Purpose The purpose of this study is to use thermodynamic data to estimate the pressure exerted by the crystallization of iron oxyhydroxides following the equation proposed by Correns and Steinborn. Design/methodology/approach Standard free energy and molar volume data have been considered for goethite, lepidocrocite, magnetite and hematite, which are described in the literature as the most commonly found mineral phase rust constituents. Findings The studied mineral phases generate higher to lower crystallization pressure values in the following order: goethite > lepidocrocite > hematite > magnetite. The crystallization pressures calculated for these phases are in the 32-350 MPa range, which is higher than the tensile strength of concrete (of the order of 0.2-10 MPa) and thus leads to failure of the cover concrete. Originality/value The aim of this paper is to shed light on this issue by calculating the stresses generated by the crystallization of iron oxide from a supersaturated solution using thermodynamic data. A deliberately simplistic method was proposed, taking as reference the Correns–Steinborn model (Correns and Steinborn, 1939; Correns, 1949). The crystalline phases considered in this paper are those most commonly found in the literature as rust constituents, that is, goethite (α-FeOOH), lepidocrocite (γ-FeOOH), magnetite (Fe3O4) and hematite (α-Fe2O3). The FeO synthetic phase was also included as a reference.

Steel reinforcing bars are often coated with rusts formed during service in reinforced concrete (RC) structures. Rust layers growing on steel rebars induce expansive stresses and cause cracking on cover concrete. This study uses steel corrosion rate results measured on reinforced concrete buildings of more than 50 years of age located in marine environments and considers the pressure generated by the volume expansion of corrosion product layers to calculate the service life of the RC structures using a numerical simulation, estimating the time to corrosion cracking of the concrete cover. Akaganeite, goethite, lepidocrocite, hematite, magnetite and maghemite were identified by X-ray diffraction as crystalline phase constituents of the rust layers. RESUMEN: Predicción de la vida útil en servicio de edificios de 50 años expuestos a ambientes marinos.Los refuerzos corrugados de acero embebidos en hormigón, presentan con frecuencia una capa de herrumbre formada durante la vida en servicio de las estructuras de hormigón armado (EHA). Las capas de óxido, productos de corrosión, que crecen en los refuerzos de acero inducen tensiones expansivas y causan el agrietamiento del recubrimiento de hormigón. El presente estudio utiliza los resultados de la velocidad de corrosión del acero corrugado, medidos en edificios de más de 50 años, construidos con hormigón armado, ubicados en ambientes marinos. El estudio considera la presión generada por la expansión de volumen de las capas de productos de corrosión para calcular la vida útil en servicio de las EHA utilizando una simulación numérica, estimando el tiempo hasta la fisuración por corrosión del recubrimiento de hormigón. Akaganeita, goethita, lepidocrocita, hematita, magnetita y maghemita fueron identificadas por difracción de rayos X, como constituyentes de las fases cristalinas de las capas de óxido.

Electrochemical impedance spectroscopy was used to study the corrosion behavior of reinforcing steel embedded in alkaline activated fly ash mortar with chloride pollution. The porous nature of the rust layer was studied using a transmission line model and the parameters of the interfacial oxide/hydroxide film were determined by interpretation of the impedance data using a cylindrical pore. The rust layer generated on the steel surface was studied at the end of the experiment (two years) using scanning electron microscopy and X-ray diffraction.