Carbon Steel Rebar Research Articles

The effect of simulated concrete pore solution composition and chlorides on the electronic properties of passive films on carbon steel rebar

Effects of simulated concrete pore solution composition, pH, and added chlorides on electronic properties of passive films on carbon steel rebar were investigated using Mott–Schottky (M–S) analysis. Passive films showed n-type semiconductive behavior with two discrete donor species and high donor densities. Deep donor densities increased with increasing passivation time. Less protective films resulted in lower space charge capacitances and lower flatband potentials. Sulfates had little influence on electronic properties. Chlorides caused a loss of linearity of M–S plots. This loss of linearity required higher chloride levels and longer exposure times to occur in higher pH solutions.

Numerical Investigation of the Role of Mill Scale Crevices on the Corrosion Initiation of Carbon Steel Reinforcement in Concrete

A numerical investigation was conducted to test the hypothesis that the composition of the pore solution in mill scale crevices on carbon steel rebar surfaces in concrete might be different from that of the bulk concrete pore solution, and this difference may create the necessary conditions for the premature breakdown of the passive film. The modeling was performed using a non-linear transient finite element algorithm, which involved the solution of coupled extended Nernst-Planck and Poisson's equations in a domain that represented typical mill scale crevices on carbon steel rebar. The numerical simulations showed that the chemistry of the pore solution, in particular pH and Cl−/OH−, within mill scale crevices provided more favorable conditions for depassivation than the bulk concrete pore solution. Local acidification and increase in Cl−/OH− within crevices were observed in all simulations, albeit to different degrees. Crevice geometry has been found to be the most important parameter affecting local acidification and the increase in Cl−/OH−. Simulations supported the hypothesis that the chemical composition of the pore solution within the crevices differs from that of the bulk solution through a process similar to the suggested mechanism of typical crevice corrosion.

Semiconductive Properties of Passive Films on Carbon Steel Rebar in Highly Alkaline Environments

In the highly alkaline environment of concrete, carbon steel rebar is protected against corrosion by a passive oxide/oxyhydroxide film. Understanding the characteristics of this passive film, and how it depassivates, is the key to mitigate problems associated with steel corrosion in concrete. Although a large number of electrochemical and analytical studies have been conducted on the passivity of steel in concrete, current mechanistic models do not explain all experimental observations about the chloride-induced depassivation process. One area that is not studied extensively is the electronic properties of passive films which show semi-conductive properties; a better understanding of these properties will provide additional information to improve the mechanistic models for chloride-induced depassivation of carbon steel in concrete. The present study uses Mott-Schottky (M-S) analysis along with other electrochemical techniques to study the electronic properties of passive films that form on carbon steel exposed to simulated concrete pore solutions. Both passivation and chloride-induced depassivation processes are investigated, and changes in electronic properties during these processes are monitored. The main parameters of the study include the concrete pore solution composition, pH, and chloride amount. Challenges of using M-S analysis to study the electronic properties of passive films will also be discussed.

Effect of tartrate on the electrochemical behaviour and semiconductive properties of passive film on steel in saturated calcium hydroxide

This paper presents results of the basic study on the inhibitive action of tartrate toward chloride‐induced corrosion on carbon steel rebar in alkaline environment. Modification of the electrochemical behaviour and semiconductive properties of passive film formed on steel surface in the presence of tartrate were characterised by a range of electrochemical techniques in saturated calcium hydroxide. In the presence of tartrate in saturated calcium hydroxide with addition of 0.14 M sodium chloride pitting corrosion initiation was postponed for 622 mV up to potentials of oxygen evolution reaction. The hypothesis on the competitive adsorption between the chloride ions and tartrate anion through the surface complex formation was applied on the studied system.

