• Title, Summary, Keyword: Calcium-Silicate-Hydrate (C-S-H)

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Mechanical Properties of Hydrated Cement Paste: Development of Structure-property Relationships

  • Ghebrab, Tewodros T.;Soroushian, Parviz
    • International Journal of Concrete Structures and Materials
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    • v.4 no.1
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    • pp.37-43
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    • 2010
  • Theoretical models based on modern interpretations of the morphology and interactions of cement hydration products are developed for prediction of the mechanical properties of hydrated cement paste (hcp). The models are based on the emerging nanostructural vision of calcium silicate hydrate (C-S-H) morphology, and account for the intermolecular interactions between nano-scale calcium C-S-H particles. The models also incorporate the effects of capillary porosity and microcracking within hydrated cement paste. The intrinsic modulus of elasticity and tensile strength of hydrated cement paste are determined based on intermolecular interactions between C-S-H nano-particles. Modeling of fracture toughness indicates that frictional pull-out of the micro-scale calcium hydroxide (CH) platelets makes major contributions to the fracture energy of hcp. A tensile strength model was developed for hcp based on the linear elastic fracture mechanics theories. The predicted theoretical models are in reasonable agreements with empirical models developed based on the experimental performance of hcp.

The Reduction of Maximum Hydration Temperature in Cement Paste Using Calcium Silicate Hydrates and Glucose (칼슘실리케이트 수화물과 포도당을 이용한 시멘트 페이스트의 최대 수화온도 저감)

  • Moon, Hoon;Kim, Hyeong-Keun;Ryu, Eun-Ji;Jin, Eun-Ji;Chung, Chul-Woo
    • Journal of the Korea Concrete Institute
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    • v.27 no.3
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    • pp.265-272
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    • 2015
  • In this study, a method to reduce temperature rise due to hydration in mass concrete is investigated. It is to use retarder (glucose) for reducing heat of hydration and to use calcium silicate hydrate (C-S-H) for compensating the retardation effect due to its role as a nucleation seed. For this purpose, the temperature rise of cement paste due to hydration was measured and the effect of using both C-S-H and glucose on setting and 28-day compressive strength of mortar specimens was investigated. According to the experimental results, using C-S-H and glucose caused the reduction in the maximum temperature but accelerated the time to reach the maximum temperature compared to that of retarded cement paste using glucose. In addition, using C-S-H and glucose did not show significant effect on 28-day compressive strength of mortar specimens, indicating that the method shown in this study can be a successful alternative to control maximum temperature rise in mass concrete.

Hydration of Modified Converter Slag (개질한 전노슬래그의 수화반응)

  • 엄태선;최상흘
    • Journal of the Korean Ceramic Society
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    • v.18 no.3
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    • pp.157-162
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    • 1981
  • A converter slag has been heat-treated above melting point at reduced condition by cokes. As the result, most iron was separated. To make hydraulic compounds, calcium oxide was added to the reduced converter slag and the mixtures were sintered. This modified converter slag clinker mainly contained tricalcium silicate and calcium aluminates, and have a great potential to be a good hydraulic cement. The hydrates of the hydraulic compounds and gypsum with and without granulated slags, were mainly C-S-H, ettringite, calcium monosulfoaluminate hydrate, calcium aluminate hydrate, and $Ca(OH)_2$

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Nanostructural Deformation Analysis of Tricalcium Silicate Paste by Atomic Pair Distribution Function (원자짝 분포 함수를 이용한 칼슘 실리케이트 경화체의 나노 구조 변형 거동 해석)

  • Bae, Sung-Chul;Chang, Yoo-Hyun;Jee, Hyeon-Seok
    • Proceedings of the Korean Institute of Building Construction Conference
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    • pp.94-95
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    • 2016
  • Calcium Silicate Hydrate (C-S-H), which takes up most of the hydration products of Portland Cement (PC), has the greatest impact on the mechanical behavior and strength development of concrete. The exact mechanism of its deformation, however, has not yet been elucidated. The present study aims to demonstrate the mechanism of nano-deformation behavior of C-S-H in tricalcium silicate paste under compressive loading, unloading and reloading by interpreting atomic pair distribution function (PDF) based on synchrotron X-ray scattering. The strain of the tricalcium silicate paste for a short-range of 0 ~ 20 Å under compressive load exhibited two stages, I) nano-packing of interlayer of C-S-H and II) micro-packing of C-S-H globules, whereas the deformation for a long-range order of 20 ~ 40 Å was similar to that of a calcium hydroxide phase measured by Bragg peak shift. Moreover, the residual strains due to the plastic deformation of C-S-H was clearly observed.

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Reaction of the System of Coal Fly Ash-Sulfuric Acid-Calcium Hydroxide (플라이 애쉬-황산-수한화칼슘계의 반응)

  • 송종택;안민선;정문영
    • Journal of the Korean Ceramic Society
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    • v.33 no.12
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    • pp.1331-1338
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    • 1996
  • In order to investigate the reaction in the system of fly ash-sulfuric acid-calcium hydroxide the hydrates were produced by the addition of Ca(OH)2 to fly ash activated with sulfuric acid at various temperatures. And then they were characterized by XRD. SEM and TG-DTA. It was found that in the reaction of fly ash with sulfuric acid fly ash was not decomposed but Al2O3 and SiO2 component in it were activated. The addition of calcium hydroxide into this system resulted in the formation of ettringite and calcium silicate hydrate (C-S-H) As the concentration of sulfuric acid and reaction temperature increased the amount of calcium hydroxide decreased fast. At this time gypsum produced by the reaction calcium hydroxide with sulfuric acid was consumed to form ettringite. Accordingly the formation of ettringite increased with calcium hydroxide and reaction time. And it showed faster than the formation of C-S-H.

