The Experts below are selected from a list of 5100 Experts worldwide ranked by ideXlab platform
Gaurav Sant - One of the best experts on this subject based on the ideXlab platform.
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Temperature-Induced Aggregation in Portlandite Suspensions.
Langmuir : the ACS journal of surfaces and colloids, 2020Co-Authors: Sharu Bhagavathi Kandy, Mathieu Bauchy, Iman Mehdipour, Narayanan Neithalath, Edward J. Garboczi, Samanvaya Srivastava, Torben Gaedt, Gaurav SantAbstract:Temperature is well known to affect the aggregation behavior of colloidal suspensions. This paper elucidates the temperature dependence of the rheology of Portlandite (calcium hydroxide: Ca(OH)2) s...
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How Microstructure and Pore Moisture Affect Strength Gain in Portlandite-Enriched Composites That Mineralize CO2
ACS Sustainable Chemistry & Engineering, 2019Co-Authors: Iman Mehdipour, Gabriel D Falzone, Erika Callagon La Plante, Dante A Simonetti, Narayanan Neithalath, Gaurav SantAbstract:Binders containing Portlandite (Ca(OH)2) can take up carbon dioxide (CO2) from dilute flue gas streams (
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how microstructure and pore moisture affect strength gain in Portlandite enriched composites that mineralize co2
ACS Sustainable Chemistry & Engineering, 2019Co-Authors: Iman Mehdipour, Gaurav Sant, Gabriel D Falzone, Erika Callagon La Plante, Dante A Simonetti, Narayanan NeithalathAbstract:Binders containing Portlandite (Ca(OH)2) can take up carbon dioxide (CO2) from dilute flue gas streams (<15% CO2, v/v), thereby forming carbonate compounds with binding attributes. While the carbonation of Portlandite particulates is straightforward, it remains unclear how CO2 transport into monoliths is affected by microstructure and pore moisture content. Therefore, this study elucidates the influences of pore saturation and CO2 diffusivity on the carbonation kinetics and strength evolution of Portlandite-enriched composites (“mortars”). To assess the influences of microstructure, composites hydrated to different extents and conditioned to different pore saturation levels (Sw) were exposed to dilute CO2. First, reducing saturation increases the gas diffusivity and carbonation kinetics so long as saturation exceeds a critical value (Sw,c ≈ 0.10) independent of microstructural attributes. Second, careful analysis reveals that both traditional cement hydration and carbonation offer similar levels of streng...
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direct carbonation of ca oh 2 using liquid and supercritical co2 implications for carbon neutral cementation
Industrial & Engineering Chemistry Research, 2015Co-Authors: Kirk Vance, Gabriel Falzone, Isabella Pignatelli, Magdalena Balonis, Mathieu Bauchy, Gaurav SantAbstract:By invoking analogies to lime mortars of times past, this study examines the carbonation of Portlandite (Ca(OH)2) by carbon dioxide (CO2) in the liquid and supercritical states as a potential route toward CO2-neutral cementation. Portlandite carbonation is noted to be rapid; e.g., >80% carbonation of Ca(OH)2 is achieved in 2 h upon contact with liquid CO2 at ambient temperatures, and it is only slightly sensitive to the effects of temperature, pressure, and the state of CO2 over the range of 6 MPa ≤ p ≤ 10 MPa and 8 °C ≤ T ≤ 42 °C. Additional studies suggest that the carbonation of anhydrous ordinary portland cement is slower and far less reliable than that of Portlandite. Although cementation is not directly assessed, detailed scanning electron microscopy (SEM) examinations of carbonated microstructures indicate that the carbonation products formed encircle and embed sand grains similar to that observed in lime mortars. The outcomes suggest innovative directions for “carbon-neutral cementation.”
Janez Perko - One of the best experts on this subject based on the ideXlab platform.
