Characteristic lengths of the carbonation front in naturally carbonated cement pastes: Implications for reactive transport models

Published on Aug 1, 2020in Cement and Concrete Research10.933
· DOI :10.1016/J.CEMCONRES.2020.106080
Fabien Georget4
Estimated H-index: 4
(EPFL: École Polytechnique Fédérale de Lausanne),
Wioletta Soja3
Estimated H-index: 3
(EPFL: École Polytechnique Fédérale de Lausanne),
Karen Scrivener87
Estimated H-index: 87
(EPFL: École Polytechnique Fédérale de Lausanne)
Sources
Abstract
Abstract Experimental evidence of a smooth carbonation front is often used to support the inclusion of kinetic reactions in reactive transport models. A new interpretation for a smooth carbonation front is proposed. We first show that the alkalis and sulfur can be used to map a natural carbonation front with energy dispersive spectroscopy. The resulting carbonation front is relatively sharp but tortuous. Most experimental methods takes an average over a volume which smooths the front. To illustrate this new interpretation, we also present a new carbonation model. Instead of using kinetic rates, we obtain a wider apparent carbonation front by considering a distribution of gas diffusion coefficients. The simulated profiles are similar to the experimental ones. This work does not prove that we should get rid of kinetic rates. However it demonstrates that similar macroscopic results can be obtained with very different assumptions. Therefore, these mechanisms must be quantified independently.
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Abstract Exposure of concrete to the atmosphere changes the microstructure of the cement paste. However, knowledge about the alteration of the porosity due to drying is typically not considered in deterioration processes of the hardened cement paste. The purpose of this article is to emphasize the importance of the porosity changes due to drying. 1 mm thick discs specimens made with four different pastes including three blended cements were exposed to CO2-free atmosphere at 70% relative humidity...
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Sensors demonstrate huge potential in civil engineering for monitoring the health condition and performance of concrete structures. Amongst various chemical deterioration mechanisms causing inadequate durability of concrete structures, carbonation is one of the most severe mechanisms. It occurs from the chemical reactions between intruded CO2 and calcium-bearing phases, hence is accompanied by the formation of calcium carbonate (CaCO3) and the decrease of the alkalinity of concrete pore solution...
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#1Fabien Georget (Princeton University)H-Index: 4
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Abstract During carbonation, the microstructure of a cement paste is strongly modified, which induces a dynamic feedback loop impacting the global advancement of the reaction. In this study, we investigate the effect of the microstructure model on simulations of accelerated carbonation of cement pastes. A variable-porosity reactive transport model with a new microstructure model is used. To match the chemical layers created by the carbonation front, we use a layered microstructure model. We demo...
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This study compares the phase assemblage and pore structure variation of Portland cement and blended cements, containing limestone and burnt oil shale, during carbonation. Hardened cement paste was exposed to natural carbonation (400 ppm of CO2) at a relative humidity of 70 % for one year. Samples were prepared and cured at 95 % RH for 28 days. Reference mixes were exposed to CO2-free atmosphere to decouple the effect of ongoing hydration and drying from that of carbonation. The phase assemblage...
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Calcareous fly ashes are high-potential reactive residues for blended cements, but their qualification and use in concrete are hindered by heterogeneity and variability. Current characterization often fails to identify the dominant, most reactive, amorphous fraction of the ashes. We developed an approach to characterize ashes using electron microscopy. EDS element composition of millions of points is plotted in a ternary frequency plot. A visual analysis reveals number and ranges of chemical com...
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#1Stefan van der Walt (Stellenbosch University)H-Index: 14
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scikit-image is an image processing library that implements algorithms and utilities for use in research, education and industry applications. It is released under the liberal Modified BSD open source license, provides a well-documented API in the Python programming language, and is developed by an active, international team of collaborators. In this paper we highlight the advantages of open source to achieve the goals of the scikit-image library, and we showcase several real-world image process...
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Abstract In this study, two methods were used to measure the carbonation depth of coconut fibre-reinforced mortars that were prepared from Portland cement (PC) and calcium sulfoaluminate cement (CSA cement), including traditional phenolphthalein reagent and thermogravimetric analysis (TGA). Accelerated carbonation was conducted at 4% CO2 concentration, temperature of 20°C and 65% relative humidity (RH) within 12 weeks. Complete carbonation was detected in the CSA cement-based mortar while PC-bas...
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Abstract The characterisation of cement paste microstructure is an important step towards understanding durability mechanisms in cementitious materials. Scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDS) is a widely used technique to analyse the microstructure at the micron-scale. However, it is challenging, notably because the characteristic size of many phases is found on a scale smaller than the EDS interaction volume. This work presents a new image analysis ...
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