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• Disentangle interphase inhibition mechanism of sodium borate for carbon steel. • Elucidation of the 3D structured stable double-layer Fe 2 O 3 /FeBO 3 passive oxide film. • Na 2 B 4 O 7 present a physicochemical adsorption process, which follows Freundlich isotherm. • Inhibition efficiency 86.3 % Na 2 B 4 O 7 ability to form a stable Fe–B–O interphase passive oxide film. • Mott-Schottky analysis revealed Na 2 B 4 O 7 produced less defective, and compact passive film. Sodium borate (Na 2 B 4 O 7) corrosion inhibition mechanism was studied on carbon steel rebars in 0.6 mol/L Cl– simulated concrete pore solution (SCPS) at different temperatures and concentrations. Electrochemical testing including cyclic potentiodynamic polarization (CPP), electrochemical impedance spectroscopy (EIS), and Mott–Schottky plots were utilized to understand the influence of inhibitor concentration and temperature on the thermodynamics of the adsorption and activation processes. It was found Na 2 B 4 O 7 imparts corrosion protection due to the formation of a 3D Fe–B–O stable interphase passive film, achieving an inhibition efficiency up to 86%. This can be attributed to the film having a lower donor current density and less vacancies, according to the Mott–Schottky tests. The formed interphase passive film was more stable and compact with less point defects compared to the blank due to Na 2 B 4 O 7 adsorption, this phenomenon was substantiated using the atomic packing factor, film thickness, and Mott–Schottky plots. It was revealed, using adsorption isotherms, that Na 2 B 4 O 7 interacted with the surface via physiochemical adsorption, creating a thinner/compact passive film composed of a rhombohedral calcite-type structure. SEM, XRD, and XPS were used to illustrate that Na 2 B 4 O 7 aides in the formation of a stable double-layered net structure Fe 2 O 3 /FeBO 3 passive oxide film. Finally, an interphase corrosion inhibition mechanism of Na 2 B 4 O 7 was proposed. [ABSTRACT FROM AUTHOR]

There is increasing interest in exploring the durability of structures manufactured with cements that are more environmentally friendly than traditional Portland. Accordingly, protection against chloride-induced corrosion of carbon steel reinforcement in mortars manufactured with environmentally friendly hybrid cements and alkali-activated materials (AAM) needs to be analyzed in-depth. Hybrid cements are innovative alternative binders with reduced amount of clinker in their formulation (20–30%). Their precursors are aluminosilicate wastes and they are very feasible in-construction implantation because they are not activated neither with liquid solutions of strong alkalinity nor external heating. In this research, AAM mortars were manufactured using slag from industrial by-products activated with sodium silicate. Hybrid mortars were manufactured either from fly ash or from slag, and activated with Na 2 SO 4. Portland cement (CEM IV) mortars were also included in this study as reference. Chlorides were made to penetrate into the four different mortars under study by diffusion. The porosity and chloride penetration were evaluated and related to the different materials. The electrochemical behavior of the steel reinforced mortar specimens was monitored by open circuit potential (OCP) and electrochemical impedance spectroscopy (EIS) measurements. The corrosion rate values obtained for steel embedded in AAM were similar to conventional CEM IV mortars, and the morphology of the attack is less localized. [ABSTRACT FROM AUTHOR]

• Mean stress pushing factor to fatigue damage. • Consideration of intrinsic and extrinsic mean stress. • Definition of three second-order fatigue effects. • Development of a 12-storey building as case study. • Proposition of a simple experimental setup. A fatigue process due to random loading that is progressively damaging a certain structural detail will vary in the presence of mean stresses. The variations are already considered in crack propagation laws and by applying equivalent 0-mean stress ranges from the Palmgren–Miner linear rule. Nevertheless, if the mean stress is intrinsic, instead of a direct consequence of the random loading, other second-order effects will have to be taken into account. Those effects are cycle quasi-ordering, histogram variations, and apparent mean tension, which are identified and defined in this study and, finally, developed in a case study for demonstrative purposes. [ABSTRACT FROM AUTHOR]