• Journal of the korean academy of Pediatric Dentistry
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• v.28 no.4
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• pp.700-708
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• 2001

Traumatic injuries in young patients can result in the interruption of the development of the incompletely formed roots. In teeth with incomplete root-end formation and necrotic pulps, the root canals must be completely debrided. Because of a lack of an apical stop and the presence of thin and fragile walls in these teeth, it is imperative to perform apexification to obtain an adequate apical seal. Calcium hydroxide has become the material of choice for apexification. Despite its popularity for the apexification procedure, calcium hydroxide therapy has some inherent disadvantages that include variablility of treatment time, unpredictability of apical closure, difficulty in patient follow-up, and delayed treatment. An alternative treatment to long-term apexification procedure is the use of an artificial apical barrier that allows immediate obturation of the canal. MTA(Mineral Trioxide Aggregate) is a powder consisting of fine hydrophilic particles of tricalcium silicate, tricalcium aluminate, tricalcium oxide and silicate oxide. MTA has a pH of 12.5 after setting, similar to calcium hydroxide. This may impart some antimicrobial properties. MTA has low solubility and a radiopacity slightly eater than that of dentin. Also, MTA leaked significantly less than other materials and induced hard-tissue formation more than other materials.

• Resources Recycling
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• v.3 no.3
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• pp.27-31
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• 1994

We tested the limestone sludge produced in Pohang Iron & Steel Co., Ltd. as a filler powder for the effective use of portland cement. Hydration process was investigated by measuring the hydration rate, the amounts of non-evaporable water and compressive strength of cement-limestone sludge paste prepared by mixing limes-tone sludge with cement. The results obtained in this study can be summarized as follows: 1. There is no significant difference between the cases of adding up to 10% limestone sludge and those of unmixed cement system. However the reaction rate increases in the 5% limestone sludge system(due to the effects of fine). 2. The compressive strength increases proportionally with increasing the measured amount of non-evaporable water, Adding 5% limestone sludge also increases the strength a little higher, and the compressive strength and calcium silicate hydrates. In the case of the mixed limestone sludge, $2\theta$=$11.7^{\circ}$ peak appears in the samples of 28 days hydration. This peak indicted the presence of calcium carboaluminate hydrate. Although limestone sludge is generally regarded as a inert materials, some kinds of cement can produce a calcium carboaluminate by reacting with aluminate in cement pastes.

• Journal of the Korean Ceramic Society
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• v.49 no.5
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• pp.442-447
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• 2012

This study investigated on the early hydration and physical characteristics of BFS by pH variation. NaOH solution was used as a pH activator. In the range from pH 12 to pH 14, Experiment was compared the hydration propertied of OPC(Ordinary Portland Cement) and BFS(Blast Furnace BFS) and BFS containing 2 wt% of gypsum. It was found that CAH(Calcium Aluminate Hydrates) phases and CSH(Calcium Silicate Hydrates) phases were formed during the early hydration of BFS, and that CAH phases, CSH phases and ettringites were formed during the early hydration of BFS containing 2 wt% of gypsum. Furthermore, early hydration of BFS and BFS containing 2 wt% of gypsum were faster then OPC at pH 14, and the 1 day compressive strength of BFS increased by approximately 30% compared to OPC, and BFS containing 2 wt% of gypsum also increased by approximately 40% compared to OPC.

• 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.

• Journal of Environmental Science International
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• v.29 no.6
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• pp.605-612
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• 2020

To improve the initial strength and stability of lightweight-foamed concrete, which shows suitable sound absorption and insulation characteristics, the effect of CO₂-reduced cement on the properties of the concrete was investigated. Various mixing ratios were applied by substituting a certain amount of slag and Calcium Sulfo Aluminate (CSA) in CO₂-reduced Ordinary Portland Cement (OPC) and the physical properties of the samples were examined using the Korean Standard. The kiln temperatures of the CSA were 100-200℃ ; these values are lower than those of OPC and can lead to energy saving. In addition, the low limestone content reduces greenhouse gas emissions by 20 %. Adding a small amount of CSA in OPC content activates Ca-Al-H₂-based hydrates, and the initial compressive strength of the concrete is improved. As the CSA content increased, the thermal conductivity of the concrete decreased by up to 8% compared to plain concrete, thus indicating an improvement in its insulation. Therefore, the settlement stability was improved as the addition of CSA shortened the setting time.

