Evaluation of Sorption Behavior of Iodide Ions on Calcium Silicate Hydrate and Hydrotalcite

2015 ◽  
Vol 1744 ◽  
pp. 29-34
Author(s):  
Taiji Chida ◽  
Jun Furuya ◽  
Yuichi Niibori ◽  
Hitoshi Mimura
Keyword(s):  
Calcium Silicate ◽  
Calcium Silicate Hydrate ◽  
Solid Phase ◽  
Pure Water ◽  
Weight Ratio ◽  
Cementitious Materials ◽  
Sorption Behavior ◽  
Nacl Solution ◽  
Iodide Ions ◽  
Engineered Barriers

ABSTRACTThe migration retardation of anionic radionuclides, notably I-129, in radioactive waste repositories is one of the most critical factors for improving the performance of engineered barriers. To gain more fundamental knowledge required to make such improvements, this study examined the sorption behavior of iodide ions on calcium silicate hydrate (CSH) and hydrotalcite (HT), which act as anion exchangers. CSH was synthesized using CaO and fumed silica, with Ca/Si molar ratios ranging from 0.4 to 1.6. The weight ratio of CSH to HT was 1.0. These solid samples were immersed for 14 days in a 30 mL sample of pure water or 0.6 M NaCl solution, each of which contained 0.5 mM iodide ions with a given liquid/solid weight ratio (10, 15, or 20). Raman spectroscopy studies indicated that the structures of CSH and HT were maintained during the hydration of the solid phase and the sorption of iodide ions. The distribution coefficients for the sorption of iodide ions on CSH and HT ranged from 6 to 13 L/kg for pure water and from 1 to 2 L/kg for NaCl solution. These retardation effects for iodide ions would contribute toward improving the performance of the repository system as most conventional safety assessments assume that iodide ions hardly sorb on engineered barriers such as cementitious materials.

Mechanism of aluminium incorporation into C–S–H from ab initio calculations

2014 ◽  
Vol 2 (10) ◽  
pp. 3477-3483 ◽  
Author(s):  
Luís Pegado ◽  
Christophe Labbez ◽  
Sergey V. Churakov
Keyword(s):  
Ab Initio Calculations ◽  
Ab Initio ◽  
Calcium Silicate ◽  
Calcium Silicate Hydrate ◽  
Cementitious Materials ◽  
Al Substitution

Al substitution in calcium silicate hydrate (C–S–H) in novel, low CO2 cementitious materials takes place in bridging tetrahedral positions only.

Micromechanical Properties of Calcium Silicate Hydrate

2013 ◽  
Vol 539 ◽  
pp. 75-79
Author(s):  
Wu Yao ◽  
Li He
Keyword(s):  
Fly Ash ◽  
Reaction Zone ◽  
Calcium Silicate ◽  
Calcium Silicate Hydrate ◽  
Cement Hydration ◽  
Cementitious Materials ◽  
Pozzolanic Reaction ◽  
Indentation Modulus ◽  
Micromechanical Properties ◽  
Secondary Hydration

The indentation modulus of several cementitious materials is discussed with the assumption that the C-S-H gel is an aggregation of precipitated, colloidal-sized particles. At least two kinds of structurally distinct but compositional similar phases are found existent during the hydration process. In addition, the C-S-H originated from the pozzolanic reaction of fly ash is found to be the same to that of cement hydration in micromechanical properties; however, the C-S-H gel formed from the secondary hydration is inclined to develop into high density packing configuration, due to the limitation of reaction zone available.

scholarly journals Investigations on the Interaction of EDTA with Calcium Silicate Hydrate and Its Impact on the U(VI) Sorption

Coatings ◽  
2021 ◽  
Vol 11 (9) ◽  
pp. 1037
Author(s):  
Eleni Maragkou ◽  
Ioannis Pashalidis
Keyword(s):  
Calcium Silicate ◽  
Calcium Silicate Hydrate ◽  
Solid Phase ◽  
Alpha Spectroscopy ◽  
Ambient Atmosphere ◽  
Ambient Conditions ◽  
Kd Values ◽  
Edta Complexes ◽  
Langmuir Isotherm Model ◽  
Phase Characterization

