Kinetic analysis of C-S-H growth on calcite

Scherer, George W.; Bellmann, F.

doi:10.1016/j.cemconres.2016.07.017

Cited by 34 publications

(47 citation statements)

References 14 publications

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“…Nonlinear regression of the C−S−H ideal solid solution model with the two end members given in Table 2 provides nearly as good an agreement with published solubility data as other solid solution models, and the solubility constants given in Table 3 are those that yield the minimum sum of squared residuals (SSR) for those compositions, as described fully in Reference [47]. The rate constants and form of the rate law for C−S−H growth,

\frac{d N_{CSH}}{d t} = k_{CSH} A_{CSH} {false(β_{Tot} - 1 false)}^{3}

are those shown to provide the closest agreement to recent experimental measurements of C−S−H growth on calcite crystals [44]. In Eq.…”

Section: Computer Simulationssupporting

confidence: 56%

“…HydratiCA does not attempt to explicitly model these individual globules, but considers a fundamental growth unit of C−S−H to include several clusters of these globules together with saturated intercluster pores. The intercluster porosity is assumed to be 70 % by volume and saturated with aqueous solution [44]. The water in the porosity is assumed to be available for further reactions, except for 2.2 formula units of physically adsorbed water per formula unit of SiO 2 in C−S−H [36].…”

Section: Computer Simulationsmentioning

confidence: 99%

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A critical comparison of 3D experiments and simulations of tricalcium silicate hydration

et al. 2017

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Advances in nano-computed X-ray tomography (nCT), nano X-ray fluorescence spectrometry (nXRF), and high-performance computing have enabled the first direct comparison between observations of three-dimensional nanoscale microstructure evolution during cement hydration and computer simulations of the same microstructure using HydratiCA. nCT observations of a collection of triclinic tricalcium silicate (CaSiO) particles reacting in a calcium hydroxide solution are reported and compared to simulations that duplicate, as nearly as possible, the thermal and chemical conditions of those experiments. Particular points of comparison are the time dependence of the solid phase volume fractions, spatial distributions, and morphologies. Comparisons made at 7 h of reaction indicate that the simulated and observed volumes of CaSiO consumed by hydration agree to within the measurement uncertainty. The location of simulated hydration product is qualitatively consistent with the observations, but the outer envelope of hydration product observed by nCT encloses more than twice the volume of hydration product in the simulations at the same time. Simultaneous nXRF measurements of the same observation volume imply calcium and silicon concentrations within the observed hydration product envelope that are consistent with Ca(OH) embedded in a sparse network of calcium silicate hydrate (C-S-H) that contains about 70 % occluded porosity in addition to the amount usually accounted as gel porosity. An anomalously large volume of Ca(OH) near the particles is observed both in the experiments and in the simulations, and can be explained as originating from the hydration of additional particles outside the field of view. Possible origins of the unusually large amount of observed occluded porosity are discussed.

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\frac{d N_{CSH}}{d t} = k_{CSH} A_{CSH} {false(β_{Tot} - 1 false)}^{3}

are those shown to provide the closest agreement to recent experimental measurements of C−S−H growth on calcite crystals [44]. In Eq.…”

Section: Computer Simulationssupporting

confidence: 56%

Section: Computer Simulationsmentioning

confidence: 99%

A critical comparison of 3D experiments and simulations of tricalcium silicate hydration

et al. 2017

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“…The derivation process of the dissolution rate of C‐S‐H is more complicated because (i) the solid phase is like a solid solution with end‐member activities each different from one, (ii) water is involved as a reactant and not just a catalyst in the overall reaction, and (iii) the surface area of C‐S‐H is difficult to measure in the saturated state. As a simplification, if the phase C‐S‐H is approximated as a stoichiometric solid with fixed composition (meaning that its activity in the standard state is equal to one by definition), and if the activity of water in pore solution is also approximated as one, the dissolution of C‐S‐H can be expressed as,

{normalC}_{x} {SH}_{y} + false(1 + x - y false) {normalH}_{2} O ⇌ x {Ca}^{2 +} + {normalH}_{3} {SiO}_{4}^{-} + false(2 x - 1 false) {OH}^{-},

and

{\overset{N}{true}}_{C - S - H} = k_{C - S - H}^{f} A_{C - S - H} {()(1 - \frac{Q_{normalC - normalS - normalH}}{K_{normaleq_normalC - normalS - normalH}})}^{3},

where

{\dot{N}}_{normalC - normalS - normalH}

is the net dissolution rate,

k_{normalC - normalS - normalH}^{f}

is the kinetic rate constant, A C‐S‐H is the surface area, Q C‐S‐H and K eq_C‐S‐H are the activity product and equilibrium activity product of C‐S‐H, respectively . Within the computational program developed in this study, C‐S‐H is not treated as a single stoichiometric phase, but as a solid solution consisting of multiple stoichiometric components (e.g.…”

