• 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.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.11a
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• pp.214-217
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• 2004

숭화법을 이용한 탄화규소(Silicon carbide) 단결정 성장시 사용되는 원료의 상(phase)이 단결정 성장에 미치는 영향을 알아보기 위해 알파형 탄화규소 분말(${\alpha}-SiC$ powder)과 베타형 탄화규소 분말(${\beta}-SiC$ powder)을 각각 사용하였다. 알파형 탄화규소 분말을 사용한 경우에 단결정(single-crystal)을 성장할 수 있었으나, 베타형 탄화규소 분말을 사용하였을 때에는 다결정(poly-crystal)이 성장되었다. 다결정 형성요인에 관한 EPMA 분석결과, 베타형 탄화규소 분말의 탄소에 대한 실리콘의 원소조성비$(N_{Si}/N_C\;=\;1.57)$가 알파형 탄화규소 분말의 경우보다$(N_{Si}/N_C\;=\;0.81)$ 높음을 확인하였다. 따라서 흑연도가니(crucible) 내부의 실리콘 원자가 알파형 탄화규소 분말을 사용하는 경우보다 높은 과포화상태가 되어 종자정 표면에 미세한 실리콘 액적(droplet)이 중착되고 이것으로부터 일정하지 않은 방향성(random orientation)을 갖는 탄화규소 다결정(다양한 방향성을 갖는 다형 포함)이 성장한 것으로 실리콘과 탄소 원소에 대한 EPMA 지도(map) 결과를 통해 확인할 수 있었다.

• 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.

• 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.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2022.04a
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• pp.152-153
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• 2022

In this study, the mechanical properties of PHC Pile were investigated using α-calcium sulfate hemihydrate, an industrial by-product with excellent expansion performance. As a result, the compressive strength of PHC pile showed a tendency to be higher than that of general Portland cement (OPC).

• Journal of Korea Ship Safrty Technology Authority
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• s.38
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• pp.2-11
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• 2015

최근 저탄소 녹색성장 및 그린에너지 개발 정책에 힘입어 외연기관의 일종으로 Stirling Engine에 대한 관심이 고조되고 있다. 스털링엔진은 크게 알파, 베타, 감마형의 3가지 방식으로 구분되어지며 그 중 감마타입 엔진의 설계가 용이하고 다양한 적용이 가능하다는 특징이 있음에도 실린더와 크랭크간의 접속거리 문제로 인하여 알파, 베타 타입에 비하여 용적을 크게 차지하는 문제가 있었다. 이를 해결하기 위한 방안으로 주로 알파형에 적용하는 Yoke crank를 적용하면 용적을 줄임과 동시에 실린더의 병렬화에도 유리하다. 금번 연구에서는 기존의 Ross Yoke crank 설계기법에서 나아가 감마형 스털링엔진의 Yoke crank 설계를 더욱 단순하고 효율적으로 적용할 수 있는 방법을 제시한다.

• Magazine of RCR
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• v.4 no.4
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• pp.50-53
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• 2009

• Applied Chemistry for Engineering
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• v.17 no.6
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• pp.619-624
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• 2006

This study was performed to investigate the formation process of calcium sulfate ${\alpha}$-hemihydrate from FGD gypsum produced at thermal power plant burning bituminous coal. The experimental results showed that calcium sulfate $\alpha$-hemihydrate with a large aspect ratio was produced in the temperature range of $120^{\circ}C$ and $140^{\circ}C$ in the absence of additives through dissolution-recrystallization mechanism. It was also observed that addition of Na-succinate as a catalyst changed crystal shape from acicular to prismatic, resulting in decreased water/powder ratio down to 33%. Optimum concentration of Na-succinate was 20mM. It was confirmed that the optimum moulding pressure and moisture content of moulded body from FGD gypsum were $30kg_f/cm^2$ and between 10% and 15% respectively, which prevent moulded body from collapsing and maximize the capillary effect by given pore volume while autoclaving.

• Journal of the Korea institute for structural maintenance and inspection
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• v.26 no.1
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• pp.67-72
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• 2022

Concrete prevents corrosion of reinforcing bars due to its strong alkalinity. However, in the sea, strong alkali components with a pH of 12 to 13 are eluted, which adversely affects the ecological environment and growth of marine organisms. In this study, the mechanical properties and durability of the low alkali mortar were evaluated for the development of a low alkali mortar for the 3D printed artificial reefs. As a result of evaluation of strength characteristics, the α-35 mixture, which were produced with fly ash, silica fume and α-hemihydrate gypsum, satisfied the strength requirement 27 MPa in terms of compressive strength. As a result of pH measurement, it was found that mixing with alpha-type hemihydrate gypsum resulted in minimizing pH due to the the formation of calcium sulfate instead of calcium hydroxide production. As a result of the chloride ion penetration resistance test, the α-35 mixture exhibited the best performance, 3844C. As a result of measuring the length change over time, the α-35 mixture showed the shrinkage 33.5% less compared to the Plain mix.