• Proceedings of the Korea Concrete Institute Conference
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• 2000.10b
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• pp.1211-1214
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• 2000

The purpose of this paper was to study of blast furnace slag cement of high early strength and replacement ordinary portland cement. we prepared the specimens of cement and concrete with various mixing proportions of elementary materials. For example, clinker, gypsum(1~10%), fineness $4, 000~6, 000cm^2/g$ of blast furnace slag(30~50%), limestone etc. As a result of this study, fineness $(4, 000cm^2/g)$ blast furnace slag was of used replacement ordinary portland cement and fineness $(6, 000cm^2/g)$ blast furnace slag was of used blast furnace slag cement of high early strength.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2023.11a
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• pp.75-76
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• 2023

In the cement industry, various research initiatives are underway to achieve carbon neutrality. Mineral carbonation is a technology that converts carbon dioxide into minerals for storage, and CO₂ reactive hardening cement is a type of cement that incorporates mineral carbonation technology. In this study, we aimed to manufacture CO₂ reactive hardening cement for reducing carbon emissions in the cement industry by utilizing waste concrete powder generated in the construction sector.

• Journal of the Korea Institute of Building Construction
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• v.22 no.1
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• pp.35-43
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• 2022

The aim of this work was to a comparative review the performance of high calcium silicate cement (HSCSC) and that of ordinary Portland cement(OPC) and blast furnace slag cement(S/C). The result of the compressive test confirmed that the compressive strength development rate of high calcium silicate cement concrete at the age of 3 days was 73.6% that of ordinary Portland cement concrete. However, at the age of 28 days, the strength development rate of high calcium silicate cement increased to about 107.0% compared to ordinary Portland cement. In addition, the test of the chloride ion penetration resistance of concrete showed that at the age of 28 days, the passed charge decreased by 73.4% and 93.0%, respectively, in blast furnace slag cement and high calcium silicate cement compared to ordinary Portland cement, and at the age of 56 days, it decreased by 79.1% and 98.3%, exhibiting excellent resistance to chloride ion penetration. In particular, it was confirmed that the rate of decrease in the passed charge with age was higher in high calcium silicate cement than in ordinary Portland cement and blast furnace slag cement.

• Journal of the Korea Institute of Building Construction
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• v.4 no.3
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• pp.143-151
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• 2004

The purpose of this study is development of technique to use cementitious powder as recycle cement produced from deteriorated Concrete waste which has a large quantity of calcium carbonate. Therefore, after having theoretical consideration based on the properties of high-heated concrete and concerning about neutralization of Concrete, we analysis chemical properties of ingredients of cementitious powder. After making origin cement paste, then processing the accelarated carbonation, we consider the properties of hydration and chemical properties of cementitious powder under various temperature conditions. As a result of the thermal analysis, the $CaCO_3$ content of cementitious powder would affect decision of heat temperature to recover its hydrated ability because $CaCO_3$ content is increased when neutralization is progressed. And as a result of XRD analysis, in case of origin powder of non-neutralized paste, CaO peak is found at $700^{\circ}C$. but, heat temperature to generate CaO would increase when the content of neutralized ingredients is increased. Finally, recycle cement heated at $700^{\circ}C$ 120min. shows the best compressive strength when the content of neutralized ingredients in recycle cement is less then 50%.

• KCI Concrete Journal
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• v.11 no.3
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• pp.127-140
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• 1999

In this paper, a microscopic analysis of prefinitelv strained cement paste specimen was carried out. The microscopic behavior of concrete under triaxial stress must be fully understood in order to explain the additional ductilitv that comes from lateral confinement and to get microstructural information in large deformed and large strained concrete. The so-called "tube-squash" test was applied to achieve enormously high shear and deviatoric strain of concrete under extremly high pressure without fracture. Then, microscopic analyses by focusing on hydration and microstructure of Prefinitely strained cement paste were carried out on cored-out deformed and virgin (undeformed) cement paste specimens : the first specimen being 40 days old, the second one being one year old. The microscopic analysis bv Field Emission Scanning Electronic Microscope (FESEM) was carried out for comparison between the specimens after 40 days and those arter one year. For one year old specimens, X-Ray Diffractometer (XRD) analysis, Energy Dispersive x-rav Spectrometer (EDS) analysis, and Differential Thermal Analysis/Thermo-Gravitv (DTA/TG) analysis were also carried out to study the hydration and the microstructures of prefinitely strained cement paste specimen by focusing on the methodologies of their microscopic analyses. analyses.

