Table of Contents
Journal of Geochemistry
Volume 2014 (2014), Article ID 145425, 8 pages
http://dx.doi.org/10.1155/2014/145425
Research Article

Nature of C-(A)-S-H Phases Formed in the Reaction Bentonite/Portlandite

Department of Geology and Geochemistry, Faculty of Sciences, Autonomous University of Madrid, Campus Cantoblanco, 28049 Madrid, Spain

Received 30 September 2014; Accepted 3 December 2014; Published 18 December 2014

Academic Editor: Miguel A. Huerta-Diaz

Copyright © 2014 Raúl Fernández et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Reactions between bentonite/montmorillonite and portlandite have been studied in the context of the engineered barriers of a purpose built repository for the deep geological disposal of spent fuel and high-level radioactive wastes. Portlandite was selected as the representative material of cement leaching in the early alkaline stage expected in a repository when conventional Ordinary Portland Cement (OPC) is used. Eight different batch experiments were performed for a reaction time near to two months, including bentonite or montmorillonite at montmorillonite/portlandite molar ratios of 2 : 1 and 3 : 1 under hydrothermal conditions. Temperatures of reactions were maintained constant at either 60 or 120°C. Calcium silicates hydrates with limited substitution of Al for Si (C-(A)-S-H phases with Al/Si <0.3) were formed with different structures and compositions as a function of the reaction conditions. Orthorhombic 11 Å-tobermorite-type phase was detected in experiments at 120°C while a more disordered monoclinic tobermorite formed at 60°C. These results are useful for the interpretation of experimental data in more complex experiments using concrete or cement pastes and bentonite, where C-(A)-S-H phases of variable compositions can precipitate, in addition to the characteristic cement hydrates and other secondary minerals carbonates.