate is derived in the function of crack width.

• Proceedings of the Korea Concrete Institute Conference
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• 1994.04a
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• pp.209-214
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• 1994

The heat of hydration of cement causes the intemal temperature rise at early age, particulay in massive concrete structures. As the results of the temperature rise and restraint condition, the thermal stress amy induce cracks in concrete. The prediction of the thermal stress is very important in design and consturction slages in order to control the cracks in mass concrete. In this study, the temperature rise of high strength concrete due to the heat of hydration is investigated. Test variables are type and content of binder. As the results, the temperature rise is imcreased with increasing cement content. However, the increament is decreased in higher cement comtnet range. Fly ash is effictive in the reduction of hydration heat.

• Proceedings of the Korea Concrete Institute Conference
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• 2002.05a
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• pp.29-34
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• 2002

The heat of hydration of cement causes the internal temperature rise at early age, paticular in massive concrete structures. As the results of the temperature rise and restraint condition, the thermal stress may induce cracks in concrete. The prediction of the thermal stress is important in design and construction stages in order to control the cracks in mass concrete. It is poor economy to analysis for prediction of the thermal stress on each design or construction. In this study, the hydration heat and thermal stress analysis is performed by ABAQUS program, as a results of thermal analysis, the formula of size-placing depth relationship is proposed.

• Proceedings of the Korea Concrete Institute Conference
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• 1992.04a
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• pp.107-113
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• 1992

The heat of hydration of cement the causes the internal temperature rise at early age, particulary in massive concrete structures such as a mat-slab of nuclear reactor building or a dam or a large footing. As the result of the temperature rise and restraint of foundation, the thermal stress enough to induce concrete cracks can occur. Therefore, the prediction of the thermal stress is very important in the design and construction stages in order to control the cracks developed in massive concrete structures. And, more creep and shrinkage take place at elevated temperatures in young concrete, Thus the effect of creep and shrinkage must be considered for checking the safety and servicebility(crack, durability and leakage).

• Proceedings of the Korea Concrete Institute Conference
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• 2004.11a
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• pp.273-276
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• 2004

Recently. cold weather constructions were popularized because of the importance of construction term. The special method about mix design and curing of concrete was being planned to conduct cold weather constructions, but these method were not considered in a low temperature time. A Strength revelation of concrete is delayed in a curing condition of low temperature. If a construction was loaded in this case, cracks or remaining deformations are generated in a construction. So, a strength revelation characteristic in early age was investigated to secure early strength of concrete in curing condition of a low temperature. In this study, the method about concrete mix design was presented to secure construction safety in a low temperature time.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 1992.10a
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• pp.67-72
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• 1992

The heat of hydration of cement causes the internal temperature rise at early age, particulary in massive concrete structures such as a footing of nuclear reactor building or a dam. As the result of the temperature rise and restraint of foundation, the thermal stress may induce cracks in concrete. Therefore, the prediction of the thermal stress is very important in the design and construction stages in order to control the cracks developed in massive concrete structures. And, in case of young concrete, creep effect by the temperature load is larger than That of old concrete. Thus the effect of creep must be considered for checking the cracks, serviceability, durability and leakage. This study is composed of two items. The first, it is to develop a finite element program which is capable of simulating the temperature history in mass concrete. The second, when the thermal stress of mass concrete structures considering creep is calculated by using the modified elastic modulus due to the inner temperature change. It is shown that the analytical results of this study is in comparably good agreement with JCI's analytical results.