• Computers and Concrete
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• v.11 no.4
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• pp.271-289
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• 2013

In this research, a developed microstructural model of cement particles was presented to describe the cement hydration procedure. To simplify the hydration process, the whole hydration was analyzed in a series of sub-steps. In each step, the hydration degree, as well as the microstructural size of the hydration cell, was calculated as a function of the radius of the unreacted cement particles. With the consideration of the water consumption and the reduction of the interfacial area between water and hydration products, the micro-level expressions of the cement hydration kinetics were established. Then the heat released and temperature history of the concrete was carried out with the hydration degree obtained from each sub-steps. The equivalent age method based on the Arrhenius law was introduced in this research. Based on the equivalent age method, a maturity model was applied to describe the evolution of the mechanical properties of the material during the hydration process. The finite element program ANSYS was used to analyze the temperature field in concrete structures. Then thermal stress field was calculated using the elasticity modulus obtained from code formulate. And the risk of thermal cracking was estimated by the comparison of thermal stress and concrete tensile strength.

• Proceedings of the Korea Concrete Institute Conference
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• 1998.10c
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• pp.185-190
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• 1998

Corrosion of steel reinforcement is the most significant factor of deterioration in reinforced concrete structures. Chloride ion is considered one of the most common culprits on the corrosion of steels in concrete. The main objective of this study is understanding behavior of chloride ion in hardened cement pastes at different stages of curing. Cement pastes with water-cement ratio of 0.5 are allowed to hydrate in sealed containers for 28, 70, 180 days. And than pore solution is expressed. It was found that the $Cl^-$ concentrations in pore solution is decreased with increasing curing time in all Nacl addition level, the $OH^-$ concentrations is increased to 70 days but decrease at 180 days in all Nacl addition level. The $Cl^-$/$OH^-$ in pore solution is increased with increasing curing time in all Nacl addition level, however $Cl^-$/$OH^-$ of maximum Nacl addition level(Nacl 0.54% by weight of cement) is under the onset of depassivation level 0.3.

• Proceedings of the Korea Concrete Institute Conference
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• 2001.11a
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• pp.549-554
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• 2001

It is possible for concrete using sea sand to contain chloride ion as well as cation such as Na$^{+}$and $K^{+}$ during mixing process. It is known that some cations such as Na$^{+}$and $K^{+}$ remain in pore solution without binding In this study, therefore, we intend to inspect the behavior of cations in cement paste as well as NaCl, CaCl$_2$ and KCI through analysis of pore solution extracted from cement paste with high pressure vessel. As a result, increase of alkali ions by adding sea sand and admixtures to the fresh concrete means use of the cement contained high alkali contents. In this case, alkali ions in pore solution can decrease durability of cement products causing alkali-aggregate reaction or accelerated carbonation. So it needs to be studied.studied.

• Journal of The Korean Society of Agricultural Engineers
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• v.46 no.4
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• pp.49-55
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• 2004

Properties of concrete using low heat portland cement is different from using ordinary portland cement and temperature of aggregate can be expected to have an important influence on its properties. In this study, experiment by setting up 5 levels (40, 30, 20, 4, $-2^{\circ}C$) by temperature of aggregate for evaluation properties of concrete using low heat portland cement was conducted. The experiments include slump test, air content test, change of slump, change of air content and compressive strength of concrete test. As the result of experiments, slump and air content was decreased by increasing temperature of aggregate. But it was not exceeding it's limit. Change of slump and air content was rapidly decrease by decreasing temperature of aggregate. At early age, compressive strength was influenced by the temperature of aggregate.

• Proceedings of the Korea Concrete Institute Conference
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• 1999.04a
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• pp.437-442
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• 1999

Corrosion of steel reinforcment is the most significant factor of deterioration in reinforced concrete structures. Chloride ion is considered one of the most common culprits on the corrosion of steels in concrete. This study is effect of cement hydraulic degree on the chloride binding in hardened cement pastes. With increasing the cement hydration, cement products such as CSH and Ca(OH)2 were increased, and the part of added chloride were binded with them. With respect to A type, in first, the additional contents of chloride of 27.08mM/L in pore solution were reduced as 4.3mM/L at 3 days, 4.0mM/L at 7 days, 3.6mM/L at 28 days.