Characterisation of iron-rich cementitious materials

Iron is the fourth most abundant element in the Earth's crust, and cementitious materials are expected to contain iron-bearing phases, either in major or minor quantities. Iron-rich cement clinker is gaining attention because of its lower carbon footprint and higher sulfate resistance, while iron-rich resources are also increasingly being investigated as supplementary cementitious materials or as precursors for alkali-activated materials. However, iron-containing phases are among the least characterised in cementitious materials. This review paper discusses challenges in the characterisation of iron-containing phases for i) routinely used characterisation techniques, ii) specific characterisation techniques that excel at characterising iron-bearing phases, and proposes future areas of research to improve the accuracy and usability of these techniques. Micro-absorption, high X-ray and neutron scattering cross-section, fluorescence, and paramagnetism of iron can affect the application of X-ray diffraction, pair distribution function analysis, small-angle X-ray scattering, Raman spectroscopy, and nuclear magnetic resonance spectroscopy. X-ray absorption near-edge structure, extended X-ray absorption fine structure, 57Fe Mössbauer spectroscopy, and electron paramagnetic resonance spectroscopy are particularly suitable for characterising the iron oxidation states and local bonding environment in the iron-containing phases. UV–Visible spectroscopy, ion chromatography, and titration methods can be potentially used to quantify iron concentration and oxidation states in aqueous solution, but further research is required to apply them in the field of cementitious materials.