• Advances in concrete construction
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• v.11 no.3
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• pp.183-192
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• 2021

Due to economic and environmental benefits, increasing the substitution ratio of ordinary cement by industry by-products like fly ash (FA) is one of the best approaches to reduce the impact of the concrete industry on the environment. However, as the substitution rate of FA increases, it will have an adverse impact on the performance of cement-based materials, so the actual substitution rate of FA is limited to around 10-30%. Therefore, in order to increase the early-age strength of high replacement (30-70%) low-calcium ultrafine FA blended cement paste, sodium sulfate and calcium sulfate dihydrate were used to improve the reactivity of FA. The results show that sodium sulfate has a significant enhancement effect on the strength of the composite pastes in the early and late ages, while calcium sulfate dihydrate has only a slight effect in the late ages. The addition of sodium sulfate in the cement-FA blended system can enhance the gain rate of non-evaporation water, and can decrease the Ca(OH)2 content. In addition, when the sulfate chemical activators are added, the ettringite content increases, and the surface of the FA is dissolved and hydrated.

• Journal of the Korea Institute of Building Construction
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• v.14 no.3
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• pp.252-258
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• 2014

With the vision of 'a low carbon green develop' various industrial by-products were used as replacement of cement, in order to reduce $CO_2$ emissions from the manufacturing process of cement. Blast furnace slag is one of the industrial by-products. Due to the similar chemical compositions to ordinary Portland cement, blast furnace slag have been widely used in concrete with minimum side effects. Hence, in recent years, alkali activated slag-based composites are extensively studied by many researchers. However, the alkali activator can cause a number of problems in practice. Therefore, in this study, an alternative way of activating the slag was investigated. To activate the slag without using an alkali activator, calcium sulfate dihydrate was chosen and mixed with natural recycled fine aggregate. Fundamental properties of the slag-based mortar were tested to evaluate the effect of calcium sulfate dihydrate.

• Proceedings of the Materials Research Society of Korea Conference
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• 2009.05a
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• pp.45.1-45.1
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• 2009

In this study, we investigated a calcium phosphate-calcium sulfate injectable bone substitute (IBS) with organic reinforcement of chitosan, citric acid and hydroxypropyl-methyl-cellulose (HPMC). The powder component of IBS consisted of tetra calcium phosphate (TTCP), dicalcium phosphate dihydrate (DCPD) and calcium sulfate dihydrate (CSD). The liquid component was a solution of citric acid and chitosan. The effect of HPMC in terms of setting time, compressive strength and apatite forming ability on this IBS was investigated. The mass content of HPMC in liquid phase was varied in array of 0%, 2%, 3% and 4%. The setting times obtained between 20 and 45 minutes. Compressive strength was achieved over 20 MPa after incubation at 370C and in 100% humidity for 28 days. Porosities were evaluated in relation with compressive strength. Elastic moduli of the 28 days after-incubation IBS were obtained around 4GPa

• Journal of the Korea Furniture Society
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• v.19 no.1
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• pp.83-90
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• 2008

Gypsum-wood composites were made by introducing inorganic substances into wood using calcium chloride, first treating solution, and sodium sulfate, secondary treating solution, by double diffusion process under atmospheric pressure at room temperature. The process conducted as follows: water saturated specimens were soaked in calcium chloride solutions at several concentration. Then the specimens were soaked further in saturated sodium sulfate solution, and they were leached in flowing tap water for 24h. To attain sufficient weight percent gain (WPG) values, the suitable concentration of calcium chloride and soaking time in saturated sodium sulfate solution were 20% and 48h, respectively. Inorganic substances were produced mainly in the lumina of tracheides. It was made sure that these substances were dihydrate gypsum($CaSO_4$ $2H_2O$) by X -ray microanalysis (SEM-EDX). The composites had good fire resistance due to low heat transfer rate of gypsum formed in wood. However, the composites had little decay resistances, because they showed high weight losses by test fungi attacks.

• Horticultural Science & Technology
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• v.28 no.6
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• pp.1072-1077
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• 2010

Plant diseases including gray mold caused by Botrytis cinerea are often reduced when calcium compounds are used as alternative materials in paprika. However, much less information is available about the effects of calcium compounds on controlling of $B.$ $cinerea$. Seven calcium compounds such as calcium sulfate dihydrate, calcium chloride, calcium nitrate, calcium oxide, calcium hydroxide, calcium carbonate, and calcium hydride were evaluated for their effectiveness against $B.$ $cinerea$ on potato dextrose agar medium. The pH of selected calcium compounds was higher (pH 8.2-10) than that of the control (pH 6.6). Calcium carbonate, calcium oxide, calcium hydride, and calcium hydroxide among seven calcium compounds were more effectively inhibited the growth of $B.$ $cinerea$ than other calcium compounds. In the case of spraying the spore suspension on paprika applied with the selected four calcium compounds and supplied with the selected calcium supplements in a hydroponic culture system, the paprika treated with calcium compounds showed less severity of disease than those untreated plants. On the basis of our results, we propose that the suppressive effects of calcium compounds on $B.$ $cinerea$ in paprika resulted from the supply of calcium and a certain degree of salt stress.

