Investigation of the carbonation mechanism of CH and C-S-H in terms of kinetics, microstructure changes and moisture properties

Morandeau, Antoine; Thiéry, Mickaël; Dangla, Patrick

doi:10.1016/j.cemconres.2013.11.015

Cited by 751 publications

(339 citation statements)

References 55 publications

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“…But if considering the carbonation of C-S-H, the effect of the carbonation on the porosity and microstructure of cement paste is still controversial. Carbonation of C-S-H has been studied by many authors (Zdeneˇk Sˇauman 1972, Black, Breen et al 2007, Morandeau, Thiery et al 2014. It agreed that a complex decalcification-polymerization process of the C-S-H and the formation of amorphous silica gel, see equation (2).…”

Section: Introductionmentioning

confidence: 94%

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Development of porosity of cement paste blended with supplementary cementitious materials after carbonation

2017

Construction and Building Materials

147

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Supplementary cementitious materials (SCMs) like fly ash (FA) and blast furnace slag (BFS) are normally used to replace parts of Ordinary Portland cement (OPC) to reduce the cost and CO 2 emission. Some consequences are the reduction of portlandite (CH) content and the formation of C-S-H with low Ca/Si ratio, due to pozzolanic reactions. It is known that carbonation of portlandite leads to a reduction in the porosity which is ascribed to the positive difference of molar volumes between CH and CaCO 3 . However, the influence on the porosity caused by the carbonation of C-S-H is still controversial. The molar volume change due to the carbonation of C-S-H depends on the properties of C-S-H (like Ca/Si ratio, water content) and the water remained in silica gel. Moreover, the decalcification of C-S-H with the Ca/Si ratio lower than 1.2 can cause more structure changes and shrinkage of C-S-H. During the carbonation of cement paste blended with SCMs, less portlandite but a relatively high amount of C-S-H with low Ca/Si ratio will be carbonated. The pore structure will evolve in a different way, comparing with Portland cement paste. Therefore, it's very important to figure out the pore structure development of cement paste blended with SCMs under carbonation.In this paper, the binary cement pastes (B70, blended with blast furnace slag, and F30, blended with fly ash) and ternary cement pastes (F10B54 and F30B30, blended with blast furnace slag and fly ash) are studied and compared with Portland cement paste. Mercury Intrusion Porosimetry (MIP) and nitrogen adsorption isotherm are used to determine the pore volume and size distribution of capillary pores and gel pores (2-37 nm), respectively. Thermogravimetric analysis (TGA) is used to determine the amounts of portlandite and CaCO 3 . The results show that the amount profiles of portlandite and CaCO 3 can be used as a more accurate method to study the carbonation in blended cement paste, comparing with the phenolphthalein test. Carbonation of most of the species of C-S-H results in the increase of the porosity of cement paste. CaCO 3 contributed by the carbonation of low Ca C-S-H is dominant in blended cement paste B70, F10B54 and F30B30. Both the total and effective capillary porosity increases in the above-mentioned paste after the carbonation. Moreover, total porosities of B70 and F10B54 increase with the increasing amount of C-S-H involving in carbonation. However, the increment of the total porosity of F30B30 decreases with the increasing amount of C-S-H being carbonated. Carbonation of C-S-H increases the volume and size of the small gel pore, and creates more capillary pores. This peculiar phenomenon is more evident for the mixture with a higher proportion of SCMs, like B70 and F30B30. The results reveal that the carbonation of C-S-H formed in pozzolanic reactions cause the increase of the total and capillary porosity in cement paste blended with SCMs, which will bring adverse effects on the durability of blended cement concrete exposed to the carbonation...

