Effect of carbonates on the formation of magnesium silicate hydrates

Bernard, Ellina; Lothenbach, Barbara; Rentsch, Daniel; German, Alexander; Winnefeld, Frank

doi:10.1617/s11527-022-02018-3

Cited by 21 publications

(29 citation statements)

References 46 publications

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“…5. Additionally, higher Mg/Si ratios of up to 1.5, as in serpentine group minerals, can be observed in presence of carbonates [45], which were not reached otherwise, not even after a 3-yearequilibration at 20°C, or 2-year-equilibration at 50°C [41].…”

Section: Formation Of M-s-h Stability and Competition With Brucite Fo...mentioning

confidence: 96%

“…5. It was recently observed that dissolved carbonates also speed up the formation of M-S-H [69] by increasing the concentration of Mg due to the formation of aqueous complexes [45], as detailed in Fig. 5.…”

Section: Formation Of M-s-h Stability and Competition With Brucite Fo...mentioning

confidence: 97%

“…As much as M-S-H has similarities to phyllosilicates, it is rather a precursor of them presenting a variable composition and a variable structure (mixture of T:O and T:O.T), i.e. a solidsolution with Mg/Si ratios ranging from 0.75 to 1.5 [40,45]. A schematic sketch for the structure of M-S-H is given in Fig.…”

Section: Structure and Formation Of M-s-h Structure Of M-s-hmentioning

confidence: 99%

“…The uptake of Mg on exchangeable surface site is very small due to the low Mg concentrations in solution at pH values above 10.5 [41]. However, the presence of carbonates in solution leads to the formation of aqueous Mg-carbonate complexes, which increase the Mg concentration as well as the Mg uptake at the exchangeable surface sites [45].…”

Section: Structure and Formation Of M-s-h Structure Of M-s-hmentioning

confidence: 99%

“…In this letter, the thermodynamic modelling was carried out using the Gibbs free energy minimization program GEMSelektor [76] combined with the GEMS-PSI thermodynamic database [77] and the cemdata2018 database [78]. These databases were completed with thermodynamic data from [40,46,62] to describe the Ca and Al uptake in M-S-H: (C-)M-(A)S-H, the uptake of different anions in hydrotalcite from [79], the possible formation of (hydrated) magnesium carbonates [45] and Mg-phosphates phases and complexes from [80]. The modelling were used to predict the stability domains of M-S-H and M-A-S-H in the absence and presence of carbonates.…”

Section: Thermodynamic Databasesmentioning

confidence: 99%

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Research progress on magnesium silicate hydrate phases and future opportunities

Bernard

2022

RILEM Tech Lett

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This short letter summaries the latest research on the structure and thermodynamic modelling of the magnesium silicate hydrates (M-S-H) phases. M-S-H structure is comparable to hydrated clays, with a smaller and rounder microstructures compared to clay platelets. Similar to clay minerals, M-S-H can incorporate ions such as aluminium and hydrated exchangeable cations to compensate the negative surface charge. This fundamental understanding of M-S-H structure allowed to develop structure-based thermodynamic models, which can further help to optimise the conditions for M-S-H formation and its use as cementitious materials. Optimized binders containing M-S-H have the advantages of presenting: i) good mechanical properties, ii) dense microstructure and potentially good resistances to leaching and iii) low pH values. These types of binders could therefore be used for cement products with non-steel reinforcement, for the encapsulation of specific wastes, for products containing natural fibres or for the clay stabilisation, etc.

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Section: Formation Of M-s-h Stability and Competition With Brucite Fo...mentioning

confidence: 96%

Section: Formation Of M-s-h Stability and Competition With Brucite Fo...mentioning

confidence: 97%

Section: Structure and Formation Of M-s-h Structure Of M-s-hmentioning

confidence: 99%

Section: Structure and Formation Of M-s-h Structure Of M-s-hmentioning

confidence: 99%

Section: Thermodynamic Databasesmentioning

confidence: 99%

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Research progress on magnesium silicate hydrate phases and future opportunities

Bernard

2022

RILEM Tech Lett

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Low‐CO₂ cements based on magnesium oxide / hydromagnesite blends – hydration mechanism and mechanical properties

Winnefeld,

German,

Lura

et al. 2023

ce papers

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Binders based on blends of reactive magnesia and hydromagnesite are low‐CO2 or even carbon‐negative cements in case the MgO is generated from magnesium silicates or Mg‐containing brines. When MgO is hydrated with water alone, a well crystalline brucite forms, but no measurable strength is developing. In the presence of hydromagnesite, the hydration of MgO is accelerated and the hydrate assemblage is changed. A poorly‐crystalline brucite containing some carbonate is the main hydration product. Furthermore, a kind of “gel‐water” is observed, which is lost at temperatures above 40‐60°C. This brucite‐like phase is responsible for strength formation in MgO‐hydromagnesite blends. After 28 days, a mortar compressive strength is reached similar to the one of a Portland cement of strength class 32.5.

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MgO‐based binders

Lothenbach,

Bernard,

German

et al. 2023

ce papers

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To limit global temperature rise to below 2°C, we need to radically and rapidly change the way we build and use materials, since construction is responsible for 20‐40% of industrial CO2 emissions. Magnesium carbonate‐based cements have the potential to become a major carbon sink in construction industry, as CO2 will not be emitted during their production, but CO2 will rather be bound during hardening. Two different reaction mechanisms lead to setting and hardening of such HMC cements: i) hydration of MgO‐Mg‐carbonate, also in blends with silica and other mineral additions, in the presence of water or salt solutions (such as sodium bicarbonate solution) at ambient conditions or ii) carbonation hardening of MgO‐based systems at increased CO2 partial pressure and/or at increased temperatures.However, the utilization of hydrated magnesium carbonate and magnesium silicate cements is currently hampered by the lack of systematic experiments and of fundamental understanding of the factors affecting the hardening process, mechanical properties, long‐term behavior and durability. In particular, the role of temperature, relative humidity and addition of supplementary cementitious materials and/or industrial by‐products has not been systematically investigated. We need knowledge both on the practical side through systematic experiments with pastes, mortars and concretes as well as on a fundamental level through solubility and sorption experiments and thermodynamic modelling. In addition, reaction kinetics need to be optimized as well as the early formation of the preferred phases (stability enhancement) to develop efficient HMC cements for construction. Due to the socio‐economic relevance of cement and concrete, the impact of such “carbon”‐negative cements may go beyond a purely scientific one and lead to technological breakthroughs to the benefit of environment and society.

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Effect of carbonates on the formation of magnesium silicate hydrates

Cited by 21 publications

References 46 publications

Research progress on magnesium silicate hydrate phases and future opportunities

Research progress on magnesium silicate hydrate phases and future opportunities

Low‐CO₂ cements based on magnesium oxide / hydromagnesite blends – hydration mechanism and mechanical properties

MgO‐based binders

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Effect of carbonates on the formation of magnesium silicate hydrates

Cited by 21 publications

References 46 publications

Research progress on magnesium silicate hydrate phases and future opportunities

Research progress on magnesium silicate hydrate phases and future opportunities

Low‐CO2 cements based on magnesium oxide / hydromagnesite blends – hydration mechanism and mechanical properties

MgO‐based binders

Contact Info

Product

Resources

About

Low‐CO₂ cements based on magnesium oxide / hydromagnesite blends – hydration mechanism and mechanical properties