• Proceedings of the Korean Institute of Building Construction Conference
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• 2017.05a
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• pp.18-19
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• 2017

In this study, hardening characteristics and microstructure of blast furnace slag-cement mortar replaced alpha-calcium sulfate hemihydrate were analyzed. As a result of replacing alpha-calcium sulfate hemihydrate with 0, 10, 20, 30%, it was confirmed that the initial and final setting times are faster than that of blast furnace slag-cement mortar. The compressive strength of the specimens containing alpha-calcium sulfate hemihydrate decreased in the range of 42 ~ 76% at age 28 days compared with blast furnace slag-cement mortar. In the case of replacing the alpha-calcium sulfate hemihydrate, the shrinkage did not occur more rapidly than the cement mortar, but the slope of the strain curve showed a linear behavior. The results of scanning electron microscopy images analysis showed that the formation of ettringite was increased at alpha-calcium sulfate hemihydrate replaced mortar.

• Journal of the Korea institute for structural maintenance and inspection
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• v.21 no.5
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• pp.117-124
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• 2017

In this study, to evaluate the setting time, compressive strength and drying shrinkage of ordinary Portland cement and Portland blast-furnace slag cement mortar with 0, 10, 20, 30 wt.% alpha-calcium sulfate hemihydrate. As a results, as the replacement ratio of alpha-calcium sulfate hemihydrate increased, the initial setting time of ordinary Portland cement and Portland blast-furnace slag cement mortar was faster. In addition, the compressive strength decreased with increasing replacement ratio of alpha-calcium sulfate hemihydrate in both ordinary Portland cement mortar and Portland blast-furnace slag cement mortar. The strength development of Portland blast-furnace slag cement mortar with alpha-calcium sulfate hemihydrate was effective than that of ordinary Portland cement mortar. On the other hand, in the case of the mortar with alpha-calcium sulfate hemihydrate, it was confirmed that shrinkage deformation was reduced at the early age by growth pressure of needle-shaped ettringite crystals produced by incorporation of alpha-calcium sulfate hemihydrate. However, the effect of inhibiting shrinkage deformation of mortar with alpha-calcium sulfate hemihydrate was not significant as the age passed. Therefore, it is considered that the alpha-calcium sulfate hemihydrate is useful as a construction material.

• Journal of the Korea Institute of Building Construction
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• v.19 no.1
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• pp.1-7
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• 2019

This study evaluated the mechanical properties of the alpha-calcium sulfate hemihydrate replaced concrete to reduce the cracking in a box culvert power transmission. After setting the replacement ratio of alpha-calcium sulfate hemihydrate at 0, 6, 9, 12, and 15%, the setting time, compressive strength, and drying shrinkage were measured and the microstructure and crystal structure were analyzed. As a result, it was confirmed that as the replacement ratio of alpha-calcium sulfate hemihydrate increased, the setting time decreased and the compressive strength declined. On the other hand, when the alpha-calcium sulfate hemihydrate was set with 15% of replacement ratio, about 60% reduction in the drying shrinkage was shown compared to that of ordinary Portland cement. Therefore, it is thought that when the concrete replacing the alpha-calcium sulfate hemihydrate is applied to a box culvert power transmission, the cracking reduction performance will be improved, and the improvement of compressive strength will be required.

• Journal of the Korean Ceramic Society
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• v.25 no.5
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• pp.449-454
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• 1988

The effects of salts which was used as a catalysis in formation of $\alpha$-calciumusulfate hemihydrate from dicalcium sulfate hydrate were investigated on the hydration of $\alpha$-calciumsulfate hemihydrate. The hydration of $\alpha$-calciumsulfate hemihydrate was studied by the measurements of crystalline water, heat evolution. Also the hydrates were analyzed by XRD, DSC and SEM. The promotive effect each salts on the hydration was as follows: NaCl>NH4Cl>NaNO3>NH4NO3, and the hydration rate was accelerated with concentration of salts. The effect of Al2(SO4)3 and potassium sodium tartrate on the hydration was slmilar to water, whereas sodium succinate and gelatin retarded the hydration in comparision with water. These salts affected the hydration time but total heat evoution was similar.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2011.11a
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• pp.109-110
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• 2011

Gypsum is an important building material used to provide fire resistance to constructions by reducing their temperature rises. As the hardened gypsum is exposed to fire, evaporation of both the free water and the chemical bond water is easier than that in the cement extruding panel. The purpose of this study is to investigate the utilizability of alpha-hemihydrate gypsum to prevent spalling failure of cement extruding panel exposed to fire. This paper reports the fire-resistance property of a controled general cement extruding panel(C100), and gypsum-cement extruding panels(C50A50, A100) according to replacement ratio of alpha-hemihydrate gypsum. As a results, it is found that A100 and C50A50 are more effective to prevent the explosive spalling failure under standard fire condition than C100.

