Impact of hydrated magnesium carbonate additives on the carbonation of reactive MgO cements

Unluer, Cise; Al‐Tabbaa, Abir

doi:10.1016/j.cemconres.2013.08.009

Cited by 258 publications

(130 citation statements)

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“…This paper is a discussion of two recent papers by Unluer & Al-Tabbaa [1,2] which analysed accelerated 9 carbonation of reactive MgO blocks. We suggest that the authors have incorrectly analysed key data, leading 10 to overstated claims of MgO carbonation.…”

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confidence: 99%

“…This graphic is 37 reproduced here as Figure 1, with our suggested peak assignments for their first set of XRD patterns overlaid 38 on the original data. The authors of [1] mis-assign the major calcite peak at PDF # 005-0586), 39 labelling it as nesquehonite and dypingite (both magnesium carbonate phases). Additional calcite reflections 40 confirming its presence in these samples.…”

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confidence: 99%

“…Two recently 17 published papers by Unluer and Al-Tabbaa [1, 2] have added to the body of literature on these cements, 18 studying the effect of hydrated magnesium carbonate (HMC) addition and curing conditions, respectively, on 19 the properties and structure of porous reactive MgO cement blocks exposed to accelerated carbonation 20 conditions. We will focus the discussion here on the first of these two papers, as the results presented in the 21 second are largely an extension of the first, and contain similar points requiring re-analysis.…”

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confidence: 99%

“…7 in [1]). This graphic is 37 reproduced here as Figure 1, with our suggested peak assignments for their first set of XRD patterns overlaid 38 on the original data.…”

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confidence: 99%

“…In the paper "Impact of hydrated magnesium carbonate additives on the carbonation of reactive MgO 29 cements" [1], the authors produce blocks containing natural aggregates, pulverised fuel ash (PFA) as filler, 30…”

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confidence: 99%

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A discussion of the papers “ Impact of hydrated magnesium carbonate additives on the carbonation of reactive MgO cements ” and “ Enhancing the carbonation of MgO cement porous blocks through improved curing conditions ”, by C. Unluer & A. Al-Tabbaa

Walling

Provis

2016

Cement and Concrete Research

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8This paper is a discussion of two recent papers by Unluer & Al-Tabbaa [1, 2] which analysed accelerated 9 carbonation of reactive MgO blocks. We suggest that the authors have incorrectly analysed key data, leading 10 to overstated claims of MgO carbonation. Based on reassignment of their X-ray diffraction data, it is proposed 11 that little MgO carbonation occurred in the samples discussed in those papers, with CaCO3 instead forming 12 during accelerated carbonation. We also draw attention to the thermodynamic instability of nesquehonite 13 under ambient conditions, which calls into question the long-term stability of these binders. 14 Discussion 15Cements containing reactive magnesia are of great interest as alternative binders, as they have been 16 proclaimed to embody potentially lower CO2 emissions during manufacture and service. Two recently 17 published papers by Unluer and Al-Tabbaa [1, 2] have added to the body of literature on these cements, 18 studying the effect of hydrated magnesium carbonate (HMC) addition and curing conditions, respectively, on 19 the properties and structure of porous reactive MgO cement blocks exposed to accelerated carbonation 20 conditions. We will focus the discussion here on the first of these two papers, as the results presented in the 21 second are largely an extension of the first, and contain similar points requiring re-analysis. 22In these papers the authors claim to carbonate MgO to form a range of magnesium carbonates which 23 constitute their binding phases; this is a key aspect of the 'green' credentials proposed for these alternative 24 cements. Unfortunately, we are unable to reach the same conclusions made by the authors, based on our 25 own analysis of the data presented in their papers. In our opinion, the scientific discussion in these two 26 papers is based upon poorly-assigned X-ray diffraction patterns, which have led to incorrect interpretations 27 of thermal analysis data, and consequently erroneous claims of high levels of carbonation. 28In the paper "Impact of hydrated magnesium carbonate additives on the carbonation of reactive MgO 29 cements" [1], the authors produce blocks containing natural aggregates, pulverised fuel ash (PFA) as filler, 30and MgO as the key anhydrous precursor, with hydrated magnesium carbonates (HMCs) added to some of 31 the mixes. The combination of hydration and carbonation is proposed to lead to the formation of additional 32 hydrated magnesium carbonates as binding phases, when cured under either natural or accelerated 33 carbonation conditions. The authors achieved some interesting strength data, exceeding 20 MPa in 34 compression in some instances, which shows that their methodology is of some interest. 35However, there are several apparent discrepancies in the peak assignments in the two XRD patterns used by 36 the authors to identify hydration products after accelerated carbonation (Fig. 7 in [1]). This graphic is 37 reproduced here as Figure 1, with our suggested peak assignments for their first set of XRD patt...

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confidence: 99%

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confidence: 99%

“…7 in [1]). This graphic is 37 reproduced here as Figure 1, with our suggested peak assignments for their first set of XRD patterns overlaid 38 on the original data.…”

mentioning

confidence: 99%

mentioning

confidence: 99%

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A discussion of the papers “ Impact of hydrated magnesium carbonate additives on the carbonation of reactive MgO cements ” and “ Enhancing the carbonation of MgO cement porous blocks through improved curing conditions ”, by C. Unluer & A. Al-Tabbaa

Walling

Provis

2016

Cement and Concrete Research

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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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Carbonation curing of industrial solid waste‐based aerated concretes

et al. 2019

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Mineral carbonation for concrete curing is a promising route to large‐scale CO2 sequestration and the economic production of building materials. In this work, the carbonation curing of a kind of lightweight concrete, aerated concrete, was comprehensively studied. Three typical industrial wastes – fly ash, blast furnace slag, and red mud – were employed to replace part of the cement and to reduce the carbon footprint of products. The effects of carbonation curing time, pressure, and water‐to‐solids ratio on the CO2 uptake and compressive strength were investigated. Aerated concrete with red mud showed the highest CO2 uptake capacity, followed by concrete with fly ash, and concrete with blast furnace slag. The main crystalline carbonation products, needle‐like calcite and rod‐like aragonite, were observed to be embedded in the surface of fly ash and blast‐furnace‐slag‐based specimens. The orderly structures of carbonated crystals, as well as the reduction of mesoscale porosity (< 50 nm), resulted in an enhancement of mechanical properties. For red‐mud‐based specimens, calcite crystals with the appearance of grains (smaller than 1μm) were formed due to deeper carbonation. The rapid growth of calcite grains may lead to cracks from inside red‐mud‐based specimens and cause a negative effect on mechanical properties. In terms of mechanical performance, the blast furnace slag specimens, after carbonation curing, exhibited the largest compressive strength of 7.3 MPa, which was over 197% higher than that of natural curing for the same duration. © 2019 Society of Chemical Industry and John Wiley & Sons, Ltd.

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Impact of hydrated magnesium carbonate additives on the carbonation of reactive MgO cements

Cited by 258 publications

References 29 publications

A discussion of the papers “ Impact of hydrated magnesium carbonate additives on the carbonation of reactive MgO cements ” and “ Enhancing the carbonation of MgO cement porous blocks through improved curing conditions ”, by C. Unluer & A. Al-Tabbaa

A discussion of the papers “ Impact of hydrated magnesium carbonate additives on the carbonation of reactive MgO cements ” and “ Enhancing the carbonation of MgO cement porous blocks through improved curing conditions ”, by C. Unluer & A. Al-Tabbaa

MgO‐based binders

Carbonation curing of industrial solid waste‐based aerated concretes

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