• Proceedings of the Korean Institute of Resources Recycling Conference
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• 2005.05a
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• pp.237-241
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• 2005

• Proceedings of the IEEK Conference
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• 2001.10a
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• pp.432-436
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• 2001

In this study, calcium sulfate(gypsum) powder was obtained using waste sulfuric acid and stainless refinery sludge by- produced from chemical reagent and the iron industry, by the neutralization of waste sulfuric acid. As variables for the experiment the mole ratio of the H$_2$SO$_4$ : Ca(OH)$_2$, the pH, the reaction temperature and time, the amount of catalyst were used. The crystal shape and microstructure of obtained powder were observed by XRD and SEM, and the thermal property was investigated by DTA. As the NaCl is added 0~20wt% as a catalyst to the H$_2$SO$_4$ : Ca(OH)$_2$, system it can be found that the crystal shape goes through the processes as follows : gypsum dihydratlongrightarrowgypsum hemihydrate＋gypsum dihydratelongrightarrowgypsum hemihydrate. And gypsum hemihydrate is $\beta$-type as the result of DTA. As waste sulfuric acid and stainless refinery sludge were used, the pH of reacted solution (which was 0.8) was rapidly raised up to 8~9 by the addition of stainless sludge and gypsum dihydrate was produced as a by-product. Therefore, it was found that stainless refinery sludge is sufficiently applicable for the neutralization of waste sulfuric acid.

• Journal of the Korean Ceramic Society
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• v.34 no.8
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• pp.861-869
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• 1997

In order to investigate the reaction in the system of anhydrite II-blast furnace slag, the paste hydration which made up with a liquid/solid ratio of 0.45 for 1, 3, 7, 14, 28days by the addition of accelerators to 10~30wt.% slag with natural gypsum calcined for 1hour at 500/$700^{\circ}C$ was studied by combined water determination, XRD, DTA, DSC and SEM. As a result of this experiment, it was found that hydration rate was faster in the system calcined at 50$0^{\circ}C$. Therefore the anhydrite was converted to calcium sulfate dihydrate in the hydration for 1day but the slag was not almost reacted. For the gypsum calcined at $700^{\circ}C$, the hydraton rate in the system of K2SO4 addition was faster than others in the earier period, but the activated effect of the system of Al2(SO4)3 addition was regarded as the highest over 3days. As the amount of slag was increased, they dydration rate was delayed and ettringite was observed in the case of K2SO4 system. However both Al2(SO4)3 and AlK(SO4)2 systems showed calcium sulfate dhydrate only as hydrated products.

• Analytical Science and Technology
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• v.13 no.2
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• pp.158-165
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• 2000

The purity of gypsum and quantitation of impurities of flue gas gypsum will not only play an important role in deciding of the optimal condition during a trial run of FGD (flue gas desulfurization), but also can be utilized in quality control of gypsum. The purity of gypsum can be determined from combined water, sulfur trioxide and calcium concentration. We found that the thermal analysis by TGA (thermogravimetric analysis) was the most accurate and convenient method to determine the purity of gypsum. This method will be done in a hour and the results were reproducible. On the other hand, the best way of the analysis of impurities in gypsum was fusion method using $LiBO_2$ as a fusion agent. We also determined the amount of $CO_2$ gas to analyze magnesium carbonate and calcium carbonate contents. The analyses of combined water by TGA, fusion method followed by ICP-AES (inductively coupled plasmaatomic emission spectroscopy) and determination of $CO_2$ amount can lead to more accurate and convenient method for gypsum analysis.

• Resources Recycling
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• v.15 no.3 s.71
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• pp.20-29
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• 2006

This study was carried out for to recover the purified crystalline gypsum from phosphogypsum by means of using it's crystallographical Properties. The dehydration of hydrated phosphogypsum to $\alpha$-hemihydrate is completed with the 2 hours treatment of it in $99^{\circ}C$ waterrs. The purified crystalline gypsum having the maximum size of $200{\mu}m$ was obtained by 325# wet screening after recrystallization of the $\alpha$-hemihydrate gypsum at the condition of $Na_2SO_4$ 10 wt%, slurry density 20%, $pH\;5{\sim}6,\;65^{\circ}C$ and 4hr. In this process, the yield of gypsum was 93.9% and its grade was 99%.