Structure alteration of C-S-H (calcium silicate hydrated phases) caused by sorption of caesium

Iwaida, Takeshi; Nagasaki, Shinya; Tanaka, Satoru; Yaita, Tsuyoshi; Tachimori, Shoichi

doi:10.1524/ract.2002.90.9-11_2002.677

Cited by 19 publications

(10 citation statements)

References 7 publications

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“…This contradicts the observations reported in Ref. [9]. These experimental results may be caused by drying the samples before characterization.…”

Section: Discussioncontrasting

confidence: 95%

“…After MD relaxation, the bulk and shear moduli are calculated at 0 K. Volume expansion is measured at 300 K. Figure 4(a) shows significant volume expansion that increases linearly with Cs uptake. This is consistent with changes in the basal distances measured by x-ray diffraction after exposure of C-S-H to CsCl and CsOH [9]. In Fig.…”

Section: Effect On Mechanical Propertiessupporting

confidence: 89%

“…Moreover, the Ca/Si ratios used in Ref. [9] are lower than 1.0, while the models presented here have Ca/Si ratios greater than 1.0. Finally, it is possible that our model failed to capture this phenomenon because of the limitations of CSH-FF.…”

Section: Discussionmentioning

confidence: 64%

“…We note that the effect of the Ca/Si ratio of the C-S-H on the Cs retention is the subject of debate in the literature-most studies found that Cs retention decreases with an increase of the Ca/Si ratio [7,11,14,15], but one study found the opposite [16]. Iwaida et al [9] suggest that Cs fragments the tobemorite-type layer. Tobermorite is a C-S-H mineral, with a Ca/Si ratio of 0.83, which is composed of oxide planes separated by hydrated interlayers, thought to resemble the oxide layers of C-S-H in cement paste.…”

Section: Introductionmentioning

confidence: 94%

“…We refer the reader to a review by Evans [7] about the binding mechanisms * laurent.beland@queensu.ca of radionuclides to cement. There is a consensus that C-S-H is the main phase responsible for Cs binding [8][9][10][11] and that the main sorption process of Cs in CSH is ion exchange [11][12][13]. We note that the effect of the Ca/Si ratio of the C-S-H on the Cs retention is the subject of debate in the literature-most studies found that Cs retention decreases with an increase of the Ca/Si ratio [7,11,14,15], but one study found the opposite [16].…”

Section: Introductionmentioning

confidence: 99%

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Thermodynamics, kinetics, and mechanics of cesium sorption in cement paste: A multiscale assessment

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Cesium-137 is a common radioactive byproduct found in nuclear spent fuel. Given its 30 year half life, its interactions with potential storage materials-such as cement paste-is of crucial importance. In this paper, simulations are used to establish the interaction of calcium silicate hydrates (C-S-H)-the main binding phase of cement paste-with Cs at the nano-and mesoscale. Different C-S-H compositions are explored, including a range of Ca/Si ratios from 1.0 to 2.0. These calculations are based on a set of 150 atomistic models, which qualitatively and quantitatively reproduce a number of experimentally measured features of C-S-H-within limits intrinsic to the approximations imposed by classical molecular dynamics and the steps followed when building the models. A procedure where hydrated Ca 2+ ions are swapped for Cs 1+ ions shows that Cs adsorption in the C-S-H interlayer is preferred to Cs adsorption at the nanopore surface when Cs concentrations are lower than 0.19 Mol/kg. Interlayer sorption decreases as the Ca/Si ratio increases. The activation relaxation technique nouveau is used to access timescales out of the reach of traditional molecular dynamics (MD). It indicates that characteristic diffusion time for Cs 1+ in the C-S-H interlayer is on the order of a few hours. Cs uptake in the interlayer has little impact on the elastic response of C-S-H. It leads to swelling of the C-S-H grains, but mesoscale calculations that access length scales out of the range of MD indicate that this leads to practically negligible expansive pressures for Cs concentrations relevant to nuclear waste repositories.