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a new concept for pore scale precipitation dissolution modelling in a lattice boltzmann framework application to Portlandite carbonation
Applied Geochemistry, 2020Co-Authors: Anna Varzina, Sanheng Liu, Diederik Jacques, Özlem Cizer, Janez PerkoAbstract:Abstract Modelling of combined dissolution-precipitation at the pore scale requires the conceptualization of mineral precipitation and crystal growth, the formation of a protective diffusive layer by precipitants and slow reaction kinetics that are all coupled with alterations of the microstructure. In this work, we propose an improved approach for handling these challenges in a pore-scale coupled reactive transport model and apply it to Portlandite carbonation. The model combines mineral geometry update as a consequence of dissolution-precipitation reactions during diffusive transport through a saturated porous medium, thermodynamic equilibrium chemistry and dissolution kinetics. Transport of ions is calculated by the lattice Boltzmann transport solver YANTRA. Transport and reaction processes are incorporated at different spatial length scales with the multilevel approach, i.e. mixed liquid-solid nodes in a pore-scale model, which accounts for processes at scales below the model spatial resolution. Instead of defining arbitrary values such as threshold or residual porosities to initiate or halt precipitation, information on crystal shapes, packing and solubility in nano-pores based on interfacial surface energy is used to control precipitation. Additionally, the sensitivity study has been performed on model parameters such as Portlandite dissolution kinetics, interfacial surface energy, calcite crystal size, CO2 partial pressure on the rate of carbonation and on the calcite layer properties such as residual porosity and thickness. From the comparison between the modelled calcite growth and the experimental data it has been found that low diffusivity of calcite layer decreases the effect of Portlandite dissolution kinetics rate in case of carbonation and diminishes the effect of CO2 partial pressure. Also differences in the structure of the calcite layer were observed for carbonation of Portlandite at low and high CO2 partial pressures.
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A new concept for pore-scale precipitation-dissolution modelling in a lattice Boltzmann framework – Application to Portlandite carbonation
'Elsevier BV', 2020Co-Authors: Varzina Anna, Sanheng Liu, Cizer Ozlem, Diederik Jacques, Janez PerkoAbstract:Modelling of combined dissolution-precipitation at the pore scale requires the conceptualization of mineral precipitation and crystal growth, the formation of a protective diffusive layer by precipitants and slow reaction kinetics that are all coupled with alterations of the microstructure. In this work, we propose an improved approach for handling these challenges in a pore-scale coupled reactive transport model and apply it to Portlandite carbonation. The model combines mineral geometry update as a consequence of dissolution-precipitation reactions during diffusive transport through a saturated porous medium, thermodynamic equilibrium chemistry and dissolution kinetics. Transport of ions is calculated by the lattice Boltzmann transport solver YANTRA. Transport and reaction processes are incorporated at different spatial length scales with the multilevel approach, i.e. mixed liquid-solid nodes in a pore-scale model, which accounts for processes at scales below the model spatial resolution. Instead of defining arbitrary values such as threshold or residual porosities to initiate or halt precipitation, information on crystal shapes, packing and solubility in nano-pores based on interfacial surface energy is used to control precipitation. Additionally, the sensitivity study has been performed on model parameters such as Portlandite dissolution kinetics, interfacial surface energy, calcite crystal size, CO2 partial pressure on the rate of carbonation and on the calcite layer properties such as residual porosity and thickness. From the comparison between the modelled calcite growth and the experimental data it has been found that low diffusivity of calcite layer decreases the effect of Portlandite dissolution kinetics rate in case of carbonation and diminishes the effect of CO2 partial pressure. Also differences in the structure of the calcite layer were observed for carbonation of Portlandite at low and high CO2 partial pressures.status: publishe
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A new concept for pore-scale precipitation-dissolution modelling in a lattice Boltzmann framework ─ Application to Portlandite carbonation
Applied Geochemistry, 2020Co-Authors: Anna Varzina, Sanheng Liu, Diederik Jacques, Özlem Cizer, Janez PerkoAbstract:Abstract Modelling of combined dissolution-precipitation at the pore scale requires the conceptualization of mineral precipitation and crystal growth, the formation of a protective diffusive layer by precipitants and slow reaction kinetics that are all coupled with alterations of the microstructure. In this work, we propose an improved approach for handling these challenges in a pore-scale coupled reactive transport model and apply it to Portlandite carbonation. The model combines mineral geometry update as a consequence of dissolution-precipitation reactions during diffusive transport through a saturated porous medium, thermodynamic equilibrium chemistry and dissolution kinetics. Transport of ions is calculated by the lattice Boltzmann transport solver YANTRA. Transport and reaction processes are incorporated at different spatial length scales with the multilevel approach, i.e. mixed liquid-solid nodes in a pore-scale model, which accounts for processes at scales below the model spatial resolution. Instead of defining arbitrary values such as threshold or residual porosities to initiate or halt precipitation, information on crystal shapes, packing and solubility in nano-pores based on interfacial surface energy is used to control precipitation. Additionally, the sensitivity study has been performed on model parameters such as Portlandite dissolution kinetics, interfacial surface energy, calcite crystal size, CO2 partial pressure on the rate of carbonation and on the calcite layer properties such as residual porosity and thickness. From the comparison between the modelled calcite growth and the experimental data it has been found that low diffusivity of calcite layer decreases the effect of Portlandite dissolution kinetics rate in case of carbonation and diminishes the effect of CO2 partial pressure. Also differences in the structure of the calcite layer were observed for carbonation of Portlandite at low and high CO2 partial pressures.
