Iron speciation in blast furnace slag cements

• Published in: Cement and concrete research Vol. 140; p. 106287
• Main Authors: Mancini, A., Lothenbach, B., Geng, G., Grolimund, D., Sanchez, D.F., Fakra, S.C., Dähn, R., Wehrli, B., Wieland, E.
• Format: Journal Article
• Language: English
• Published: Elmsford Elsevier Ltd 01.02.2021; Elsevier BV
• Subjects: Blast furnace practice; Blast furnace slags; Corrosion; Hematite; Ilmenite; Iron; Iron sulfides; Laboratories; Magnetite; Oxidation; Pastes; Seawater; Slag; Slag cements; Speciation; Sulfides; Synchrotrons; Thermodynamic model; XAS; Slag; Iron; XAS; Corrosion; Thermodynamic model
• ISSN: 0008-8846; 1873-3948
• DOI: 10.1016/j.cemconres.2020.106287

Slag-containing pastes and concretes were analysed by element-specific synchrotron-based techniques to determine the speciation of iron on crushed materials through spatially resolved micro-spectroscopic studies. The investigated cement samples were hydrated either in the laboratory, or exposed to river or sea water. Metallic iron, along with minor proportions of iron sulphide and magnetite was detected in the laboratory sample. Iron sulphide, goethite, and siliceous hydrogarnet were discovered in the blended slag cements hydrated in contact with river water for up to 7 years. In contrast, no Fe(0) was observed in blended concretes exposed to sea water. Instead, iron sulphide, iron(II)-hydroxide and -oxide, hematite, magnetite, siliceous hydrogarnet, and goethite were detected as well as ilmenite (FeTiO3) in the aggregates. The strong acceleration of Fe oxidation in samples exposed to sea water and the long-term passivation observed in the other samples indicate comparable processes as those occurring on steel bars.