Zeta potential of cementitious materials through electroosmotic and electrophoretic experiments in decontamination: a critical analysis

Resumen del trabajo presentado en el XIII International Congress on the Chemistry of Cement, celebrado en Madrid (España), del 3 al 8 de julio de 2011The study of the properties of the interfaces between the solid phases and the pore water solution in hardened cementitious matrixes is a key point to understand a large number of properties and phenomena whose explanation only can be found at the nano-scale. The zeta-potential is the key parameter in the establishment of the electrokinetic effects and it can be defined as the average potential in an imaginary surface, which is considered to lie close to the solid surface, and within which the fluid is stationary during an electrokinetic process. When the solid remains stationary and the liquid moves in response to an applied electrical field this is called electro-osmosis, which is the case of the experiments using hardened cementitious materials through which the fluid moves. When the liquid does not move while the particles within it do, the phenomenon that takes place is the electrophoresis. In the case of contaminated construction materials, the development of an electroosmotic flux, with the corresponding dragging due to water transport, is a crucial mechanism to succeed in the treatment of decontamination. Therefore, it is of great interest trying to optimize the treatment by the addition of specific electrolytes enhancing the electrokinetic phenomena, and therefore, the great interest of determining the zeta potential in this field. Most of the data of zeta potential found in literature for construction materials are based in micro-electrophoresis measurements, which can be quite far of the real conditions of application of remediation treatments. In this paper, electrophoretic and electroosmotic experiments, with monolithic and powdered material respectively, have been carried out for mortar clean and contaminated with Cs, Sr, Co, Cd, Cu and Pb. The electrolytes tested have been distilled water, EDTA, oxalic acid, acetic acid and citric acid. The zeta potential values have been determined through the two different techniques and the differences have been critically analyzed