Electrochemical Behavior of Carbon and Thermo-Treated Steel Rebars Embedded in Concrete Exposed to Chlorides

One of the most used materials to reinforce concrete structures is the carbon steel rebar, however raw materials to produce carbon steel according to ASTM-A-615 standards are have become more expensive, so most of the production of this type of steel reinforcement is made from ferrous metal waste material; but, their physical and mechanical properties are barely sufficient for the requirements that the applications demand and the fact of using raw materials of a known stoichiometric composition to improve them can result in an increase of the cost production, so the implementation of heat treatment has been the most feasible alternative to achieve the required quality checks at reasonable prices. There is a great quantity of electrochemical data related to the mild steel rod, but the heat treatment produces a martensite outer layer, which may cause electrochemical differences. For this reason the main objective of this work was compare the electrochemical behavior between two different types of reinforcement, such as carbon steel and thermo-treated steel by QTB (Quenching Temperature Bar) process. The research was conducted in an accelerated exposure environment through immersion-drying cycles, using reinforced concrete specimens fabricated with water/cement ratios of 0.45 and 0.65.These specimens were monitored through electrochemical tests, such as the half-cell potential (HCP) and the linear polarization resistance (LPR). Finally the determination of the critical chloride concentration was performed with a potentiometric titration. A critical chloride concentration of 0.45% and 0.73% for total chlorides by weight of cement were obtained for thermo-treated steel and carbon steel, respectively; where the critical chloride concentration is parameter which defines the activation for a reinforced concrete structure. In this case the activation time was different, but the electrochemical results obtained in all the exposure period for both of the two reinforcing steels were similar. The results were used for develop two explications about of the activation time differences between the two reinforcing bars.

Corrosion Behavior of Stainless Steel Rebars Embedded in Concrete: an Electrochemical Impedance Spectroscopy Study

This work aims at studying the electrochemical behavior, by Electrochemical Impedance Spectroscopy (EIS), of austenitic (AISI 304 and AISI 316) and duplex (SAF 2205 and SAF 2304) stainless steels, when embedded in concrete specimens. Concrete specimens were exposed to chloride containing solutions simulating the aggressive conditions found in sweater environments. Samples were fully immersed and submitted to periodic immersion/emersion cycles. EIS and open circuit potential (OCP) were monitored in a monthly basis. Samples containing carbon steel (C-steel) rebars were also prepared for comparison of the corrosion rates between the different materials.The results showed that the austenitic and duplex SAF 2205 stainless steels were passive for all the testing period, due to the formation of protective oxide layer, with the AISI 316 presenting the higher corrosion resistance value. The EIS results suggest an increase of more than one order of magnitude in the corrosion resistance of the duplex steels and AISI 316 comparatively to C-steel rebars.

Comparación entre el comportamiento mecánico a tracción, fractura y fatiga de armaduras de refuerzo fabricadas con distintos tipos de acero

The use of austenitic stainless steels as rebar is an option increasingly used in reinforced concrete structures exposed to aggressive environments and especially those that have to work in marine environments. The same is true for duplex stainless steel rebars, although nowadays they have a lower use, mainly due to the fact that their inclusion in the reinforced concrete standards was delayed 10 years compared to austenitic stainless steel ones, and consequently their in-service behavior is not as well known. A study of the mechanical properties, including fracture toughness, fatigue behaviour and corrosion resistance in saline alkaline environments of austenitic (AISI 304LN and 316LN) and duplex (D2205) stainless steel reinforcing bars was performed in this work. Bars made on a high ductility carbon steel (B500SD) that are normally used to reinforce concrete were also characterized and used as a comparison. Stainless steel reinforcing bars show mechanical properties at least similar but usually higher than one of the best carbon steel re-bars (B500SD), along with a significantly higher ductility and, of course, much better corrosion behaviour in saline alkaline environments.