Wayne C. Shanks - One of the best experts on this subject based on the ideXlab platform.
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oxygen isotope fractionation in the Portlandite water and brucite water systems from 125 to 450 c 50 mpa
Geochimica et Cosmochimica Acta, 2015Co-Authors: Peter J. Saccocia, Jeffrey S. Seewald, Wayne C. ShanksAbstract:Abstract Equilibrium oxygen isotope fractionation factors were determined for the Portlandite–water and brucite–water systems from 125 to 425 °C, 50 MPa using the partial exchange technique. Reagent grade cryptocrystalline Ca(OH)2 and amorphous Mg(OH)2 were reacted with three waters having different initial δ18O compositions. Isotope exchange occurred via recrystallization with exchange varying from 40% to 95% at 200 to 425 °C, respectively. Equilibrium 18O brucite–water fractionation factors (103lnα) increase from −4.7 ± 3.5‰ at 200 °C to −3.5 ± 2.5‰ at 425 °C. These data connect smoothly with previous experimental calibrations at lower and higher temperatures to define a single function valid from 15 to 450 °C, as follows: 10 3 ln α brucite - water = 4.39 × 10 6 T 2 - 16.95 × 10 3 T + 11.19 where T is temperature in Kelvin. These results confirm the existence of a broad minimum in the fractionation factor for brucite at ∼250 °C. The equilibrium 18O fractionation factor for Portlandite–water varies from −11.1 ± 2.7‰ at 125 °C to −6.6 ± 0.1‰ at 425 °C, and can be described by the following function: 10 3 ln α Portlandite - water = 5.61 × 10 6 T 2 - 26.29 × 10 3 T + 19.72 where T is temperature in Kelvin. These experimental results indicate that brucite favors 18O relative to Portlandite with brucite–Portlandite fractionation decreasing from 8‰ to 3‰ from 125 to 425 °C. A significant temperature dependent cation mass effect is therefore indicated for cation–OH bonds in hydroxide minerals. The observed fractionation is consistent with quantum theory which predicts that bonds with less massive cations have higher vibrational frequencies and will display a relative affinity for 18O to stabilize the structure. Brucite–Portlandite 18O fractionation predicted using the increment method is extremely small, opposite in sign (−0.1‰ to −0.2‰), and shows very little dependence on temperature, in poor agreement with the experimental calibration. This indicates that the method does not adequately account for the effect of cation mass on 18O fractionation within hydroxide minerals. It is suggested that cation-specific parameters within the increment method could be fit to the experimental calibrations reported here to improve prediction of fractionation factors for hydroxides and hydroxyl-bearing aluminosilicates, particularly at low temperate where the cation-mass effect is more significant.
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Oxygen isotope fractionation in the Portlandite–water and brucite–water systems from 125 to 450 °C, 50 MPa
Geochimica et Cosmochimica Acta, 2015Co-Authors: Peter J. Saccocia, Jeffrey S. Seewald, Wayne C. ShanksAbstract:Abstract Equilibrium oxygen isotope fractionation factors were determined for the Portlandite–water and brucite–water systems from 125 to 425 °C, 50 MPa using the partial exchange technique. Reagent grade cryptocrystalline Ca(OH)2 and amorphous Mg(OH)2 were reacted with three waters having different initial δ18O compositions. Isotope exchange occurred via recrystallization with exchange varying from 40% to 95% at 200 to 425 °C, respectively. Equilibrium 18O brucite–water fractionation factors (103lnα) increase from −4.7 ± 3.5‰ at 200 °C to −3.5 ± 2.5‰ at 425 °C. These data connect smoothly with previous experimental calibrations at lower and higher temperatures to define a single function valid from 15 to 450 °C, as follows: 10 3 ln α brucite - water = 4.39 × 10 6 T 2 - 16.95 × 10 3 T + 11.19 where T is temperature in Kelvin. These results confirm the existence of a broad minimum in the fractionation factor for brucite at ∼250 °C. The equilibrium 18O fractionation factor for Portlandite–water varies from −11.1 ± 2.7‰ at 125 °C to −6.6 ± 0.1‰ at 425 °C, and can be described by the following function: 10 3 ln α Portlandite - water = 5.61 × 10 6 T 2 - 26.29 × 10 3 T + 19.72 where T is temperature in Kelvin. These experimental results indicate that brucite favors 18O relative to Portlandite with brucite–Portlandite fractionation decreasing from 8‰ to 3‰ from 125 to 425 °C. A significant temperature dependent cation mass effect is therefore indicated for cation–OH bonds in hydroxide minerals. The observed fractionation is consistent with quantum theory which predicts that bonds with less massive cations have higher vibrational frequencies and will display a relative affinity for 18O to stabilize the structure. Brucite–Portlandite 18O fractionation predicted using the increment method is extremely small, opposite in sign (−0.1‰ to −0.2‰), and shows very little dependence on temperature, in poor agreement with the experimental calibration. This indicates that the method does not adequately account for the effect of cation mass on 18O fractionation within hydroxide minerals. It is suggested that cation-specific parameters within the increment method could be fit to the experimental calibrations reported here to improve prediction of fractionation factors for hydroxides and hydroxyl-bearing aluminosilicates, particularly at low temperate where the cation-mass effect is more significant.
