Enhancement mechanisms of Cr and RE on the corrosion resistance of HRB400 rebar in chloride-containing concrete pore solution

It is well known, that reinforcement steel in concrete is normally protected against corrosion due to the high pH-value of the pore solution of the concrete. This alkalinity leads to a passive layer on the steel surface, which prevents further corrosion. The passive layer can be destroyed by chloride ions diffusing into the concrete. The concentration of chloride in the concrete which leads to a destruction of the passive layer and therefore to corrosion of the steel is defined as the critical chloride content. Investigations in artificial concrete pore solutions show that the critical chloride content of black steel is strongly dependent on the pH-value of the solution: the higher the concentration of the OH - -ions the higher the critical chloride content. For steel fibres earlier investigations have shown, that steel fibres do not corrode in concrete even at high chloride contents. Therefore it could be assumed, that the critical corrosion-inducing chloride content of steel fibres in concrete is distinctly higher than of conventional reinforcing steel. To verify this assumption the corrosion-inducing chloride content of steel fibres is investigated in artificial chloride-containing concrete pore solutions at different pH-values. 5 different types of steel fibres, 1 lashing wire and as reference 1 reinforcing steel are investigated at 3 different pH-value ranges. The concentration of chloride within the pore solution is gradually increased in time steps of 12 h. The beginning of corrosion is determined by current as well as potential measurements. Furthermore additional investigations are carried out with intermediate products of the fibre production (steel wires with different diameters) to investigate if the critical chloride content of the wires is increasing gradually with decreasing diameter. The investigations show, that steel fibres in artificial chloride-containing pore solutions indicate an distinctly increased resistance against chloride-inducing corrosion compared with conventional reinforcing steel for high pH-values. With decreasing diameter of wires the critical chloride content increases gradually.

Study of the passivation of carbon steel in simulated concrete pore solution using scanning electrochemical microscope (SECM)

Key words：carbonization , chlorine salt ,potential , critical molar ratioAbstract：By chlorine salt and carbonization under the combined action of simulated concrete pore solution in determination of the natural potential of the reinforced method of the influence of basicity of chloride contaminated concrete critical NO2 -/Cl -molar ratio.Results show:The increase of pH value or NO2 -/Cl -molar ratio in concrete simulated pore solution can inhibit the corrosion of reinforcing steel bar;The NO2 -/Cl -molar ratio of molar ratio less than the critical NO2 -/Cl -mole ratio of the actual concrete is suppressed in the concrete simulated pore solution;The pore solution simulation has the concrete carbonization, corrosion inhibition required NO2 -/Cl -molar ratio is 3 times of ordinary concrete carbonation.

Metakaolin concrete is a kind of porous material, which contains a variety of chemical ions in the pores. Solutions in these pores are exposed to the atmosphere and exist evaporation and condensation processes, therefore, the pore solution volume of concrete changes all the time. When the ion concentration in the pore solution changes, it has an important impact on the strength development and durability of concrete. However, the real-time monitoring of the concentration of pore solution was difficult. To study the chemical evolution of pore solution in concrete, the variation of saturated vapor pressure on the surface of metakaolin concrete was studied based on the Cisternas-Lam rule. The evaporation rate of solvent in the pore solution of concrete under the corresponding saturated vapor pressure in this paper was studied by the Stefan diffusion method. The dynamic equilibrium process equation of ions in pore solution was then established based on the thermodynamic equilibrium equation. Based on the above model, the change process of the pore solution of metakaolin concrete was studied, and it was verified by the results of the literature.

The present work discusses the effect of five different microstructures, coarse, fine and very fine ferrite–pearlite, martensite and tempered martensite, made by furnace cooling, air cooling, forced air-cooling, water quenching and tempering, respectively, of a rebar steel on its corrosion performance in freely aerated with and without chloride-contaminated simulated concrete pore solution using the dynamic polarization and electrochemical impedance spectroscopy. The corrosion performance of the steels with five different microstructures relates to the polarization resistance, protective ability of rusts and the extent of the galvanic attack. The corrosion rate of the steels has been found to be comparable in the simulated concrete pore (SCP) solution. However, in chloride-containing SCP solution, corrosion rate has been found to increase in the following sequence: forced air-cooled–air-cooled–quenched–furnace-cooled–tempered steels.

The passive ranges of carbon steel rebar and 3Cr steel rebar in saturated Ca(OH) 2 ‐simulated concrete pore solution with pH 12.6 were determined by means of cyclic voltammetry and potentiodynamic polarization curves. Chronopotentiometry was used to obtain steady‐state conditions for the formation of passive films on rebar samples at different anodic potentials. Electrochemical impedance spectroscopy, Mott–Schottky and X‐ray photoelectron spectrometer curves were employed to compare the formed passive films at different potentials. Additionally, cyclic polarization curves were used to compare the corrosion resistances of formed passive films on the two rebars in saturated Ca(OH) 2 ‐simulated concrete pore solution with different concentration of Cl − . The results show that the passive ranges of the two rebars are all between −0.15 and +0.6 V, and more stable passive films can be formed on both rebars at the anodic potential of +0.3 V. In the absence of Cl − , the stability and corrosion resistance of the passive film formed on the 3Cr rebar are better than those of CS rebar. The passive film of 3Cr steel has the relatively better pitting corrosion resistance than carbon steel in saturated Ca(OH) 2 ‐simulated concrete pore solution that contains different concentration of Cl − . Copyright © 2016 John Wiley & Sons, Ltd.

