Measurement and modeling of the surface potential evolution of hydrated cement pastes as a function of degradation |
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Authors: | Pointeau Ingmar Reiller Pascal Macé Nathalie Landesman Catherine Coreau Nathalie |
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Affiliation: | CE Saclay, DEN/DANS/DPC/SECR, Laboratoire de Mesures et Modélisation de la Migration des Radionucléides, Bat. 450, BP 11, 91191 Gif-sur-Yvette Cedex, France. ingmar.pointeau@cea.fr |
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Abstract: | Hydrated cement pastes (HCP) have a high affinity with a lot of (radio)toxic products and can be used as waste confining materials. In cementitious media, elements are removed from solution via (co)precipitation reactions or via sorption/diffusion mechanisms as surface complexation equilibria. In this study, to improve the knowledge of the surface charge evolution vs the degradation of the HCP particles, two cements have been studied: CEM-I (ordinary Portland cement, OPC) and CEM-V (blast furnace slag and fly ash added to OPC). Zeta potential measurements showed that two isoelectric points exist vs HCP leaching, i.e., pH. Zeta potential increases from -17 to +20 mV for pH 13.3 to pH 12.65 (fresh HCP states) and decreases from 20 to -8 mV for pH 12.65 to 11 (degraded HCP states). The use of a simple surface complexation model of C-S-H, limited in comparison with the structural modeling of C-S-H in literature, allows a good prediction of the surface potential evolution of both HCP. Using this operational modeling, the surface charge is controlled by the deprotonation of surface sites (>SO(-)) and by the sorption of calcium (>SOCa(+)), which brings in addition a positive charge. The calcium concentration is controlled by portlandite or calcium silicate hydrate (C-S-H) solubilities. |
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