• Journal of the Korean Ceramic Society
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• v.26 no.5
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• pp.698-704
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• 1989

Basic investigation for the flexural strength and water stability of hardened cement pastes using ordinary portland cement with water-soluble polyer (hydroxypropyl methyl cellulose ; HPMC) was carried out with 0.2 of water cement ratio. For molding of the specimen, the paste was mixed by twin roll mill. According to increase in the content of HPMC, the setting time of cement paste was delayed and the flexural strength was increased. The maximum flexural strength of hardened cement paste with 5.0wt% of HPMC was about 330 kg/$\textrm{cm}^2$. The expansion of the hardened cement paste immersed in water was increased with the content of water soluble polymer(HPMC). Consequently, the strength and the water stability of the hardened cement pastes were remarkably reduced by the expansion of them.

• Journal of the Korean Ceramic Society
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• v.27 no.4
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• pp.495-500
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• 1990

Investigation for the preparation of high strength hardened cement paste using ordinary portland cement, hydroxypropyl methyl cellulose (HPMC) with admixtures was carried out. For molding of the specimen, the paste was mixed with 0.1 of water cement ratio by twin roll mill. The maximum flexural strength of dried hardened cement paste was about 600∼700kg/㎠. When the SiC was added to the paste, the dry flexural strength was about 920kg/㎠ and the young's modulus was 5.2×105kg/㎠. When the admixtures were added to the specimens, wet strength of the harened cement paste immersed in water was showed around 50∼100kg/㎠ higher than that of plain specimen. Consequently it is recognized the water stability of hardened cement paste was remarkably improved by adequate admixture.

• Journal of the Korean Ceramic Society
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• v.24 no.4
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• pp.329-334
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• 1987

Diffusion of SO4-- ion in hardened cement paste with slag and siliceous powders such as silica fume and white carbon was investigated. Ca(OH)2 from hardenend cement paste was dissolved by sea-water and then gypsum was formed from the reaction of Ca++ in hardenend cement paste and SO4-- ions in MgSO4 solution. A part of the gypsum by reaction with calcium aluminate hydrates formed ettringite. Amounts of SO4-- ions passed through hardened cement paste was less than that of Cl- ions(Dcl-) in hardened cement paste were 0.1∼0.6${\times}$10-11$\textrm{cm}^2$/sec and 1∼4${\times}$10-8$\textrm{cm}^2$/sec respectively.

• Journal of the Korean Ceramic Society
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• v.24 no.3
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• pp.282-288
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• 1987

Diffusion of Cl- ion in hardened cement paste with slag and siliceous powder such as silica fume and white carbon was investigated. The addition of admixtures reduces the content of Ca(OH)2, which is the main cause of pore formation by corrosive action of sea-water. The addition of admixtures makes the hardened cement paste dense, thereby restricting the diffusion of Cl- ion and improving the resistance to sea-water. Apparence diffusion coefficient of Cl- ion in hardened ordinary portland cement paste was 3.7${\times}$10-8$\textrm{cm}^2$/sec, while that for the hardened cement paste with the admixture was 1.2∼3.2${\times}$10-8$\textrm{cm}^2$/sec.

• Proceedings of the Korea Concrete Institute Conference
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• 1997.10a
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• pp.131-136
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• 1997

It is well known that concrete is typical porous material. We pay attention to Hansen's idea that concrete may be expected to act as semi-permeable membrane, and report the effect of concentration of solution and temperature on water flux in forward osmosis. In order to measuring volume of water flux from distilled water to solution of sodium chloride through hardened cement paste, specially designed apparatus was constructed, and the following result were obtained: (1) hardened cement paste acts as semi-permeable membrane, consequently, water flux in forward osmosis may occur. (2) Rate of water flux is proportion to concentration of dilute solution, and this suggests hardened cement paste is agreeable to the theory of membrane. (3) Effect of temperature on water flux is agreeable to Arrehenius equation and is great.

