• Title/Summary/Keyword: C-S-H

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Influence on mechanical property of C-S-H(I) due to its structural modification (C-S-H(I)의 분자구조변형을 통한 기계적 거동의 변화)

  • Oh, Jae-Eun;Monteiro, Paulo J.M.
    • Proceedings of the Korea Concrete Institute Conference
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    • pp.473-474
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    • 2010
  • This high pressure synchrotron X-ray diffraction study examined the change of bulk modulus of C-S-H(I), core material creating strength in alkali-activated slag cement as well as structural model of C-S-H, mainly attributed to Al-substitution for Si, which occurs at the bridging tetrahedral sites in dreierketten silicate chains in the nanostructure of C-S-H(I). This study presents that Al-substitution in C-S-H(I) does not affect the bulk modulus of C-S-H(I), which is surprising because many researchers have expected that Al-substitution should induce some critical change in mechanical properties of C-S-H(I).

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Interaction Experiment on Chloride Ion Adsorption Behavior of C-S-H Phases (C-S-H 상의 염소이온 흡착 메커니즘 규명을 위한 반응 작용 실험)

  • Yoon, In-Seok
    • Journal of the Korea Concrete Institute
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    • v.29 no.1
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    • pp.65-75
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    • 2017
  • C-S-H phase is the most abundant reaction product, occupying about 50~60% of cement paste volume. The phase is also responsible for most of engineering properties of cement paste. This is not because it is intrinsically strong or stable, but because it forms a continuous layer that binds together the original cement particles into a cohesive whole. The binding ability of C-S-H phase arises from its nanometer-level structure. In terms of chloride penetration in concrete, C-S-H phase is known to adsorb chloride ions, however, its mechanism is very complicated and still not clear. The purpose of this study is to examine the interaction between chloride ions and C-S-H phase with various Ca/Si ratios and identify the adsorption mechanism. C-S-H phase can absorb chloride ions with 3 steps. In the C-S-H phase with low Ca/Si ratios, momentary physical adsorption could not be expected. Physical adsorption is strongly dependent on electro-kinetic interaction between surface area of C-S-H phase and chloride ions. For C-S-H phase with high Ca/Si ratio, electrical kinetic interaction was strongly activated and the amount of surface complexation increased. However, chemical adsorption could not be activated for C-S-H phase with high Ca/Si ratio. The reason can be explained in such a speculation that chloride ions cannot be penetrated and adsorbed chemically. Thus, the maximum chloride adsorption capacity was obtained from the C-S-H phase with a 1.50 Ca/Si ratio.

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.

Effects of Ca/Si Molar Ratio on the Interatomic Distance of Synthetic Calcium Silicate Hydrate (C-S-H) at Elevated Temperature (고온 가열시 Ca/Si 몰비율에 따른 합성 칼슘 실리케이트 수화물(C-S-H)의 구성 원자간 거리 변화)

  • Im, Su-Min;Bae, Sung Chul
    • Proceedings of the Korean Institute of Building Construction Conference
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    • pp.144-145
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    • 2021
  • Calcium silicate hydrate(C-S-H) is the principal binding phase that controls the strength and thermal stability of concrete. However, the effects of high temperature on the lattice structure and interatomic structure of C-S-H remains poorly understood due to its nanocrystallinity. This study aims to elucidate the change in interatomic distance of synthetic C-S-H with different Ca/Si molar ratios after exposure to high temperature via high energy X-ray scattering experiment which is a powerful analytical tool for amorphous materials.

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Creep Mechanisms of Calcium-Silicate-Hydrate: An Overview of Recent Advances and Challenges

  • Ye, Hailong
    • International Journal of Concrete Structures and Materials
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    • v.9 no.4
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    • pp.453-462
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    • 2015
  • A critical review on existing creep theories in calcium-silicate-hydrate (C-S-H) is presented with an emphasis on several fundamental questions (e.g. the roles of water, relative humidity, temperature, atomic ordering of C-S-H). A consensus on the rearrangement of nanostructures of C-S-H as a main consequence of creep, has almost been achieved. However, main disagreement still exists on two basic aspects regarding creep mechanisms: (1) at which site the creep occurs, like at interlayer, intergranular, or regions where C-S-H has a relatively higher solubility; (2) how the structural rearrangement evolutes, like in a manner of interlayer sliding, intra-transfer of water at various scales, recrystallization of gelled-like particles, or dissolution-diffusion-reprecipitation at inter-particle boundary. The further understanding of creep behavior of C-S-H relies heavily on the appropriate characterization of its nanostructure.

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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Fly ash-Slag-Cement Composite

  • Bang, Wan-Keun;Lee, Seung-Kyou;Lee, Seung-Heun;Kim, Chang-Eun
    • The Korean Journal of Ceramics
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    • v.6 no.3
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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.

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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.

Properties of Hydration and Strength of Sol-gol Derived Fine Particle in the System $CaO-P_2O_5-SiO_2$ (졸겔법에 의한 $CaO-P_2O_5-SiO_2$계 미세분말의 수화 및 강도특성)

  • 이형우;김정환
    • Journal of the Korean Ceramic Society
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    • v.31 no.10
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    • pp.1231-1239
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    • 1994
  • In this study, gel powder which had relatively high hydration reactivity in CaO and P2O5 rich composition of CaO-P2O5-SiO2-H2O system was prepared by sol-gel process and its hydrated specimen was manufactured. The it was investigated to appropriate calcination temperature in sol-gel process which hydrated specimen of gel powder have proven to strength and the effect of factors influenced strength in hydration process. The major product of before and after hydration reaction was hydroxyapatite, and crystalline phase of C-S-H was already formed during gelation process. After hydration reaction of pressed specimen, crystalline phase of C-S-P-H was formed. It was hydrated product of silicocarnotite (5CaO.P2O5.SiO2). Gel phases of C-S-H and C-S-P-H occured as a result of partial substitution of amorphous silica by P2O5 was formed. The strength of hydrated hardened body is developed by strong bonding and bridging between the gel phases of C-S-H or C-S-P-H and the crystalline products such as hydroxyapatite, Ca(OH)2 C-S-H and C-S-P-H. In addition, the ultrafine gel powder have an great effect on increase of hydration reaction.

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