• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2006년도 춘계학술대회
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• pp.387-390
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• 2006

We report here that under strong attacksof external $CH_4$ guest molecules the sII and sH methane hydrates are structurally transformed to the crystalline me framework of sI, leading to favorable change of the lattice dimension of the host-guest networks. The High Power Decoupling $^{13}C$ NMR and Raman spectroscopies were used to identify structure transitions of the mixed $CH_4+C_2H_6$ hydrates (sIIl) and hydrocarbons (methylcyclohexane, isopentane) + $CH_4$ hydrates (sH). The resulting spectra indicate that most of the synthesized sII and sH hydrates were transformed to methane hydrate of sl under 110 bar and particularly the coexistence of sl with sII or sH appear according to the surrounding methane-rich gas conditions. The present findings might be expected to Provide rational evidences regarding the preponderant occurrence of naturally-occurring sI methane hydrates in marine sediments.

• Computers and Concrete
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• 제13권6호
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• pp.695-707
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• 2014

This study investigated the chloride binding isotherms of various cement types, especially the contributions of C-S-H and AFm hydrates to the chloride binding isotherms were determined. Ordinary Portland cement (OPC), Modified cement (MC), Rapid-hardening Portland cement (RHC) and Low-heat Portland cement (LHC) were used. The total chloride contents and free chloride contents were analyzed by ASTM. The contents of C-S-H, AFm hydrates and Friedel's salt were determined by X-ray diffraction Rietveld (XRD Rietveld) analysis. The results showed that OPC had the highest chloride binding capacity, and, LHC had the lowest binding capacity of chloride ions. MC and RHC had very similar capacities to bind chloride ions. Experimental equations which distinguish the chemically bound chloride and physically bound chloride were formulated to determine amounts of the bound chloride basing on chloride binding capacity of hydrates.

• The Korean Journal of Ceramics
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• 제6권3호
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• pp.286-290
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• 2000

The hydration behavior of fly ash and slag on cement paste were investigated. Early stage of hydration reaction was delayed by mixing fly ash and/or slag with cement, but production of C-S-H hydrates by pozzolanic reaction densified the microstructure. The Ca/Si ratio of C-S-H hydrates in OPC and blended cement of fly ash 50%, slag 50%, fly ash+slag 50% were 2.24, 1.80, 1.82 and 1.97, respectively. The C-S-H gel with low Ca/Si ratio showed rather reticulate than needle-like structure.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2020년도 가을 학술논문 발표대회
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• pp.151-152
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• 2020

When concrete is exposed to fire, the thermal decomposition of hydrates of Portland cement paste results in critical damage to the concrete structure of a building. Recently, nanosilica arose as the effective nano-additive which can enhance the thermal resistance of the cementitious materials. However, the mechanism of the enhancement was not elucidated specifically. In this study, we investigated the properties of calcium silicate hydrates(C-S-H)of the nanosilica incorporated cement paste after heating to different heating temperatures (200℃, 500℃, and 800℃) by 29Si nuclear magnetic resonance. The results showed that the polymerization of C-S-H of nanosilica incorporated samples was larger than ordinary cement paste after heating to 200℃, and C-S-H formed during heating process to 500℃ due to the pozzolanic reaction during heating process.

• 한국세라믹학회지
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• 제23권3호
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• pp.27-34
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• 1986

The hydration of flyash-$Ca(OH)_2-CaSO_4$.$2H_2O$ system was stuedied with varing mixing ratio of flyahs $Ca(OH)_2$ and caSO4.2H2O The samples were steam-cured for 1-7 days at 9$0^{\circ}C$. The optimum mixing composition was flyash : Ca (OH)2=65:35 with 15% $CaSO_4$.42H_2O$ added which produced the hardened material having the best compressive strength (300kg/$cm^2$) Also the low specific gravity(1, 2) of the hardened paste suggests the possibility that it can be used as a light-weight building material. The added $CaSO_4$.42H_2O$ constituted calcium-sulfo-aluminate hydrates which activates the formation of C-S-H hy-drates. Both hydrates developed the strength of hardened paste. The amount of calcium-sulfo-aluminate hydrates was increased when the $CaSO_4$.42H_2O$ was added over 15% however the increased amount did not help the development of strength because of the individually grown calcium-sulfo-aluminate hydrates.

• Advances in concrete construction
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• 제4권4호
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• pp.305-317
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• 2016

Porous materials such as concrete could be subjected to aggressive ions transport. Durability of cement paste is extremely depended on water and ions penetration into its interior sections. These ions transport could lead different damages depending on reactivity of ions, their concentrations and diffusion coefficients. In this paper, chloride diffusion process in cement hydrates is simulated at atomistic scale using molecular dynamics. Most important phase of cement hydrates is calcium silicate hydrate (C-S-H). Tobermorite, one of the most famous crystal analogues of C-S-H, is used as substrate in the simulation model. To conduct simulation, a nanopore is considered in the middle of simulation cell to place water molecules and aggressive ions. Different chloride salts are considered in models to find out which one is better for calculation of the transport properties. Diffusion coefficients of water molecules and chloride ions are calculated and validated with existing analytical and experimental works. There are relatively good agreements among simulation outputs and experimental results.