• Resources Recycling
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• v.11 no.4
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• pp.27-36
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• 2002

The clinker of which main component was calcium-chloroaluminate ($l1CaOㆍ7Al_2$$O_3$ㆍ$CaCl_2$), was synthesized with the bottom ash of municipal solid waste incinerator ash. The hydration mechanism and synthesis temperature of calcium-chloro-aluminate were investigated. The synthesized clinker was blended with a cement. It was substituted with 3～13 wt.% for clinker and $CaSO_4$ of ordinary portland cement. The compressive strength and the content of leached heavy metals of its mortar were measured. Calcium-chloroaluminate was synthesized above $800^{\circ}C$ and its main hydrate was ettringite ($3CaOㆍAl_2$$O_3$ㆍ$3CaSO_4$ㆍ$32H_2$O). The calcium-chloroaluminate was also synthesized above $800^{\circ}C$ with the bottom ash of which size fraction was below 30 mesh mainly. The compressive strength of the blended cement mortar was increased as the additive content of the clinker synthesized from the bottom ash was increased by 11 wt.%. The concentration of heavy metals leached from each mortar was satisfied with the value of the environmental standards and regulations.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.7 no.1
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• pp.75-81
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• 1998

We have studied internal quality including chemical compositions, microscopic structure and nonmetallic inclusion of test materials. We have analyzed tensile strength value, hardness value, impact value etc. In analyzing internal quality, all of the test materials showed typical ferrite+pearlite structure. But nonmetallic inclusion showed oxide and sulfide inclusions in medium carbon steels, and sulfide inclusion is S-free cutting steels. In ca+ S-free cutting steels, the calcium aluminate and sulfide complex inclusion had low-melting points as deformation of sulfide and oxide inclusion is existed. It was found that tensile strength and hardness give maximum value in medium carbon steels, where as minimum in Ca + -free cutting steels. But values of elongation, reduction of area impact are reverse. Fracture surface of impact specimen is ductile in free cutting steels but brittle in medium cabon steels.

• Proceedings of the Korea Concrete Institute Conference
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• 1998.10a
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• pp.386-391
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• 1998

Recently, high performance concrete developed has a good quality at fresh and hardened state, but high binder contents results in spending much money on manufacturing and many cracks by drying and autogenous shrinkage. Therefore, in this paper, not only prevention of cracks caused by drying and autogenous shrinkage, but improvement of quality and accmplishment of economy by applying F.A(fly ash), S.F(silica fume) and CSA(calcium sulfa aluminate) expansive additives as an inorganic admixtures in W/B 35% are discussed. According to the experimental results, when 5% of CSA Expansive additives and 15:5 (F.A:S.F)are replaced at unit cement content, high performance concrete with both good compensation of drying and autogenous shrinkage at hardened state is accomplished.

• 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.17 no.4
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• pp.217-221
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• 1980

Hydration of granulated blastfurnace slag-gypsum-$C_4A_3\bar{S}$ clinker/modified converter slag clinker was investigated to develop the cement of slag-gypsum system. In the hydration of granulated slag-gypsum-$C_4A_3\bar{S}$ system clinker, the hydrates such as ettringite, CSH gel and $AH_3$ gel were formed, and the strength of hardened body would be increased by forming compact microstructure. The modified converter slag clinker which contains alite and calcium aluminate was synthesized, and the hydration reactivity of the cement from this clinker, gypsum and granulated slag is similar to usual portland cement, and the hydrates were mainly CSH, ettringite, and $Ca(OH)_2$.