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Section: Introductionmentioning

confidence: 94%

“…From thermodynamic point of view, the carbonation of CH has a priority comparing with C-S-H (Glasser and Matschei 2007). However in experiments the initial rate of carbonation is quite similar (Morandeau, Thiery et al 2014). Therefore, the main carbonation reactions happened inside the concrete are as follows:…”

Section: Introductionmentioning

confidence: 99%

Development of porosity of cement paste blended with supplementary cementitious materials after carbonation

2017

Construction and Building Materials

147

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“…In the direct carbonation route steps (1) and (2) occur simultaneously and the rate and extent of carbonation depend on a number of factors such as the precursor composition and moisture saturation degree [24,25], but also on the carbonation conditions such as the CO 2 grade and pressure and the relative humidity [26,27]. Saturation degree and relative humidity play a key role in providing CO 2 access to the connected pore network.…”

Section: Carbonation Mechanismsmentioning

confidence: 99%

Carbonate-bonded construction materials from alkaline residues

Nielsen¹,

Baciocchi²,

Costa³

et al. 2017

RILEM Tech Lett

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Accelerated carbonation is a rapidly developing technology that is attracting attention as it uses CO 2 as a binder to make construction materials. Originally stemming from geochemical and environmental research into CO 2 sequestration or waste remediation, accelerated carbonation has been developed into a technology that enables to transform alkaline precursors into products that meet technical requirements for use as aggregates or shaped blocks. Alkaline precursors can be manufactured from primary resources or derived from industrial residues: a.o. metallurgical slags, incineration ashes and concrete recycling residues are prone to carbonate under controlled conditions. Moist carbonation of shaped Ca-silicate rich precursors at elevated curing temperature and CO 2 concentration or pressure has delivered the most promising results so far. This letter presents an overview of current accelerated carbonation approaches to make carbonate-bonded construction materials from alkaline residues. The general carbonation mechanism is explained and two application routes are exemplified: i.e. production of lightweight aggregates and compact blocks by accelerated moist carbonation.

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“…Data for molar volume of C-S-H is still scarce and it is supposed to be stoichiometry-dependent parameter. Recent experimental study (Morandeau et al 2014) showed that the molar volume of C-S-H is in direct proportion to Ca/Si ratio as:…”

Section: Evolution Of Porosity Due To Carbonationmentioning

confidence: 99%

Evolution of Microstructure and Transport Properties of Cement Pastes Due to Carbonation under a CO ₂ Pressure Gradient—A Modeling Approach

et al. 2015

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Most carbonation models only account for diffusion as the main transport mechanism rather than advection. Nevertheless, in the case of concrete used for underground waste disposal facilities, concrete may be subjected to a high hydrostatic pressure and the surrounding environment may contain a high dissolved CO 2 concentration. Therefore, a combination of diffusion and advection should be taken into account. This is also the case in accelerated carbonation where a high CO 2 pressure gradient is applied in which advection in the gas phase has a significant contribution to the carbonation process. This study aims at developing a model to predict the evolution of the microstructure and transport properties of cement pastes due to carbonation under accelerated conditions in which a pressure gradient of pure CO 2 is applied. The proposed model is based on a macroscopic mass balance for carbon dioxide in gaseous and aqueous phases. Besides the prediction of the changes in transport properties (diffusivity, permeability), the model also enables to predict the changes in microstructure. Data from accelerated tests were used to validate the model. Preliminary verification with experimental results shows a good agreement.

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Investigation of the carbonation mechanism of CH and C-S-H in terms of kinetics, microstructure changes and moisture properties

Cited by 751 publications

References 55 publications

Development of porosity of cement paste blended with supplementary cementitious materials after carbonation

Development of porosity of cement paste blended with supplementary cementitious materials after carbonation

Carbonate-bonded construction materials from alkaline residues

Evolution of Microstructure and Transport Properties of Cement Pastes Due to Carbonation under a CO ₂ Pressure Gradient—A Modeling Approach

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Investigation of the carbonation mechanism of CH and C-S-H in terms of kinetics, microstructure changes and moisture properties

Cited by 751 publications

References 55 publications

Development of porosity of cement paste blended with supplementary cementitious materials after carbonation

Development of porosity of cement paste blended with supplementary cementitious materials after carbonation

Carbonate-bonded construction materials from alkaline residues

Evolution of Microstructure and Transport Properties of Cement Pastes Due to Carbonation under a CO 2 Pressure Gradient—A Modeling Approach

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Product

Resources

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Evolution of Microstructure and Transport Properties of Cement Pastes Due to Carbonation under a CO ₂ Pressure Gradient—A Modeling Approach