The interaction of EDTA with calcium silicate hydrate (C-S-H) and its impact on the sorption of U(VI) by C-S-H in the presence of EDTA at varying concentrations has been investigated under N2 and ambient atmosphere. The solid phase characterization was performed by FTIR, XRD and TGA measurements and the uranium concentration in solution has been determined by alpha-spectroscopy. At increased EDTA concentrations ([EDTA] > 0.1 M) calcium is complexed and extensively extracted from the solid resulting in a quantitative dissolution of the Ca(OH)2 phase and deterioration of C-S-H. At lower EDTA concentrations ([EDTA] ≤ 0.01 M), EDTA is sorbed into the solid phase and the associated adsorption capacity (qmax = 0.67 mol/kg) has been evaluated by fitting the corresponding data with the Langmuir isotherm model. The incorporation of EDTA in the C-S-H matrix was corroborated by FTIR, XRD and TGA measurements. Regarding the effect of EDTA on the U(VI) sorption by C-S-H, evaluation of the experimental data reveal a significant decrease of the Kd values in the presence of EDTA most probably due to the stabilization of U(VI) in the form of U(VI)-EDTA complexes in solution. Under ambient conditions a further decrease of the Kd values is observed because of the formation of U(VI)-carbonato complexes related to CO2 dissolution and hydrolysis.

Xonotlite and Hillebrandite as Model Compounds for Calcium Silicate Hydrate Seeding in Cementitious Materials

2020 ◽  
pp. 036119812094320
Author(s):  
Elisabeth John ◽  
Christian Lehmann ◽  
Dietmar Stephan
Keyword(s):  
Calcium Silicate ◽  
Calcium Silicate Hydrate ◽  
Model Compound ◽  
Hydration Product ◽  
Cementitious Materials ◽  
Nucleation Site ◽  
Hydration Products ◽  
Sem Images ◽  
Pit Formation ◽  
Nanoparticle Additives

The demand for more environmentally friendly cement with no disadvantages in relation to hydration activity has led to the development of various additives to accelerate cement hydration. As calcium silicate hydrate (C-S-H) is the major hydration product of cement and is responsible for its mechanical properties, it plays an outstanding role in the discussion of nanoparticle additives. Nevertheless, the investigation of its mechanism of action is complicated by the similarity of its properties to those of the C-S-H that forms as an initial hydration product. Crystalline C-S-H phases, on the other hand, can be easily distinguished from the original hydration products, which makes them a valuable model compound for studying the mechanisms of nucleation seeding in cementitious materials. In this paper, the effect of crystalline types of C-S-H as nucleation seeds are presented. Xonotlite and hillebrandite were thoroughly characterized using nuclear magnetic resonance, X-ray diffractometry (XRD), scanning electron microscopy (SEM), and infrared spectroscopy (IR) and were then used as an admixture for alite pastes. Low-vacuum SEM images of the hydrated pastes revealed that xonotlite can significantly promote the visible etch pit formation on C3S clinker particles, which was not found to be true for hillebrandite. Whether the phases act as a nucleation site is assumed to be strongly dependent on the mineralogy: hillebrandite appeared to be heavily overgrown, but xonotlite did not show any hydration products on its surfaces after the same hydration time of up to 24 h. The diverse effect of the minerals was confirmed by the accelerating behavior in isothermal heat flow calorimetry and by XRD.