• Journal of the Korea Institute of Building Construction
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• v.10 no.4
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• pp.113-122
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• 2010

In this study, 150MPa ultra-high-strength concrete was manufactured, and its performance was reviewed. As technically meaningful autogenous shrinkage reportedly occurs at a W/B ratio of 40% or less, although it occurs in all concrete regardless of the W/B ratio, the effects of the use of expansive admixture and shrinkage reducer, or of the friction and restraint of forms that may result in the effective reduction of autogenous shrinkage, were reviewed. As a result, considering the flow and strength characteristics, it was found that the slump flow time was shorter with expansive admixture, and shortest with shrinkage reducer. All specimens with $30kg/m^3$ expansive admixture showed high strength at early material age. Their strength decreased due to the expansion cracks when there was excessive use of expansive admixture, and the use of shrinkage reducer did not influence the change in the strength according to the material age. The expansive admixture had a shrinkage reduction effect of 80%, while the shrinkage reducer had a shrinkage reduction effect of 30%, indicating that the expansive admixture had a stronger effect. It seems that mixing the two will have a synergistic effect. The shrinkage reduction rate was highest when the W/B ratio was 20%. The form suppressed the expansion and shrinkage at the early period, and the demolding time did not significantly influence the shrinkage. The results of the study showed that the excessive addition of expansive admixture leads to expansion cracks, and the expansive admixture and shrinkage reducer have the highest shrinkage reduction effect when they are mixed.

• International Journal of Highway Engineering
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• v.6 no.4 s.22
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• pp.75-89
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• 2004

Long term performance of concrete pavement significantly depends on the given construction and environmental condition. It means that random cracks and extreme crack width due to inappropriate quality control at the early age might lead to decreasing the pavement service life. The temperature and moisture during the construction, cement and aggregate types, curing condition are major components to affect the quality of the concrete pavement at the early age. First of all, the high temperature differential, that is made by increasing air temperature and the heat of cement hydration, is known as the major contributor to severe cracks. In this study, tent covering was used for controlling temperature of the concrete slab. The field measurement data indicates that the effect of the tent covering is very significant to decrease possibilities of random crack occurrence and curling stress and enhance the long-term concrete strength. HIPERPAV(High PERformance PAVing software), a program predicting the strength and stress of an earty-age concrete pavement (72 hour after placement), is used for simulating the effects of tent covering. The HIPERPAVE results showed that the section with the tent covering has higher reliability than the section without the tent covering by 22.5%. In details, reliability is increased 72.5% (without the tent covering) to 95% (with the tent covering).

• KSCE Journal of Civil and Environmental Engineering Research
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• v.14 no.4
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• pp.771-781
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• 1994

The heat generation of cement causes the internal temperature rise and volume change at early age, particulary in massive concrete structures. As the results of the temperature rise and restraint conditions, the thermal stress may induce cracks in concrete. Therefore, the prediction of the thermal stress is very important in the design and construction in order to control the cracks developed in mass concrete. In case of young concrete, creep effect by the temperature load is larger than that of old concrete. Thus, the effect of creep must be considered for checking the cracks, serviceability, durability and leakage. This paper is concentrated on the development of a finite element program which is capable of simulating the temperature history and the thermal stress considering creep and the modified elastic modulus due to inner temperature change and maturity. The analytical results in the inner parts highest important to control cracks are in good agreement with experimental data. Therefore this study may provide available method to control the cracks.

• Journal of the Korea institute for structural maintenance and inspection
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• v.7 no.2
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• pp.159-167
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• 2003

Cracks in reinforced concrete structures reduce overall durability by allowing the penetration of water and aggressive agents, thereby accelerating the deterioration of the reinforcing steel. Highway pavement and bridge decks are especially susceptible to this type of deterioration since these structures exhibit high rates of shrinkage and are frequently exposed to aggressive environmental conditions. The objectives of this investigation included the development of experimental procedures for assessing shrinkage cracking potential of recycled aggregate concrete, the evaluation of mix composition on shrinkage cracking potential, and the development of theoretical models to simulate early-age cracking behavior. Specifically, the influences of shrinkage-reducing admixture(SRA) and recycled aggregate concrete were investigated. The shrinkage-reducing admixture substantially reduces free shrinkage and restrains shrinkage cracking while providing similar mechanical properties. A fracture mechanics modeling approach was developed to predict the behavior of a variety of restrained concrete specimens. This modeling approach was used to successfully explain experimental results from a variety of mixture compositions. The model was used to demonstrate the influence of material and structural properties on the potential for cracking.