Comparative kinetics study on carbonation of ettringite and meta-ettringite based materials

https://doi.org/10.1016/j.cemconres.2020.106209Get rights and content

Abstract

The use of ettringite-based materials for thermochemical heat energy storage has attracted researchers' attention in recent years since ettringite has advantages like low material cost and high energy storage density (~500 kWh/m3). However, carbonation, which modifies its structure and reduces the capacity of energy storage, is an important hindrance to real applications. To address this issue, the present study focuses on the carbonation kinetics of three ettringite-based and corresponding meta-ettringite-based materials (dehydrated samples) exposed to different relative humidity (RH) and CO2 concentrations. A mixture of 80 wt% pre-blended Calcium Aluminate Cement/20 wt% OPC (C80P20) proved to be the most resistant against CO2. The hydrated and dehydrated C80P20 grains carbonated slowly at 50% RH and 1 vol% CO2, consuming little ettringite after 28 days. At 90% RH, carbonation was accelerated such that all ettringite and meta-ettringite materials were depleted at 11 days with vaterite and aragonite as the main calcium carbonates. The produced CaSO4 hydrates were found as hemihydrate at 70% RH and gypsum at 90% RH. Finally, the thermal energy storage capacity (TESC) of the material was systematically quantified as essentially decreasing with the carbonation degree of ettringite-based materials.

Section snippets

Cement chemist notation

AAlumina (Al2O3)
CLime (CaO)
C¯Carbon dioxide (CO2)
HWater (H2O)
MPericlase (MgO)
SSilica (SiO2)
S¯Sulphur trioxide (SO3)

Materials

High calcium aluminate cements containing additional calcium sulphate (p-CAC and BCSAF) were used to obtain pastes rich in ettringite. To produce pastes with different ettringite contents, some p-CAC was mixed with OPC (CEM I 52.5 N), improving mechanical properties and decreasing the risk of self-breakage due to significant shrinkage. The BCSAF was light brown cement with high ye'elimite content. Chemical compositions and mineralogical phases of the three cements were analysed by X-ray

Characterisation of reference materials before carbonation

The physical characteristics of the hardened mixtures are summarised in Table 4 using methods like theoretical CO2 binding capacity, water vapour isothermal absorption, MIP, and compressive strength. The grains of different mixtures were generally in the 1–2 mm and 2–4 mm ranges. For C80P20, the mean size was 1.04 mm for 1–2 mm, while it was 2.07 mm for 2–4 mm. Similarly, it was 0.98 mm and 2.50 mm for 1–2 mm and 2–4 mm of C60P40, respectively, 1.13 mm and 2.11 mm for BCSAF. The compressive

Discussion

This work studies the carbonation of cement-based materials rich in ettringite/meta-ettringite for potential thermal energy storage use. The evolution of ettringite and carbonate content is discussed, with a comparison of two other materials with high ettringite content. Although ettringite is a dominant phase in these materials, other hydrates like monosulfate, strätlingite, and calcium aluminate hydrates contribute against carbonation to protect ettringite. The influence of CO2 on the

Conclusion

This study significantly advances the understanding of natural and accelerated carbonation of ettringite and meta-ettringite-based material. The current results of carbonation experimentations typically conducted by TGA and XRD lead to the following conclusions.

  • 1.

    Relative humidity is the key controlling factor of carbonation, whatever the grain size (1 to 4 mm) of ettringite and meta-ettringite-based materials. Both the instantaneous rate of carbonation and the maximum degree of carbonation (up

CRediT authorship contribution statement

Author 1: Bao Chen

  • a)

    Conceived and designed the analysis

  • b)

    Collected the data

  • c)

    Contributed data or analysis tools

  • d)

    Performed the analysis

  • e)

    Wrote the paper

Author 2: Matthieu Horgnies

  • a)

    Conceived and designed the analysis

  • b)

    Contributed data or analysis tools

  • c)

    Performed the analysis

  • d)

    Wrote the paper

Author 3: Bruno Huet

  • a)

    Conceived and designed the analysis

  • b)

    Contributed data or analysis tools

  • c)

    Performed the analysis

  • d)

    Wrote the paper

Author 4: Vincent Morin

  • a)

    Conceived and designed the analysis

  • b)

    Contributed data or analysis tools

  • c)

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgement

The authors would like to thank LafargeHolcim Innovation Center and Association Nationale de la Recherche et de la Technologie (ANRT) of France for the funding of this research. The authors address the appreciation to Mouna Boumaaza, Isabelle Baco and the analytical support team from LafargeHolcim Innovation Center for their precious discussions and analysis support.

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