Materials and Corrosion 9/2013

Materials and CorrosionVolume 64, Issue 9 Cover PictureFree Access Materials and Corrosion 9/2013 First published: 20 September 2013 https://doi.org/10.1002/maco.201370091AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Abstract Cover: The difference in corrosion propagation behavior of 316LN stainless steel and carbon steel concrete reinforcing bar is highlighted on the cover. The top images of 316LN stainless steel rebar (left) and polished corrosion coupon (right) show areas of deep, localized corrosion while the bottom images of carbon steel rebar (left) and polished corrosion coupon (right) show widespread, shallow corrosion damage. The difference in how corrosion spreads during electrochemical testing on arrays of 100 microelectrodes of both 316LN stainless steel and carbon steel is shown graphically. The grids represents a microelectrode array with red shading indicating stable anodic dissolution. The middle two rows were preferentially initiated and the 316LN array showed no spreading to adjacent electrodes (top) while corrosion on the carbon steel array rapidly spread to adjacent electrodes (bottom). The rebar composition and manner which corrosion propagates will directly impact the lifetime of the concrete structure. More detailed information can be found in: M. F. Hurley, J. R. Scully, Lateral and radial corrosion propagation behavior of 9−21% Cr and 18% Cr + 2.8% Mo stainless steel reinforcing materials in simulated concrete environments, Materials and Corrosion 2013, 64, 752. Volume64, Issue9September 2013 RelatedInformation

Nano-scale study of passive films and chloride-induced depassivation of carbon steel rebar in simulated concrete pore solutions using FIB/TEM

Analytical TEM techniques were used to characterize passive film on carbon steel and how it breaks down with chloride addition. Before chloride addition, the thicknesses of the oxide films on rebars were found to be uniform between 5 and 13nm. The films consisted mainly of iron oxides that included nano-crystalites of FeOOH with an epitaxial relationship to the metal surface. Elements from the passivating solutions were located in regions of the oxide closest to the free surface. With the addition of chloride at concentrations below depassivation thresholds, there was evidence for change in the oxide closest to the free surface, but generally the oxides were similar to those grown before chloride addition. After exposure to chloride concentrations above depassivation thresholds, the oxide films were no longer uniform, with parts of the surface bare, and the average oxide thickness reduced. Pitting and enhanced corrosion were seen to accompany cementite lamella.

CORROSION INHIBITORS FOR CONCRETE CORROSION - AN OVERVIEW

Reinforced concrete is widely used for building materials and plays a significant role in economic development. However, the premature degradation of reinforced concrete structures due to the reinforcing steel corrosion has become a serious problem in modern society, which results in a huge economic loss. Under normal conditions, reinforcing steel in concrete can be protected from corrosion by forming a compact passive film on its surface in concrete pore solution with high alkalinity (pH 12.5-13.5). However, the passive film can be locally damaged and the localized corrosion of reinforcing steel takes place when pH and/or the chloride concentration at the steel/concrete interface reach the critical values for corrosion. Corrosion behavior of metals and alloys in concrete solution has been investigated in presence and absence of inorganic and organic inhibitors. Usually carbon steel and steel rebars have been used. Sometimes galvanized steel and SS316L have been used. Organic inhibitors, inorganic inhibitors, and natural products have been used as inhibitors along with concrete admixture. Corrosion resistance of metals has been evaluated by weight loss method, electrochemical studies such as polarization study and AC impedance spectra. Galvanostatic pulse technique has also been employed. The protective film formed on the metal surface have been analyzed by SEM, FTIR spectroscopy, XPS, AFM and EDAX. The protective film consists of metal-inhibitor complex, calcium carbonate and calcium hydroxide. Experiments have been carried out at room temperature. Corrosion inhibitors fill up the pores and prevent the penetration chloride ion towards the metal surface. Passive films formed on the metal surface also increase the life time of concrete rebars.

