Solubility and speciation of iron in cementitious systems
Fabio E. Furcas, Barbara Lothenbach, O. Burkan Isgor, Shishir Mundra, Zhidong Zhang, Ueli Angst
Abstract
Aqueous iron hydrolysis products and chloride complexes influence steel corrosion kinetics and dictate the amount and type of corrosion products formed. Here, we compile a thermodynamic database devoted to aqueous iron species and solid oxides as well as chloride complexes, aiming to describe their speciation and solubility within the prevailing chemical environment of interest for cementitious systems. We compare thermodynamic calculations to empirical data on the elemental composition of pore solutions from cementitious systems. It is found that dissolved iron concentrations in cement pore solutions can differ considerably from thermodynamic predictions. In particular, measured Fe(II) concentrations can exceed the thermodynamic limit by 2–5 orders of magnitude. Additionally, experimentally obtained iron solubility in the presence of chloride exceed thermodynamic predictions. We discuss that these differences may be explained by so far unknown iron complexes, stabilisation of intermediate phases such as chloride green rust, or due to (kinetic) hindrance of precipitation.