• Journal of the Korea Concrete Institute
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• v.21 no.6
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• pp.729-735
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• 2009

In this study, it is experimentally verified a feasibility of the wasted phosphogypsum ($CaSO_4/H_2O$) that is a byproduct from the phosphoric acid process of manufacturing fertilizers can be applied as an admixture in slag cement. For the test, phosphogypsum is modified as dihydrate, hemihydrate, type III anhydrite, and type II anhydrite, and then chemical characteristics and mechanical properties of various slag cements containing above mentioned gypsum materials were analyzed. The test results show that the gypsum made at high temperature has better quality with decrease of water-soluble phosphoric acid ($S-P_2O_5$) which has an effect on the quality of cement. And type II anhydrite shows superior quality in terms of drying shrinkage and the compressive strength of cement paste with hemihydrate at 56 days is higher than other gypsum material.

• Cement
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• s.61
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• pp.53-57
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• 1975

1) 본논문은 Zement-Kalk-Gips 75년도 8월호에 게재된 V. Satava씨 및 J. Komrska씨의 $\ulcorner$Gips und $\SiO_2$-Hydrosolein neues Bindemittel$\lrcorner$을 번역 발췌한 것으로 주요 내용은 다음과 같다. 2) $\SiO_2$ Hydrosol 중의 반수석고경화 현탁액의 강도보다 높다. 3) Hydrosol중의 $\SiO_2$ 입자는 행동이 액상과 같으므로 반수석고 현탁액의 점도는 Hydrosol중이나 물중이나 유사하며 단지 $\SiO_2$의 부피만큼 물, 석고비를 감소시킨다. 4) 경화과정에서 단위 부피당 석고 결정이 차지하는 부피가 크므로 순수하게 물을 사용했을 때보다는 강도가 높다. 5) $\SiO_2$ 분자는 경화물질의 Skeleton속의 기공을 채워 표면의 특성에 영향을 준다.

• Applied Chemistry for Engineering
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• v.8 no.5
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• pp.822-829
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• 1997

When $Al_2(SO_4)_3$ as an accelerator was added to $\beta$-hemihydrate gypsum, the setting time, mobility and compressive strength properties of $\beta$-hemihydrate gypsum were examined with the adding of two types grounded gypsum crushed by ball mill. By 15wt% adding of 7% $Al_2(SO_4)_3$ dilute solution, the setting time of $\beta$-hemihydrate gypsum was sharply accelerated than that of non-added $\beta$-hemihydrate gypsum. When ground phospho gypsum(PG) and chemical gypsum(CG) were added to $\beta$-hemihydrate gypsum, the initial and final setting time of $\beta$-hemihydrate gypsum were accelerated markedly with the increasing of grinding time and added amount of ground phospho gypsum. Especially, this trend largely presented when ground phospho gypsum was added to $\beta$-hemihydrate gypsum. The compressive strength of $\beta$-hemihydrate gypsum added by ground phospho and chemical gypsum was largely increased at initial curing time such as 1, 3 days. Particularly, the compressive strength of $\beta$-hemihydrate gypsum added by ground phospho gypsum was increased by 15~20% than that of ground chemical gypsum.

• 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.

• Journal of the Mineralogical Society of Korea
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• v.21 no.2
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• pp.193-200
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• 2008

We tried to evaporate and dry the moisture contained Flue gas desulfurization gypsum and phosphogypsum by using the microwave directly. In the result of the heating to the Flue gas desulfurization gypsum and phosphogypsum using 2.45 GHz microwave which was created by magnetron 700 W, 1,000 W and 1,700 W, respectively. According to the increasing the microwave output intensity from 700 W to 1,700 W, the evaporate time of moisture was shortened from 10 to 3 minutes. Gypsum were changed to calcium sulfate hemihydrate. However, ${\beta}$-calcium sulfate hemi-hydrate were not changed to anhydrite.

• Journal of the Korea Institute of Building Construction
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• v.16 no.1
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• pp.59-65
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• 2016

This study examined the compressive strength development and pH values of alpha-calcium sulfate hemihydrate(${\alpha}-CH$)-based binders developed for vegetation concrete with neutral pH between 6~7. Considering cost down and strength enhancement of the prepared binders, the ${\alpha}-CH$ was partially replaced by ground granulated blast furnace slag(GGBS), fly ash(FA), or ordinary Portland cement(OPC) by 25% and 50%. The compressive strength of mortars using 100% ${\alpha}-CH$ was 50% lower than that of 100% OPC mortars. With the increase of the replacement level of GGBS or FA, the compressive strength of ${\alpha}-CH$-based mortars tended to decrease, whereas the pH values were maintained to be 6.5~7.5. The main hydration products of ${\alpha}-CH$-based binders with GGBS or FA were a gypsum($CaSO_4$), whereas portlandite($Ca(OH)_2$) was not observed in such binders. Meanwhile, the pH values of ${\alpha}-CH$-based binders with OPC exceeded 11.5 due to the formation of $Ca(OH)_2$ phase as a hydration product. From the thermogravimetric analysis, the amount of $Ca(OH)_2$ in ${\alpha}-CH$-based binders with OPC was evaluated to be approximately 10% of the cement content.

• 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.

• Cement
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• s.61
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• pp.58-63
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• 1975

1) 본연구논문은 Zement-Kalk-Gips 1975년도 8월호에 게재된 TH Chavatal씨의 $\ulcorner$Systematische Versucke zur Hydrophbierung des Gipses$\lrcorner$를 번역 발췌한 것으로 요약하면 다음과 같다. 2) 현재 사용가능한 agent 중에서 가장 효과적인 것을 선택하여 석고에 장기 배수성을 가지게 하는 것이 가능한가의 여부에 대한 실험 결과이다. 3) 원필자의 실험은 28일간 계속되었으며 $\alpha$형 및 $\beta$형 반수석고에 대해 물의 흡수, 강도변화, 체적의 감소 및 표면의 손상 등에 대해 계통적으로 실험하였다. 4) $\alpha$형 및 $\beta$형 반수석고에 대해 어떤 agent도 안전히 배수성을 가지게 할 수는 없었으며 이 두 석고의 물에 대한 저항은 거의 대동소이하였다.

• 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.38 no.5
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• pp.446-453
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• 2001

본 논문에서는 석고형태에 따른 belite-rich cement(BRC)의 수화성상 및 혼화제의 흡착거동으로부터 시멘트의 유동성에 미치는 영향성을 조사하였다. 또한, 보통 포틀랜드 시멘트(OPC)의 경우와도 그 영향성을 비교 검토하였다. 유동특성을 측정한 결과, 폴리카르복실산계 혼화제 사용시 반수와 이수석고를 첨가한 BRC가 미니슬럼프 값이 약 $\pm$20cm 근방의 수치를 보였으며, 무수석고를 첨가한 것과 OPC에서는 낮은 슬럼프치를 보였다. 초기 수화의 경우, XRD와 DSC에서 Ca(OH)$_2$의 생성량의 정도가 BRC 2-C(반수)>BRC 1-C(이수)>BRC 3-C(무수)의 순서로 줄어들기 때문에 장기강도측면에서도 반수석고와 이수석고를 동시에 사용하는 것이 우수할 것으로 추정된다. 또한 이 결과는 비표면적의 데이터와도 일치함을 보였다.