• 한국세라믹학회지
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• 제34권5호
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• pp.491-499
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• 1997

High flexible lightweight composites containing tobermorite as a main mineral is produced using various amorphous silicates, lime, cement and fibers. Here, Mechanical properties of the composites were studied by observing microstructures of hydrates and fibers. Amorphous silicates having better hydraulicity retarded the crystallization of tobermorite due to better formation of C-S-H gel in water bath curing, but, difficult conversion from C-S-H gel to tobermorite in hydrothermal reaction. In the low molar ratio of CaO/SiO2 (0.67), faster crystalization was observed dued to more impurities such as Al2O3 alkali, resulting in improving mechanical properties due to small crystal size and many contact points. It was identified that a lot of calcium silicate hydates formed at surface of pulps increase bonding strength and the crack-resistance of matrix in the composites, but decrease hardness and compressive strength. The choice of amorpous silicates having better hydraulicity, low CaO/SiO2 adding each fibers bellow about 5% in the raw mixs and lower molding pressure should be needed at improve mechanical properties of composites.

• 콘크리트학회논문집
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• 제27권1호
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• pp.85-92
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• 2015

콘크리트 내 염소이온은 콘크리트 내부로 침투하여 철근부식을 일으키는 주요 요인이다. 그런데 내재된 염소이온의 일부는 시멘트의 수화물과 반응하여 물리 또는 화학적 흡착을 유발하여 침투속도는 느려진다. 이때 시멘트의 수화물이 염소이온의 고정화에 영향을 미치는 요인이므로, 본 논문은 독립적인 시멘트 수화물에서 염소의 흡착에 대하여 초점을 두어 연구하였다. 본 연구의 목적은 시멘트 수화물이 염소이온을 흡착하는 시간의존적 거동을 고찰하여 염소이온 고정화의 메커니즘을 구명하는 것이다. 시멘트 수화물 중 AFt 상과 CH 상은 염소이온을 흡착하지 못하였으나 C-S-H 상과 AFm 상은 염소 흡착능력을 갖고 있는 것으로 나타났다. 특히, AFm 상은 40일 동안 느린 속도로 화학적 흡착 거동을 보인 반면, C-S-H 상은 순간적 물리흡착, 물리화학적 흡착, 그리고 화학적 흡착의 3단계로 구분되어 순차적인 흡착거동을 보였다. 반응 실험결과를 토대로, C-S-H 상과 AFm 상의 흡착 거동 해석기법이 제안되었다. 본 연구는 염소이온의 도입원에 따른 흡착 메커니즘을 이해를 토대로, 염소이온의 도입원에 따른 염소이온의 침투속도를 산정하는데 활용될 수 있을 것으로 기대된다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2005년도 추계 학술발표회 제17권2호
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• pp.583-586
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• 2005

Strength of concrete is very important factor in design and quality management and may represent overall quality of concrete. Such strength of concrete may differ depending on amount of cement mixed, water and fine aggregate ratio. Classic concrete products have been produced mainly with ordinary portland cement(hereinafter 'cement'), water and fine aggregate as shown above, but various additives and mixture materials have been used for concrete manufacturing, along with development of high functional concrete and diversification of structures. Various kinds of chemical mixtures agents and mixture materials have been used as it requires concretes with other features which cannot be solved with existing materials only, such as high strength, high flexibility and no-separation in the water. Such addition of various mixture agents may cause change in cement hydrate, affecting strength. Hydration of cement is the process of producing potassium hydroxide, C-S-H, C-A-H and Ettringite, while causing heat generation reaction after it is mixed with water, and generation amounts of such hydrates play lots of roles in condensation and hardening. This study aims to analyze its strength and features with hydrates by making specimen according to curing temperature, types of mixture agent, mixing ratio and ages and by analyzing such hydrates in order to analyze role of cement hydrate on early strength of concrete.

• 한국세라믹학회지
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• 제22권2호
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• pp.33-38
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• 1985

The hydration of supersulphated slag cement which is the mixture of granuloated blast furnace slag anhydrite $C_4A_3$ type clinker and calcined dolomite was studied by X-ray diffraction differential thermal analysis scanning electron microscope observation and measurement of the rate of heat liberation. The main hydrates were ettrigite and C-S-H. This supersulphated slag cement enhanced rapid-hardening and increased in strength at early stage due to the much of ettrigite. Furthermore the hardened cement became stronger due to the C-S-H that was produced from the hydration of the $eta$-$C_2S$ in $C_4A_3$ type clinker and the hydration of the dissolved components from slag at later period.