Deposition of Calcium-Silicate-Hydrate Gel on Rough Surface of Granite from Calcium-rich Highly Alkaline Plume

2012 ◽  
Vol 1475 ◽  
Author(s):  
Yuichi Niibori ◽  
Kyo Komatsu ◽  
Hitoshi Mimura
Keyword(s):  
Rough Surface ◽  
Calcium Silicate ◽  
Calcium Silicate Hydrate ◽  
Pure Water ◽  
Flow Paths ◽  
Constant Flow Rate ◽  
Micro Flow ◽  
Ca Ions ◽  
Large Roughness ◽  
Materials Used

ABSTRACTCement-based materials used in the construction of the repository for high/low level radioactive wastes may produce a highly alkaline calcium-rich groundwater (plume). The Ca ions react with soluble silicic acid, depositing calcium-silicate-hydrate (CSH) gel on the surfaces of the groundwater flow-paths and decreasing the permeability of the bedrock. Such a decrement of permeability may play a role in retarding the migration of radionuclides. In this study, the deposition behavior in a fracture was experimentally examined by using a micro flow-cell consisting of silicon plate (including a slit (60 mm×5 mm, or 60 mm×2 mm)) and granite-chip. The initial equivalent-aperture based on the square law was estimated in the range of 26 μm to 45 μm from the flow test of pure water.In the experiments, a Ca(OH)2 solution of 6.36 mM (pH: 12.2 to12.5, including NaOH) was continuously injected into the flow system at a constant flow rate of 1 or 2 ml/h. The solution flowed on the surface of the granite-chip. In this study, we prepared two kinds of chips that differed in the treatment of the surface. One chip was roughly ground with #2000 sandpaper (hereinafter referred to as rough surface) and another was polished to mirror-like surface. As a result, on the rough surface the deposits of CSH gel appeared along flow-channels across mineral grain-boundaries, while the deposits on the mirror-like surface were relatively uniform. Furthermore, the permeability in the case of rough surface became smaller than that in the case of mirror-like surface, showing the repeats of rapid decrement and increment due to the relatively large roughness of the surface. In order to estimate the decrement degrees of permeability, a simple, one-dimensional mathematical model is proposed in this study.

scholarly journals Ionic conductive and photocatalytic properties of cementitious materials: calcium silicate hydrate and calcium aluminoferrite

2020 ◽  
Vol 8 (30) ◽  
pp. 15157-15166
Author(s):  
Masahiro Nagao ◽  
Kazuyo Kobayashi ◽  
Yongcheng Jin ◽  
Ippei Maruyama ◽  
Takashi Hibino
Keyword(s):  
Photocatalytic Activity ◽  
Calcium Silicate ◽  
Calcium Silicate Hydrate ◽  
Concrete Structures ◽  
Cementitious Materials ◽  
Ion Conductivity ◽  
Photocatalytic Properties ◽  
Calcium Aluminoferrite ◽  
The Stability

Ion conductivity of C-S-H and photocatalytic activity of C4AF for the stability of concrete structures and the functionality of concrete surfaces.

scholarly journals Effect of Water on the Dynamic Tensile Mechanical Properties of Calcium Silicate Hydrate: Based on Molecular Dynamics Simulation

Materials ◽  
2019 ◽  
Vol 12 (17) ◽  
pp. 2837 ◽  
Author(s):  
Jikai Zhou ◽  
Yuanzhi Liang
Keyword(s):  
Mechanical Properties ◽  
Molecular Dynamics ◽  
Water Content ◽  
Calcium Silicate ◽  
Calcium Silicate Hydrate ◽  
Cementitious Materials ◽  
Constitutive Relationship ◽  
Degree Of Saturation ◽  
Strain Rates ◽  
Effect Of Water

To study the effect of water on the dynamic mechanical properties of calcium silicate hydrate (C–S–H) at the atomic scale, the molecular dynamics simulations were performed in uniaxial tension with different strain rates for C–S–H with a degree of saturation from 0% to 100%. Our calculations demonstrate that the dynamic tensile mechanical properties of C–S–H decrease with increasing water content and increase with increasing strain rates. With an increase in the degree of saturation, the strain rate sensitivity of C–S–H tends to increase. According to Morse potential function, the tensile stress-strain relationship curves of C–S–H are decomposed and fitted, and the dynamic tensile constitutive relationship of C–S–H considering the effect of water content is proposed. This reveals the strain rate effect of the cementitious materials with different water content from molecular insights, and the dynamic constitutive relationship obtained in this paper is necessary to the modelling of cementitious materials at the meso-scale.

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