Passivation Behavior Of Steel Research Articles

Enhanced passivity of reinforcing steel in cementitious materials with thermally-activated red mud

Red mud (RM) is a solid waste from aluminium industry that can be used as an emerging supplementary cementitious material, and it has beneficial effects on the corrosion resistance of reinforcing steel in concrete. However, the low reactivity of RM reduces the comprehensive performance of cementitious materials, thereby limiting its widespread application in concrete. In this study, RM was thermally activated and the phase transformation behavior of the thermally-activated RM (TA-RM) was studied. Additionally, the passivation behavior of steel in extract solutions and mortars containing RM with and without thermal activation was investigated using electrochemical methods, surface characterization techniques and compositional analysis. The results showed that the reactivity of RM was effectively improved by the thermal activation treatment due to the phase transformation, and the enhanced steel passivity was observed in both extract solution and mortar with TA-RM. Compared to steel exposed to extract solutions, the mortar containing TA-RM could provide an additional protection for the embedded steel by forming a compact steel-mortar interface, further improving its passivation ability.

Passivation of Steel Reinforcement in Low Carbon Concrete

Both the high CO2 emissions associated with cement production and the increasing demand for concrete call for the use of binder types that can be produced in a more climate-friendly way than that of ordinary Portland cement. To ensure that these binders can also be used in reinforced concrete structures, their influence on the corrosion behavior of embedded steel reinforcement must be investigated. In the study presented here, the passivation behavior of steel in mortars made from various new types of binders is investigated. In addition to alkali-activated materials with high and low calcium contents, a calcium sulfoaluminate cement and a binder produced from calcium silicate hydrate (C-S-H) phases, synthesized in an autoclave, were investigated. While the steel clearly passivated in the alkali-activated slag and the C-S-H binder, the calcium sulfoaluminate cement showed the lowest open circuit potentials and polarization resistances, indicating a less effective level of passivation. The metakaolin geopolymer with a potassium-based activator showed an onset of passivation that was dependent on the environment of the specimens at an early age, whereas the alkali-activated fly ash with a sodium-based activator showed a delay in passivation that was not influenced by the environment of the specimens at an early age.

Comparative investigation on the influence of metakaolin, metaillite and steel slag as SCMs in mortar on the corrosion behavior of embedded steel

Abstract With the aim of saving CO2 in cement production, various approaches are currently being pursued in the development of new materials. One possibility is to reduce the ratio of clinker to cement by using supplementary cementitious materials (SCMs). Some SCMs like fly ash or granulated blast furnace slag have been used successfully in cement for a long time and their use is covered by standards. Since the availability of these materials cannot be ensured in the long term, alternative additives are also being tested. The results presented here were obtained as part of a joint research project that was carried out in cooperation with the Bauhaus University Weimar. In this study, three different SCMs are investigated with regard to their effect on the corrosion of steel embedded in mortars: A metakaolin, a metaillite, and a modified steel mill slag were each tested at a proportion of 30 wt.% in a CEM I reference cement. In the two-stage tests, the passivation behavior of steel in mortars was first investigated in electrochemical tests. Based on this, tests were carried out in leached solutions of the different binders with different Cl–/OH– ratios. The results show that all the blended types of cement investigated provide passivation of the steel in mortar. The use of the calcined clays metakaolin or metaillite resulted in higher polarization resistances and lower passive current densities as well as increased electrical resistivities, especially for metakaolin. The steel in mortar with the steel mill slag showed comparable electrochemical behavior to the OPC mortar. The tests in leached solutions slightly indicate a higher corrosion-inducing Cl–/OH– ratio when using metakaolin or steel mill slag.

Potentiodynamic polarization studies of the pitting corrosion resistance and passivation behavior of P4 low carbon mold steel in chloride and acid chloride solution

Potentiodynamic polarization studies and open circuit potential measurement of P4 low carbon mold steel (P4LC) was performed to assess its pitting corrosion resistance in specific concentrations of chloride and acid chloride solutions. Results showed the corrosion rates of P4LC were generally higher in the acid chloride media. P4LC displayed significant pitting resistance, independent of chloride concentration in the chloride media. The chloride attack was determined to be the consequence of film breaking and penetration mechanism. Delayed passivation coupled with metastable pitting activity occurred at the anodic region of the polarization plot in the acid chloride solution and beyond a certain chloride concentration in the acid chloride solution, passivation behavior of the steel was completely absent due to the combined electrochemical action of and Cl− ions. O2 reduction was the dominant cathodic in the chloride solution while H2 evolution was the dominant reaction in the acid chloride media. Data from open circuit potential analysis shows the oxide film formed on P4LC in the chloride solution was sustainable from the positive shift in corrosion potential while in the acid chloride solution the corrosion potential were more electronegative. The morphology of P4LC showed the presence of deep elliptical corrosion pits at low chloride concentration while at higher chloride concentration fewer but larger pits in the form of vertical grain attack were visible. The morphology of P4LC from the acid chloride solution showed the presence of large number of deep elliptical corrosion pits coupled with a more deteriorated surface.

Passivation Behavior of Carbon Steel Alloy in the Presence of EDTA, Ni(II)EDTA, and LiOH at 473 K

Abstract A comparison has been made between the passivation behavior of steel in pH 10 (at 298 K) ethylenediaminetetraacetic acid (EDTA), Ni(II)EDTA, and LiOH dosed deoxygenated (<50 mg/kg dissolve...