EFC Working Party 11: Corrosion of Steel in Concrete

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Task Group ‘Steel corrosion in alkali-activated materials’

The aims of EFC Working Party 11 ‘Corrosion of steel in concrete’ include fostering international cooperation, transfer of knowledge, and education. A current development in the field of cement and concrete is the development, characterisation, and optimisation of sustainable binder materials, due to the urgent need to reduce the CO₂ emissions caused by cement production and use. One of the most promising candidate materials for a mid- or long-term solution of the problem are so-called alkali-activated materials (AAMs), a class of cements that are produced by blending reactive aluminosilicates with alkaline solutions or salts of alkali metals. Consequently, there has been extensive research into these materials in the last decades.
Previous research has focused on the properties of the AAMs, and mortars and concretes produced from them, while the behaviour of reinforcing steel in AAMs has received less attention. Nevertheless, a significant number of papers on the topic has accumulated over the years. However, due to differences between conventional cements and AAMs, and the lack of experience with these new materials, the experimental approaches taken were not always appropriate and the interpretation and classification of the obtained data was constrained by considerable knowledge gaps. In parallel, research into the corrosion of reinforcing steel in conventional cementitious materials has progressed significantly, and its focus has shifted from the bulk material to microstructural characteristics of the steel–concrete interface, with possible implications also for studies of steel corrosion in AAMs.
These developments prompted the establishment of Task Group ‘Steel corrosion in alkali-activated materials’ with active members from several countries in Europe and the United States. The aim of the Task Group was do collate and synthesise the current knowledge about steel protection and corrosion in AAMs, particularly with a view on peculiarities of electrochemical methods commonly used to study steel behaviour in cementitious materials, to aid future studies on the topic. In the resulting report, the Task Group summarises relevant differences between conventional cementitious materials and AAMs and their consequences for analytical techniques such as open circuit potential, linear polarisation, and potentiostatic polarisation measurements. Results of the analysis with important implications include that commonly used values for parameters for the calculation of corrosion current densities of steel differ between conventional cementitious materials and AAMs, and that high sulfide concentrations in blast furnace slag‐based AAMs lead to results which might be incorrectly interpreted as indicating active corrosion of steel reinforcement, if conventional standards and recommendations are applied. Studies of the steel–concrete interface in AAMs are scarce and, thus, should be a priority for research in academia and industry.

The report of the Task Group has been published recently and can be freely accessed here: https://doi.org/10.1002/maco.202313743

Photograph of the Sheffield meeting (2018) of EFC WP11-Task Group ‘Steel corrosion in alkali-activated materials’

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