• Journal of the Korean Ceramic Society
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• v.27 no.2
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• pp.195-200
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• 1990

For the development of low energy cement, the belite cement clinker of calcium sulphoaluminate ferrite type was synthesized at 130$0^{\circ}C$ and containing C2S, C4A3S as the major minerals along with C3A, C4AF, CS by using limestone, dolomite, clay, iron ore, gypsum and alumina as raw materials. At over 130$0^{\circ}C$, C4A3S was decomposed and thus C3A was increased. When hydrated, this cement was hardened, producing ettringite, CSH, etc.

• Architectural research
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• v.20 no.1
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• pp.27-34
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• 2018

To improve the chloride ingress resistance of concrete, slag is widely used as a mineral admixture in concrete industry. And currently, most of experimental investigations about non steady state diffusion tests of chloride penetration are started after four weeks standard curing of concrete. For slag blended concrete, during submerged chloride penetration tests periods, binder reaction proceeds continuously, and chloride diffusivity decreases. However, so far the dependence of chloride ingress on curing ages are not detailed considered. To address this disadvantage, this paper shows a numerical procedure to analyze simultaneously binder hydration reactions and chloride ion penetration process. First, using a slag blended cement hydration model, degree of reactions of binders, combined water, and capillary porosity of hardening blended concrete are determined. Second, the dependences of chloride diffusivity on capillary porosity of slag blended concrete are clarified. Third, by considering time dependent chloride diffusivity and surface chloride content, chloride penetration profiles in hardening concrete are calculated. The proposed prediction model is verified through chloride immersion penetration test results of concrete with different water to binder ratios and slag contents.

• Korean Journal of Metals and Materials
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• v.46 no.7
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• pp.437-442
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• 2008

The synthesis and hydration of Calcium Sulfo Aluminate[$3CaO{\cdot}3Al_2O_3{\cdot}CaSO_4(C_4A_3{\overline{S}})$, CSA cement utilizing secondary steelmaking refining slags is studied for recycling the discarded steel plant wastes to meet the environmental requrations imposed on the steel industry. Raw materials of secondary refining slag, lime sludge, gypsum and bauxite were prepared to be sintered at $1,250^{\circ}C$. The sintered samples were hydrated for 1, 3 and 7 days to evaluate the mineralogical and physico-mechanical properties. The hydration products evaluated with the aid of SEM and XRD analyses confirmed the formation and the continuing growth of ettringite phase with the further hydration times, which plays a role in developing the early strength and the expansion properties of cements. The physico-mechanical properties of hydrated CSA products employing the recycled steelmaking refining slags determined in terms of compressive strength and linear expansion of hydrated products are found to be superior to those of the Ordinary Portland Cement(OPC) or the other commercial CSA cements.

• Journal of the Korean Ceramic Society
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• v.22 no.4
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• pp.21-25
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• 1985

For studying the influence of addition of Polyvinyl alcohol (PVA)-montmorillonite complex on the hydration of Portland cement the PVA-montmorillonite derivatives were prepared in advance an characterized system-of Portland cement the PVA-montmorillonite derivatives were prepared in advance and characterized systema-tically. PVA with the polymerizationdegree ranging from 500 to 2000 have been intercalated into the lamellar structure of hydrated montmorillonites which were fractionated under 2㎛ by Stock's rule. In all cases the constant basal spacing of ∼20Å was determined whatever the molecular weight of PVA used. And the carbon chain orientation of PVA in the interfoliar space has been deduced to be parallel with bilayer structure.

• Journal of the Korea Institute of Building Construction
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• v.21 no.4
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• pp.269-279
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• 2021

Palm Oil Fuel Ash(POFA) has been widely used to replace Portland cement to enhance the mechanical properties and durability of concrete. However, it reduces the workability of concrete due to the high content of unburnt carbon and its angular shape requiring the usage of superplasticizer to ensure a proper flowability. In this study, effects of different types and dosage of superplasticizer on the early mechanical and hydration properties of cement paste containing micro-POFA were evaluated using mini-slump test, early compressive strength, TGA, XRD, and SEM. The results indicated that the flowability of cement paste containing micro-POFA reduced as the replacement ratio of micro-POFA increased. As the dosage of superplasticizer increased, the flowability was also increased. In addition, the usage of superplasticizer reduced the early compressive strength, and the strength decreased with an increase in the dosage of superplasticizer. It was confirmed that superplasticizer hindered the formation of C-S-H leading to a relative increase in the formation of Ca(OH)₂.