As the main problem of the durability deterioration of concrete structures, the corrosion of steel bars is usually made by the method of electrified corrosion with a short cycle and low cost. However, there is a big difference between the actual corrosion depth and the theoretical corrosion depth after the reinforcement is electrified. In this paper, through the accelerated corrosion test of steel bars, the change law and influence factors of corrosion efficiency of steel bars in concrete simulated pore solution and NaCl solution are studied. The test results show that the corrosion efficiency of reinforcement in the NaCl solution is higher than that in the concrete simulated pore solution, and the corrosion efficiency in the NaCl solution changes in two stages with the corrosion degree of reinforcement. The corrosion efficiency of concrete in the simulated pore solution decreases with the increase of corrosion degree of reinforcement, which is more significant than that in the NaCl solution. Under the same conditions, the corrosion efficiency is higher in the chloride ion solution with high concentration, and the influence of chloride ion concentration change in the simulated pore solution of concrete on the corrosion efficiency is more significant. The corrosion efficiency of reinforcement under low current density is higher than that under high current density.

The influences of the rust layer on the passivation and corrosion of Q235b carbon steel in simulated concrete pore solution were studied. The differences between the inner and outer rust layer were characterized. Results show that the pre-rusted samples could still reach passive state at high pH condition free of chloride ions. However, the quality of the passive film formed on the pre-rusted steel were dramatically lower than that formed on the fine polished steel. The pitting corrosion resistance of the pre-rusted steel was significantly higher than that of the fine polished steel in the chloride-containing pore solution. The pitting corrosion potential would be further promoted after the elimination of the outer rust layer. The reaction between the hydrogen ions and the rust layer could inhibit the pitting initiation. Furthermore, the consumption of the corrosive agents induced by the rust layer could further retard the area expansion of the pits.

Bentonite is used as a buffer material in the final disposal sites of high-level radioactive waste. Its expansibility is affected by cement-based materials with high pH values; however, existing studies rarely use actual cement-based materials. This study applied the swelling rate of the swelling index test to evaluate the influence of actual concrete alkali concentrations and temperatures on the swelling properties of bentonites. The results showed that when bentonite was placed in the concrete pore solutions with high pH value at 23 and 80°C, the swelling capacity was obviously reduced, whereas the low-pH concrete solution did not reduce the swelling capacity of bentonite. The number of alkali metal ions in the low-pH concrete reacting with the bentonite was 0.8–1.8% of that in the highly alkaline concrete. The temperature rise increased the swelling rate of the bentonite. The required test period of the bentonite swelling index test was short. This method observed an obvious increase in the main swelling stage, which was favorable for judging the influence of concrete alkalinity on bentonite. Thus, the swelling rate calculated from the swelling index test was appropriate for evaluating the influence of actual concrete solutions and temperature on the swelling properties of bentonite.

Threshold chloride concentration for stainless steels activation in concrete pore solutions

The nanoscale passive film formation on steel reinforcing bars at different stages of their exposure in concrete pore solution is characterized by the application of atomic force microscopy, Raman spectroscopy, electrochemical impedance spectroscopy, electrochemical noise, and cyclic voltametry studies. Based on this, a new description of the sequence of reactions during the formation of passive film on steel reinforcing bars is suggested in this paper. The results generated during this investigation revealed that the surface of the steel reinforcing bars prior to their embedding in a concrete pore solution remain covered with a film of ferric hydroxide (Fe(OH)₃). The passive film on the reinforcing bars is formed by the dissolution of this oxide film followed by a series of chemical reactions. The nanotechnological investigations conducted in this paper indicated that a protective passive film on a reinforcing bar’s surface develops within 24 hours of its exposure to the concrete pore solution. Further exposure helps growth of the film over a period of up to 7 days. Beyond this period of exposure, no significant changes in either the structure or the protective property of the film are recorded. In solid concrete, however, the film formation and its growth is slow compared with the concrete pore solution, and a minimum period of 20 days is needed to form a complete protective film on the reinforcing bars embedded in concrete.

Effect of triethanolamine and sodium hexametaphosphate on formation, growth and breakdown of passive layer in concrete pore solution

The impact of sandblasting as a surface modification method on the corrosion behavior of steels in simulated concrete pore solution

Characterisation of coating on rebar surface using Hot-dip Zn and Zn-4.9Al-0.1 misch metal bath

Characterization of atomic structure of oxide films on carbon steel in simulated concrete pore solutions using EELS