• Journal of the Korean Ceramic Society
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• v.27 no.7
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• pp.861-868
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• 1990

Investigation for the preparation of high strength hardened cement paste using ordinary portland cement, hydroxypropyl methyl cellulose(HPMC) with SiC powder was carried out. The cement paste was mixed with 0.1 of water cement ratio by twin roll mill and cured 60 days in humidity chamber. The hydration degree of cement paste cured with W/C=0.1 in 60 days was about 30% and most pores in the paste were found to be existed as gel pores of diameter less than 0.01㎛. The maximum flexural strength of hardened cement paste was about 960kg/㎠. When the SiC powder was added to the paste, the flexural strength was 1000∼1100kg/㎠ and the Young's modulus was 8∼9×105kg/㎠.

• Proceedings of the Korea Concrete Institute Conference
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• 1999.04a
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• pp.160-165
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• 1999

Osmotic pressure induced by semi-permeability of hardened cement pasts and cement mortar was studied, which was considered to be a cause of failure such as separation and blistering of floor coatings or wall coatings from the concrete substrate. The specimens with a water cement ratio of 45, 60 and 75% were installed between the solution of sodium chloride and distilled water. First, we measured water flux from distilled water to sodium chloride and the ion flux of Na+ and Cl- through the specimens. Then, we measured osmotic pressure induced by semi-permeability of the specimens using an apparatus which was specially developed for this study. It was made clear that hardened cement paste and cement mortar have properties of semipermeability, and the osmotic pressure is closely related to their water cement ratio. Finally, we calculated the osmotic pressure according to Staverman's equation, which was obtained for organic membranes, and tried to explain quantitatively the observed pressure.

• Journal of the Korean Ceramic Society
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• v.27 no.8
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• pp.1034-1042
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• 1990

Investigation for the preparation of high strength hardened cement paste using ordinary portland cement, hydroxypropyl methyl cellulose(HPMC) with various admixtures was carried out. The cement paste was mixed with 0.1 of water cement ratio by twin roll mill and cured 60 days in humidity chamber. When the quartz powder or white cement was added to the paste, the flexural strength was 900∼1000kg/㎠ and the Young's modulus was 8∼9×105kg/㎠. When the silicafume was added, the flexural strength was 800kg/㎠ and the Young's modulus was 6×105kg/㎠.

• Journal of the Korean Ceramic Society
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• v.27 no.5
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• pp.589-596
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• 1990

In this study, the freezing and thawing resistance in sea-water of hardened cement paste was investigated by adding slag, diatomaceous earth and fly ash as blending materials and air entraining agent and superplasticizer as admixtures to the cement paste. The structure of hardened cement pate was densified by potential hydraulic properties and pozzolan reactivities of materials and the freezing and thawing resistance of the paste was improved with the effect blending materials and admixtures. As the blending materials were added to the paste, the quantity of C3A was relatively reduced and the formation of expansive ettringite was suppressed to decrease the penetration of sea-water or Cl-, SO42-ion, and then freeze-thaw resistance was enhanced. Particulary, when 40% of slag was mixed, the resistance was excellent.

• Advances in concrete construction
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• v.5 no.3
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• pp.289-301
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• 2017

The synergistic interactions of supplementary cementitious materials (SCMs) with ordinary portland cement (OPC) in multi-blended systems could enhance the mechanical and durability properties of concrete and increase the amount of cement that can be replaced. In this study, the characteristics of the hydration products as well as paste microstructure of blended cement containing 20% coal fly ash, 10% rice hull ash and 10% sugar mill lime sludge in quaternary blended system was investigated. Portlandite content, hydration products, compressive strength, pore size distribution and microstructural architecture of hydrated blended cement pastes were examined. The quaternary blended cement paste showed lower compressive strength, reduced amount of Portlandite phases, and higher porosity compared to plain hardened cement paste. The interaction of SCMs with OPC influenced the hydration products, resulting to the formation of ettringite and monocarboaluminate phases. The blended cement paste also showed extensive calcium silicate hydrates and calcium aluminate silicate hydrates but unrefined compared to plain cement paste. In overall, the expected synergistic reaction was significantly hindered due to the low quality of supplementary cementitious materials used. Hence, pre-treatments of SCMs must be considered to enhance their reactivity as good quality SCMs can become limited in the future.