• Journal of the Korean Ceramic Society
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• v.52 no.1
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• pp.28-32
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• 2015

In this article, the influence of a hydrolyzed wheat protein retarder on the hydration process, ion concentration in liquid phase, degree of supersaturation, and crystal morphology of plaster was investigated. Furthermore, the retarding mechanism and the strength loss of gypsum were also studied by scanning electron microscopy (SEM). The results indicate that the use of the hydrolyzed wheat protein retarder for plaster achieved a better retarding effect and lower strength loss. The combination of gypsum plaster with the retarder not only decreased the plaster's early hydration rate and prolonged its setting time efficiently, but also militated against the crystal morphology of dihydrate gypsum. For example, the crystal dimensions changed little, but the proportion of needle-shaped crystals decreased. Combination with calcium ions on the surface of dihydrate gypsum crystal nuclei may form a chemisorbed layer, reduce the surface energy of the crystal nuclei, and inhibit the growth of the crystal nuclei of dihydrate gypsum. Consequently, the hydration process of building gypsum becomes greatly extended and is slowed down significantly.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2014.05a
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• pp.222-223
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• 2014

In this study, industrial by-products including blast furnace slag, incineration ash and waste gypsum were used with recycled fine aggregates to manufacture the zero-cement mortar.The replacement ratio of dihydrate gypsum and anhydrite gypsum was fixed as 0 and 10%, the replacement ratio fo WA1 was fixed as 0.5% and 1.0%, respectively. It could be identified that when the replacement of gypsum was 10% and WA1 of 1.0%, the strength could be in the range of normal strength.

• Resources Recycling
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• v.30 no.1
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• pp.83-91
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• 2021

Ladle furnace slag is a byproduct of the steel-making process, and it contains the mineral β-C2Sandtherapid-settingmineral (dependingonwhichreducingagenthasbeenused). Ladle furnace slag is often treated through slow cooling, which causes the slag to lose its reactivity. In this study, the properties of air-quenched CAC and pulverized ladle furnace slag containing gypsum were evaluated, and the optimal mixing ratio was determined for broadening their usage. Consequently, the properties of CAC aredemonstrated by the dissolution of gypsum after a period of three hours and the content of gypsum after a period of one day. The optimal mixing ratio of anhydrate and hemihydrate gypsum is found to be within 30% and that of dihydrate gypsum is found to be higher than 35%. Furthermore, based on the results of CAC with dihydrate gypsum, the applicability of the by-product dihydrate gypsum has been verified.

• Resources Recycling
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• v.24 no.1
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• pp.12-20
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• 2015

In this study, change of hydration property with contents and type of gypsum in ternary natural hydraulic lime containing blast furnace slag and gypsum was investigated. Anhydrite, hemihydrate and dihydrate were added 3 % and 10 %, respectively in natural hydraulic lime adding blast furnace slag 20 %. Hydration and physical behavior due to solubility and reactivity of different types of gypsum were analyzed in early hydration. As a result of analysis of hydration properties, in all samples, hydrates such as ettringite and C-S-H were produced in early hydration, and amount of hydrates with increase of hydration time was increased. In the case of compressive strength, when contents of gypsum are 3 %, it was higher compressive strength than other specimens. At hydration 28 days, for addition of anhydrite and hemihydrate, compressive strength was more than adding dihydrate.

• 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.

• Journal of the Korean Recycled Construction Resources Institute
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• v.7 no.1
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• pp.74-81
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• 2019

In this study, to characterize the application of CSA and dihydrate gypsum Utilizing industrial byproducts, we investigated the characteristics of CSA and dihydrate gypsum to investigate the characteristics of Mine Liner according to the addition amount. As a result of compressive strength, length change and absorption rate of mining lime wastewater according to CSA addition amount, up to 30% of CSA showed a positive effect on shrinkage and absorption reduction effect as well as strength at initial age. However, due to excessive use of CSA 50%, it was reduced by 15% compared to OPC due to increase of absorption rate and decrease of cement amount due to over expansion rather than shrinkage compensation and void filling.

• Journal of the Korean Recycled Construction Resources Institute
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• v.8 no.1
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• pp.8-16
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• 2020

As the circulating fluidized bed combustor(CFBC) boilers system to generate electric power increase in order to reduce environmental pollution, a lot of CFBC fly ashes(CFFA) are produced. CFFA has limited use in concrete because it contains free CaO, which can cause cement expansion and rapid initial hydration. In this study, the microstructure and the initial development of compressive strength characteristics were experimentally analyzed to be used as a stimulant to replace natural gypsum by mixing with CFFA and phosphate gypsum to enhance the initial strength of portland blast furnace slag cement. The recycled gypsum was used as flue-gas desulfurization gypsum and phosphate gypsum. Experimental results show that the initial strength development is relatively lower when CFFA and dihydrate gypsum are mixed, but the strength improvement effect of the mixture with CFFA and anhydrous gypsum as an anhydritedII typed crystalized gypsum is similar to that of natural gypsum. As a result, it w as analyzed to have high possibility of use for stimulant of portland blast furnace slag cement.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2013.11a
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• pp.137-138
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• 2013

Nowadays, research about using recycled aggregate as alkali activator has been investigated. By the mechanism of Alkali activation, blast furnace slag's potential hydraulis property would be activated. Thee application of this technique is considered as fit for low strength concrete, so it's suitable in concrete secondary production such as bricks and blocks. Aside alkali activator, sulfate could also activate blast furnace slag's potential hydranlis property. In this research, gypsum(CaSO4·2H2O)has been added with blast furnace slag. Fundamental experiment such as flow and strength has been tested to evalnate effect of gypsum's activation property.

• 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 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.