Solubility and speciation of iron in cementitious systems

Fabio E Furcas,Barbara Lothenbach,O Burkan Isgor,Shishir Mundra,Zhidong Zhang,Ueli M Angst

doi:10.1016/j.cemconres.2021.106620

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.

Highlights

Steel corrosion is the most common cause of premature deterioration of reinforced concrete structures
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
Moti vated by these causes for corrosion, the modelling of chloride ingress and concrete carbonation in concrete has been a subject of research for a long time as evidenced by a range of ever-evolving transport models for quantifying the space-time evolution of species that initiate corrosion of reinforcement [15,16,17,18]

Summary

Introduction

Steel corrosion is the most common cause of premature deterioration of reinforced concrete structures. If present at sufficiently high quantities at the steelconcrete interface, can lead to the breakdown of the passive film that typically forms on steel surfaces in the alkaline environment of concrete [10,11,12]. Another possible cause for steel corrosion in concrete is carbonation of the cementitious phases and the associated loss in pH buffering capacity of the matrix surrounding the steel [13,14]. The transport and precipitation of iron species in the cementi tious matrix surrounding the steel are important steps that need to be considered in predicting corrosion-related damage of concrete struc tures, such as cracking and spalling [3,4,5,7,8,18,23,24,25,26]

Objectives

Methods

Conclusion