Section: Conceptualizationmentioning

confidence: 99%

“…The dissolution rate for each component of C‐S‐H, and thus the overall C‐S‐H dissolution rate, can be calculated using Equation . For all components that form C‐S‐H, the same value of

k_{normalC - normalS - normalH}^{f}

was applied, and this value has been inferred experimentally to be approximately 1.5 × 10 −10 mol m −2 s −1 ; this value is within the range of rate constants determined for C‐S‐H by Trapote‐Barreira et al . Note that this inferred rate constant was measured experimentally when C‐S‐H is growing rather than dissolving, and an assumption was made that the kinetic rate constants are the same for dissolution as for growth.…”

Section: Conceptualizationmentioning

confidence: 99%

Creep and relaxation of cement paste caused by stress‐induced dissolution of hydrated solid components

Grasley

Bullard

et al. 2018

J Am Ceram Soc

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The creep and relaxation of cement paste caused by dissolving solid hydration products is evaluated in this work. According to the second law of thermodynamics, dissolution or precipitation of solid constituents may be altered by the change in stress/strain fields inside cement paste via alteration of the stress power or strain energy. Thus, it is hypothesized that stress‐induced dissolution can affect the overall creep/relaxation behavior of cement composites. A novel, fully coupled thermodynamic, mechanical, and microstructural model (TM2) that uses the finite element method was developed to predict the time‐evolving properties of cement paste under prescribed strains and to test the hypothesis. In the model, the strain energy was incorporated to accurately predict the effect of stress and strain fields on cement microstructure change. From the simulation results, depending on the stress/strain levels and the choice of the domain (over which the thermodynamic equilibrium is enforced), stress‐induced dissolution of solid constituents can lead to significant creep/relaxation.

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“…In the lateral direction (ie, parallel to the substrate's surface), the growth rate is isotropic; however, in the longitudinal direction (ie, perpendicular to the substrate's surface), the outward growth rate ( G out ) is double the rate in the lateral direction. Such anisotropy in product's growth has been implemented to mimic the actual geometry of C–S–H's early‐age growth, as observed in experiments . The temporal variation in growth rate is based on an implementation originally formulated by Bullard et al, and subsequently adopted in several studies, to capture changes in C–S–H's growth rate in relation to its supersaturation in the solution.…”

Section: Phase Boundary Nucleation and Growth Modelmentioning

confidence: 99%

Effect of particle size distribution of metakaolin on hydration kinetics of tricalcium silicate

Lapeyre

Kumar

2019

J Am Ceram Soc

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The focus of this study is to elucidate the role of particle size distribution (PSD) of metakaolin (MK) on hydration kinetics of tricalcium silicate (C3S–T1) pastes. Investigations were carried out utilizing both physical experiments and phase boundary nucleation and growth (pBNG) simulations. [C3S + MK] pastes, prepared using 8%mass or 30%mass MK, were investigated. Three different PSDs of MK were used: fine MK, with particulate sizes <20 µm; intermediate MK, with particulate sizes between 20 and 32 µm; and coarse MK, with particulate sizes >32 µm. Results show that the correlation between specific surface area (SSA) of MK's particulates and the consequent alteration in hydration behavior of C3S in first 72 hours is nonlinear and nonmonotonic. At low replacement of C3S (ie, at 8% mass), fine MK, and, to some extent, coarse MK act as fillers, and facilitate additional nucleation and growth of calcium silicate hydrate (C–S–H). When C3S replacement increases to 30% mass, the filler effects of both fine and coarse MK are reversed, leading to suppression of C–S–H nucleation and growth. Such reversal of filler effect is also observed in the case of intermediate MK; but unlike the other PSDs, the intermediate MK shows reversal at both low and high replacement levels. This is due to the ability of intermediate MK to dissolve rapidly—with faster kinetics compared to both coarse and fine MK—which results in faster release of aluminate [Al(OH)4−] ions in the solution. The aluminate ions adsorb onto C3S and MK particulates and suppress C3S hydration by blocking C3S dissolution sites and C–S–H nucleation sites on the substrates’ surfaces and suppressing the post‐nucleation growth of C–S–H. Overall, the results suggest that grinding‐based enhancement in SSA of MK particulates does not necessarily enhance early‐age hydration of C3S.

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Kinetic analysis of C-S-H growth on calcite

Cited by 34 publications

References 14 publications

A critical comparison of 3D experiments and simulations of tricalcium silicate hydration

A critical comparison of 3D experiments and simulations of tricalcium silicate hydration

Creep and relaxation of cement paste caused by stress‐induced dissolution of hydrated solid components

Effect of particle size distribution of metakaolin on hydration kinetics of tricalcium silicate

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