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FIXATION OF LEAD CONTAMINANTS IN Pb-DOPED SOLIDIFIED WASTE FORMS

  • Lee, Dong-Jin;Chung, David;Hwang, Jong-Yeon;Choi, Hyun-Jin
    • Environmental Engineering Research
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    • v.12 no.3
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    • pp.101-108
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    • 2007
  • Fixation of lead contaminants in the solidification/stabilization using Portland cement has been investigated by X-ray diffraction, scanning electron microscopy and compressive strength. The presence of lead was observed to produce lead carbonate sulfate hydroxide ($Pb_4SO_4(CO_3)_2(OH)_2$), lead carbonate hydroxide hydrate ($3PbCO_3{\cdot}2Pb(OH)_2{\cdot}H_2O$) and two other unidentified lead salts in cavity areas and was observed to significantly retard the hydration of cement. By 28 days, howevere, the XRD peaks of most of the lead precipitates have essentially disappeared with only residual traces of lead carbonate sulfate hydroxide and lead carbonate hydroxide hydrate evident. After 28 days of curing, hydration appears well advanced with a strong portlandite peak present though C-S-H gel peaks are not particularly evident. Lead species produced with the dissolution of lead precipitates are fixed into the cement matrix to be calcium lead silicate hydrate (C-Pb-S-H) during cement-based solidification.

Diffusion study for chloride ions and water molecules in C-S-H gel in nano-scale using molecular dynamics: Case study of tobermorite

  • Zehtab, Behnam;Tarighat, Amir
    • Advances in concrete construction
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    • v.4 no.4
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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.

Investigation of Cement Matrix Compositions of Nanosilica Blended Concrete

  • Kim, Jung Joong;Moon, Jiho;Youm, Kwang-Soo;Lee, Hak-Eun;Lim, Nam-Hyoung
    • International Journal of Railway
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    • v.7 no.3
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    • pp.85-89
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    • 2014
  • The use of pozzolanic materials in concrete mixtures can enhance the mechanical properties and durability of concrete. By reactions with pozzolanic materials and calcium hydroxide in cement matrix, calcium-silicate-hydrate (C-S-H) increases and calcium hydroxide decreases in cement matrix of concrete. Consequently, the volume of solid materials increases. The pozzolanic particles also fill spaces between clinker grains, thereby resulting in a denser cement matrix and interfacial transition zone between cement matrix and aggregates; this lowers the permeability and increases the compressive strength of concrete. Moreover, the total contents of alkali in concrete are reduced by replacing cements with pozzolanic materials; this prevents cracks due to alkali-aggregate reaction (AAR). In this study, nanosilica is incorporated in cement pastes. The differences of microstructural compositions between the hydrated cements with and without nanosilica are examined using nanoindentation, XRDA and $^{29}Si$ MAS NMR. The results can be used for a basic research to enhance durability of concrete slab tracks and concrete railway sleepers.

THE MICROSTRUCTURE OF Pb-DOPED SOLIDIFIED WASTE FORMS USING PORTLAND CEMENT AND CALCITE

  • Yoo, Hee-Chan;Lee, Dong-Jin
    • Environmental Engineering Research
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    • v.11 no.1
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    • pp.54-61
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    • 2006
  • An electron probe microanalysis (EPMA) investigation can provide quantitative and qualitative insight into the nature of the surface and bulk chemistry on solidified waste forms(SWF). The proportion of Pb in grain areas is below 0.3 wt. %, and the proportion near the border of the grain slightly increases to 0.98 wt. % but in the inter-particle areas farther from the grain, the concentration of Pb markedly increases. It is apparent that very little Pb diffuses into the tricalcium silicate($C_3S$) particles and most of the Pb exists as precipitates of sulfate, hydroxide, and carbonate in the cavity areas between $C_3S$ grains. Calcite additions on Pb-doped SWF are also observed to induce deeper incorporation of lead into the cement grains with EPMA line-analysis of cross-sections of cement grains. The line-analysis reveals the presence of $0.2{\sim}5$ weight % Pb over $5\;{\mu}m$ from cement grain boundaries. In the inter-particle areas, the ratio of Ca, Si, Al and S to Pb is relatively similar even at some distance from the grain border and the Pb (wt. %) ratio is reasonably constant throughout the whole inter-particles area. It is apparent that the enhanced development of C-S-H on addition of calcite can increasingly absorbs lead species within the silica matrix.

Development of Fly Ash/slag Cement Using Alkali-activated Reaction(2) - Reaction products and microstructure - (알칼리 활성반응을 이용한 플라이 애쉬/슬래그 시멘트 개발(2) - 반응생성물과 미세구조 -)

  • Park, Sang-Sook;Kang, Hwa-Young;Han, Kwan-Su
    • Journal of Korean Society of Environmental Engineers
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    • v.29 no.7
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    • pp.810-819
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    • 2007
  • Investigation of alkali activation of fly ash and blast furnace slag was carried out using waterglass and sodium hydroxide. XRD, FTIR, $^{29}Si$ and $^{27}Al$ NMR, TGA and SEM were used to observed the reaction products and microstructure of the fly ash/slag cement (FSC) pastes. The reaction products were amorphous or low-ordered calcium silicate hydrate and aluminosilicate gel produced from alkali activation of blast furnace slag and fly ash, respectively. On the basis of this investigation, waterglass solution with a modulus(Ms) of 1.0 and 1.2 is recommended for alkali activation of fly ash and blast furnace slag. Morphology of FSC pastes alkali-activated with Ms of 1.0 and 1.2 shows a more solid and continuous matrix due to restructuring of gel-like reaction products from alkali-activated fly ash and blast furnace slag together with another hydrolysis product(i.e., silica gel) from water glass.