• Journal of the Korean Ceramic Society
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• v.24 no.4
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• pp.343-348
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• 1987

The effects of salts such as aluminum sulfate as inorganic salt(2-4%), and sodium salts of citrate, tartrate, succinate, potassium tartrate and gelatin as organic salts(0.1%) on the formation of ${\alpha}$-calcium sulfate hemihydrate from by-product gypsum of phosphoric acid process under hydrothermal condition at 123$^{\circ}C$ and 133$^{\circ}C$ were investigated. Aluminum sulfate solution exhibited the catalystic effected on the crystallization of ${\alpha}$-calcium sulfate hemihydrate of which was assumed in the prismatic form, and organic salts solution exhibited little effect on the catalystic action to the crystallization, than inorganic salts. In the acidic solution with sulfuric acid(pH=2), needle like crystal of calcium sulfate hemihydrate was obtained. Hydrothermal process with aluminum sulfate solution also showed certain amounts of impurity removal such as phosphorus penataoxide from calcium sulfate hemihydrate.

• Journal of the Korea institute for structural maintenance and inspection
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• v.23 no.7
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• pp.72-79
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• 2019

Concrete is vulnerable to cracks due to volume changes caused by temperature changes, shrinkage during curing, external forces, or poor construction. In particular, concrete placed in electric power tunnel structures can generate cracks by a variety of factors. As a result, these tunnel structures require continuous maintenance. In this study, we investigated the mechanical properties of electric power tunnel concrete using alpha-calcium sulfate hemihydrate, which is an industrial byproduct that has excellent expansion performance. To compensate for the decrease in compressive strength when substituting alpha-calcium sulfate hemihydrate, based on previous research, we added 9% alpha-calcium sulfate hemihydrate and adjusted the amount of admixture while using the same amount of cement. We then evaluated the mechanical properties of the concrete. The results showed that the compressive strength of the concrete was higher than that of ordinary Portland cement (OPC), and the shrinkage of concrete was reduced by more than 30% compared to that of OPC. Therefore, adding 9% of alpha-calcium sulfate hemihydrate is expected to have a significant effect in reducing concrete cracks.

• Journal of the Korean Recycled Construction Resources Institute
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• v.12 no.1
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• pp.25-32
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• 2024

In this study, the mechanical properties of PHC pile concrete using alpha-type hemihydrate gypsum were evaluated. As the replacement ratio of alpha-type hemihydrate gypsum increased, the setting time rapidly accelerated. In particular, when replacement ratio exceeded 20 %, the setting time was shortened due to rapid hydration reaction, making it impossible to secure working time. As the replacement ratio of alpha-type hemihydrate gypsum increased, the ettringite and gypsum peaks tended to increase, and it is believed that the shrinkage of concrete decreased due to the increase in the ettringite peak. At a As the replacement ratio of 5 to 15 % for alpha-type hemihydrate gypsum, the compressive strength increased or was found to be equivalent to that of OPC. But at 20 % substitution, workability deteriorated due to rapid setting, so use of the 5 to 15 % range is considered appropriate.

• Proceedings of the Korea Concrete Institute Conference
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• 2000.10a
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• pp.351-354
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• 2000

In recent years, the world development of alternative construction materials is associated with disposal problems of waste materials as a result of industrial activities. Technologies of refining gypsum to several gypsum modifications ($\alpha$ and $\beta$-hemihydrate) which can be used as construction material in a large scale do actually exist or are under development. This paper provides a technical and economic perspective of the waste gypsum treatment. Especially, several applications particularly of $\alpha$-hemihydrate will be presented, e.g. artificial gypsum aggregate and light-weight masonry units.

• Journal of the Korea Institute of Building Construction
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• v.11 no.2
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• pp.181-188
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• 2011

Spalling must be considered when designing high-strength concrete to cope with fire. This study investigates the temperature rise of steel bar in high-strength concrete coated with fireproof mortar using gypsum exposed to fire. It was found that fireproof mortar using gypsum is more effective in constraining the temperature rise of steel bar in the high strength concrete than fireproof mortar using cement, and that the thinner the cover depth of the fireproof mortar, the more significant the influence of the gypsum. In addition, while there was no difference between ${\alpha}$-hemihydrate mortar and ${\beta}$-hemihydrate mortar on the temperature rise of steel bar, the compressive strength of ${\alpha}$-hemihydrate mortar is higher than that of ${\beta}$-hemihydrate mortar.