Barbara Lothenbach - One of the best experts on this subject based on the ideXlab platform.
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Effect of relative humidity on the carbonation rate of Portlandite, calcium silicate hydrates and ettringite
Cement and Concrete Research, 2020Co-Authors: Sarah Steiner, Barbara Lothenbach, Tilo Proske, Andreas Borgschulte, Frank WinnefeldAbstract:Abstract The carbonation of Portlandite, calcium silicate hydrate (C-S-H), and ettringite was investigated at 57% RH and 91% RH using X-ray diffraction, thermogravimetric analysis, infrared spectroscopy, and the phenolphthalein spray test. The experiments show that the carbonation of Portlandite, ettringite, and C-S-H with Ca/Si = 0.7 is significantly faster at 91% RH than at 57% RH. Little effect of RH is observed for C-S-H with higher Ca/Si. Portlandite and C-S-H with Ca/Si = 0.7 carbonate only partially at 57% RH; complete carbonation is observed if the relative humidity is increased to 91% RH. In contrast, the carbonation of C-S-H with Ca/Si = 1.2 and 1.5 is complete at both relative humidities. The carbonation rate of C-S-H decreases with decreasing Ca/Si ratio, both at 57% and 91%RH. Carbonation at 57% RH promotes the formation of vaterite and aragonite over calcite; the precipitation of amorphous calcium carbonate is observed for C-S-H with Ca/Si = 0.7.
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alkali silica reaction the influence of calcium on silica dissolution and the formation of reaction products
Journal of the American Ceramic Society, 2011Co-Authors: Andreas Leemann, Frank Winnefeld, Gwenn Le Saout, Daniel Rentsch, Barbara LothenbachAbstract:In a model system for alkali―silica reaction consisting of microsilica, Portlandite (0-40 mass%), and 1M alkaline solutions (NaOH, KOH), the influence of calcium on silica dissolution and on the formation of reaction products is investigated. The reaction and its products are characterized using calorimetry, X-ray diffraction, thermogravimetric analysis, nuclear magnetic resonance, desorption experiments, and pore solution analysis in combination with thermodynamic modeling. Silica dissolution proceeds until Portlandite is consumed due to the formation of C-S-H, and subsequently, saturation of dissolved silica in the alkaline solution is reached. As a result, the amount of dissolved silica increases with the increasing Portlandite content. Depending on the amount of Portlandite added, the reaction products show differences in the relative amounts of Q 1 , Q 2 , and Q 3 sites formed and in their average Ca/Si ratio. The ability of the reactions products to chemically bind water decreases with the decreasing relative amount of Q 3 sites and with the increasing Ca/Si ratio. However, the amount of physically bound water in the reaction products reaches a maximum value at a Ca/Si ratio between 0.20 and 0.30.