• Journal of the Korea Concrete Institute
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• v.17 no.6 s.90
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• pp.1019-1024
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• 2005

To research effects of various chemical superplasticizers(Lignosulfonic acid, Naphthalene sulfonated formaldehyde condensate, melamine sulfonated formaldehyde condensate, and Polycarboxylate) on the hydration of cement, experiments involving XRD, SEM, and DSC have been analysed with cement paste specimens. Regardless of types and dosages of superplasticizers, hydration reaction of specimen applied superplasticizer was delayed to 3 day, but then it showed similarity to plain which don't add superplasticizer. Moreover, the hydrating rate of cement paste was retarded as dosage of superplasticizer was increased. Also, kinetics related with hydrate of cement paste was slow in order of lignosulfonic acid, polycarboxylate, melamine and naphthalene sulfonated formaldehyde condensate. Nevertheless, when all kinds of chemical admixtures were used, morphologies of these hydrates were denser and more uniform than those of plain.

• Proceedings of the Korea Concrete Institute Conference
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• 1999.10a
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• pp.823-828
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• 1999

Blast furnace slag cement(BSC) has many merits in relation to its prodution cost or environmental problem of these days, but it has still some limitation in broad use mainly because it has the lower early hydration strength than the normal portland cement(PC) has. In the present study, several different experimental concepts to improve its low strength in the early hydration stage were tried out which addition of the effective alkali activators such as Ca(OH)2 and limestone powder, fly ash in existing BSC. It was found that the addition of suitable quantity the effective alkali activators such as Ca(OH)2 and limestone powder, fly ash in BSC can be a possible way to get enough early strength compared with the PC and existing BSC.

• Journal of the Korea institute for structural maintenance and inspection
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• v.26 no.4
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• pp.48-56
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• 2022

Controlling the setting time of cementitious materials is one of the most important factors in securing early-age performance of concrete structures. Recently, the use of retarding admixtures, which enable the inhibition of some hydration products to control the securing time due to average temperature rise is suggested. Although various non-destructive evaluation methods have been proposed to evaluate cement hydration and hardening of cement-based materials to overcome the limitations of Vicat needle test, experimental research is still required to use the non-destructive evaluation method with added retarding admixtures. In this study, measurements of electrical resistivity and ultrasonic wave velocity in early-aged cement pastes were performed according to the addition of retarding admixture(tartaric acid). The setting time of the cement pastes was evaluated by obtained rising time of the both non-destructive measurements. As a result, the possibility of evaluating the setting delay in cement pastes was confirmed through comparative analysis with the initial and final setting times by Vicat test. In addition, X-ray diffraction results at the rising time of electrical resistivity showed a key hydration product affecting the setting delay.

• Proceedings of the Korea Concrete Institute Conference
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• 2004.11a
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• pp.305-308
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• 2004

Cold weather concrete is the concrete which is used during construction under low-temperature' environment, and this kind of concrete has to be taken care not to be frozen in early ages of setting-hardening, It is specified in the Concrete Standard Specification(2003) as 'the cold weather concrete must be used on the weather condition under the average daily outdoor temperature below $4^{\circ}C$.' In this research, the mechanical characteristics and hydration heat on the cold weather concrete using high early strength portland cement were studied. As a result, the excellent quality was obtained and high early strength portland cement is expected to be used widely as the cold weather concrete.

• International Journal of Concrete Structures and Materials
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• v.9 no.4
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• pp.391-399
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• 2015

This study modeled the compressive strength and elastic modulus of hardened cement that had been treated with an expansive additive to reduce shrinkage, in order to determine the mechanical properties of the material. In hardened cement paste with an expansive additive, hydrates are generated as a result of the hydration between the cement and expansive additive. These hydrates then fill up the pores in the hardened cement. Consequently, a dense, compact structure is formed through the contact between the particles of the expansive additive and the cement, which leads to the manifestation of the strength and elastic modulus. Hence, in this study, the compressive strength and elastic modulus were modeled based on the concept of the mutual contact area of the particles, taking into consideration the extent of the cohesion between particles and the structure formation by the particles. The compressive strength of the material was modeled by considering the relationship between the porosity and the distributional probability of the weakest points, i.e., points that could lead to fracture, in the continuum. The approach used for modeling the elastic modulus considered the pore structure between the particles, which are responsible for transmitting the tensile force, along with the state of compaction of the hydration products, as described by the coefficient of the effective radius. The results of an experimental verification of the model showed that the values predicted by the model correlated closely with the experimental values.