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Calcium aluminate blended cements incorporating engineered residues

Abstract : The pressure to decarbonize the cement industry in light of sustainability goals has been motivating the search for new types of supplementary cementitious materials (SCM) in the recent decades. Industrial residues, which otherwise end up in landfills or find low added-value applications, are of particular interest in near-zero-waste process schemes. This thesis explored the potential for valorization of pre-treated residues as SCM in calcium aluminate cement (CAC)-calcium sulfate hemihydrate (HH) system. These residues included non-ferrous metallurgy (NFM) slags, municipal solid waste incinerator (MSWI) bottom ashes, jarosite and paper-fabrication residues. Using isothermal calorimetry and mechanical strength test, a screening test was first established to compare their early-age and the long-term reactivity. The highly-amorphous NFM slags exhibited superior reactivity showing evidence of long-term (> 28 days) contribution to the mechanical strength of mortars at 30 wt% replacement level. However, the slags' slow hydration kinetics in the first days of hydration could be an issue for CAC systems, given that their applications greatly rely on their rapid-hardening property. Moreover, the amorphous nature of the NFM slags and the dominance of iron (Fe) in their composition, set them apart from traditional SCM's. As of this writing, there are only limited publications discussing the hydration mechanism of Fe in CAC-based binders. In order to overcome the slow kinetics of the slag hydration, the influence of three factors, including: (1) the proportion of sulfates by varying the CAC/HH ratio; (2) the addition of lime-rich paper residue at 5 wt% as activator; and (3) the incorporation of 30 wt% PC in ternary CAC-HH-PC systems, were investigated. For all these formulations, the early hydration reactions were characterized using isothermal calorimetry on paste samples. The dimensional stability and mechanical strength were followed using standard mortars up to 1 year curing period. Furthermore, a methodology to estimate the slag hydration degree using a non-destructive technique based on X-ray Computed Tomography (XCT) combined with volume analysis was developed in this study. Several techniques were used to follow the phase assemblage evolution, including: X-ray diffraction (XRD), thermogravimetric analysis (TGA), attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR). Lastly, transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM) and Mössbauer spectroscopy were also performed in order to gain a better understanding of the fate of Fe, the main component of the slag, during hydration.
Keywords : Cement Slag CAC SCM
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Submitted on : Tuesday, October 4, 2022 - 4:37:23 PM
Last modification on : Wednesday, October 5, 2022 - 4:00:12 AM

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  • HAL Id : tel-03797280, version 1

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Jennifer Astoveza. Calcium aluminate blended cements incorporating engineered residues. Mechanics of materials [physics.class-ph]. Université de Lorraine; Katholieke universiteit te Leuven (1970-..), 2022. English. ⟨NNT : 2022LORR0075⟩. ⟨tel-03797280⟩

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