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Alkali–Silica Reaction: the Influence of Calcium on Silica Dissolution and the Formation of Reaction Products
Journal of the American Ceramic Society, 2010Co-Authors: Andreas Leemann, Frank Winnefeld, Gwenn Le Saout, Daniel Rentsch, Barbara LothenbachAbstract:In a model system for alkali―silica reaction consisting of microsilica, Portlandite (0-40 mass%), and 1M alkaline solutions (NaOH, KOH), the influence of calcium on silica dissolution and on the formation of reaction products is investigated. The reaction and its products are characterized using calorimetry, X-ray diffraction, thermogravimetric analysis, nuclear magnetic resonance, desorption experiments, and pore solution analysis in combination with thermodynamic modeling. Silica dissolution proceeds until Portlandite is consumed due to the formation of C-S-H, and subsequently, saturation of dissolved silica in the alkaline solution is reached. As a result, the amount of dissolved silica increases with the increasing Portlandite content. Depending on the amount of Portlandite added, the reaction products show differences in the relative amounts of Q 1 , Q 2 , and Q 3 sites formed and in their average Ca/Si ratio. The ability of the reactions products to chemically bind water decreases with the decreasing relative amount of Q 3 sites and with the increasing Ca/Si ratio. However, the amount of physically bound water in the reaction products reaches a maximum value at a Ca/Si ratio between 0.20 and 0.30.
F. Renard - One of the best experts on this subject based on the ideXlab platform.
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Growth of Nanosized Calcite through Gas−Solid Carbonation of Nanosized Portlandite under Anisobaric Conditions
Crystal Growth & Design, 2010Co-Authors: G. Montes-hernandez, D. Daval, R. Chiriac, F. RenardAbstract:The gas−solid carbonation of nanosized Portlandite was experimentally investigated using a static bed reactor under anisobaric conditions. The effects of initial CO2 pressure (10−40 bar), reaction temperature (30 and 60 °C), and relative humidity were investigated. Three steps of the carbonation process were determined: (1) instantaneous CO2 mineralization during CO2 injection period. From 25 to 40 wt % of initial Portlandite grains were transformed into calcite during the CO2 injection period (from 0.9 to 2 min). (2) Fast CO2 mineralization after gas injection period ( 95%). For this case, the mineralization of CO2 does not form a protective carbonate layer around the reacting particles of Portlandite as typically observed by other gas−solid carbonation methods. This method could be efficiently performed to produce nanosized calcite. Moreover, the separation of calcite particles from the fluid phase is most simple compared with precipitation methods. A kinetic pseudo-second-order model was satisfactorily used to describe the three CO2 mineralization steps except for the carbonation reaction initiated at 40 bar. In this latter case, a kinetic pseudo-first-order model was satisfactorily used; indicating that the slow CO2 mineralization step appears less significant during the carbonation process.
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Growth of Nanosized Calcite through Gas−Solid Carbonation of Nanosized Portlandite under Anisobaric Conditions
Crystal Growth and Design, 2010Co-Authors: G. Montes-hernandez, D. Daval, R. Chiriac, F. RenardAbstract:The gas−solid carbonation of nanosized Portlandite was experimentally investigated using a static bed reactor under anisobaric conditions. The effects of initial CO2 pressure (10−40 bar), reaction temperature (30 and 60 °C), and relative humidity were investigated. Three steps of the carbonation process were determined: (1) instantaneous CO2 mineralization during CO2 injection period. From 25 to 40 wt % of initial Portlandite grains were transformed into calcite during the CO2 injection period (from 0.9 to 2 min). (2) Fast CO2 mineralization after gas injection period (
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growth of nanosized calcite through gas solid carbonation of nanosized Portlandite under anisobaric conditions
Crystal Growth & Design, 2010Co-Authors: German Monteshernandez, D. Daval, R. Chiriac, F. RenardAbstract:The gas−solid carbonation of nanosized Portlandite was experimentally investigated using a static bed reactor under anisobaric conditions. The effects of initial CO2 pressure (10−40 bar), reaction temperature (30 and 60 °C), and relative humidity were investigated. Three steps of the carbonation process were determined: (1) instantaneous CO2 mineralization during CO2 injection period. From 25 to 40 wt % of initial Portlandite grains were transformed into calcite during the CO2 injection period (from 0.9 to 2 min). (2) Fast CO2 mineralization after gas injection period ( 95%). For this case, the mineralization of CO2 does not form a protective carbonate layer around the reacting particles of Portlandite as typically observed by other gas−solid carbonation methods. This method could be efficiently performed to produce nanosized calcite. Moreover, the separation of calcite particles from the fluid phase is most simple compared with precipitation methods. A kinetic pseudo-second-order model was satisfactorily used to describe the three CO2 mineralization steps except for the carbonation reaction initiated at 40 bar. In this latter case, a kinetic pseudo-first-order model was satisfactorily used; indicating that the slow CO2 mineralization step appears less significant during the carbonation process.