Bond characteristics of carbon and stainless steel flat rebars with an alternate rib pattern

The good performance of reinforced concrete depends on the appropriate transfer of forces between reinforcing rebars and concrete, which relies on the bond interaction between the two materials. At an uncracked section, both materials work together by means of the bond forces; however, if the tensile strength of the concrete is reached at a certain part of the structure, a crack will appear and the steel will be the only active element at the cracked section. At increasing loads, the crack will continue opening and large crack openings may lead to a failure of the rebar and to the collapse of the whole structure. A new idea to positively influence the cracking behaviour has emerged, which is based on the combination of smooth and rib zones within the same reinforcing rebar. Furthermore, use of stainless steel flat reinforcement has been considered as an option to optimize the reinforcing of shallow slabs. This paper presents bond tests performed on carbon and stainless steel flat reinforcements embedded in concrete and with different alternate rib configurations. Test results are presented in terms of bond strength and force transfer stiffness, as well as in terms of bond stress–slip relationship. Results show no differences between the bond capacity of carbon and stainless steel rebars if other parameters are kept constant. The use of an alternate surface configuration combining smooth and ribbed zones within the bond length, does affect the bond capacity of the rebar, and the position of the smooth zone within the bond length plays an important role.

Comparative Cathodic Behavior of ~9% Cr and Plain Steel Reinforcement in Concrete

The extent of the oxygen reduction reaction in concrete was evaluated for ~9% Cr rebar approaching the ASTM A1035 specification and compared to that of conventional carbon steel rebar, at ages of up to ~1 year. Cathodic strength was measured by the cathodic current density developed at −0.35 V vs. copper/copper sulfate (Cu/CuSO4 [CSE]) and −0.40 VCSE in cyclic cathodic potentiodynamic polarization tests, both in the as-received condition with mill scale and with scale removed by glass bead surface blasting. In both conditions the ~9% Cr alloy was a substantially weaker cathode, by a factor of several fold, than carbon steel. Within each material, the surface-blasted condition yielded also much lower cathodic current density than the as-received condition. For a small anode-large cathode system with a given anode polarization function, and no important oxygen reduction concentration polarization, the corrosion current was projected to be significantly lower if the cathodic region were ~9% Cr instead of plain steel rebar with comparable surface condition. There was strong correlation between the charge storage capability of the interface and the extent of cathodic reaction of oxygen. The result cannot be ascribed solely to differences in effective surface area between the different materials and conditions.

Impedance based method for non-contact determination of the corrosion rate in buried metallic structures

ABSTRACT The electrochemical impedance spectroscopy has been employed in the present investigation to assess the polarisation resistance of carbon steel rebars in different electrolytes. The measurements have been performed using the classical 3-electrode arrangement, where the element under test is the working electrode of the potentiostat, and a new 4-electrode arrangement where the element under test is floating from the electrical point of view (e.g. contact-less technique). The polarisation resistance values obtained using the contact-less technique are very close to those obtained using the traditional 3-electrode arrangement. The measurements, performed in a wide range of electrolyte resistivity values (including mortar) have thus demonstrated the applicability of this new technique for on-site corrosion rate assessment.

Corrosion behaviour of a new low-nickel stainless steel embedded in activated fly ash mortars

The present paper studies the corrosion behaviour of alkali-activated fly ash (AAFA) mortars manufactured using two alkaline solutions, with and without chloride additions (0.4% and 2%) in an environment of constant 95% relative humidity. Measurements were performed at early age curing up to 180 days of experimentation. A new, lower-cost type of austenitic stainless steel (SS) with a low nickel content was studied. Conventional austenitic AISI 304 SS and carbon steel rebar were also tested for comparative purposes. The evolution with time of corrosion potential, polarization resistance and electrochemical impedance spectroscopy were studied.

Impedance based method for non-contact determination of the corrosion rate in buried metallic structures

ABSTRACT The electrochemical impedance spectroscopy has been employed in the present investigation to assess the polarisation resistance of carbon steel rebars in different electrolytes. The measurements have been performed using the classical 3-electrode arrangement, where the element under test is the working electrode of the potentiostat, and a new 4-electrode arrangement where the element under test is floating from the electrical point of view (e.g. contact-less technique). The polarisation resistance values obtained using the contact-less technique are very close to those obtained using the traditional 3-electrode arrangement. The measurements, performed in a wide range of electrolyte resistivity values (including mortar) have thus demonstrated the applicability of this new technique for on-site corrosion rate assessment.

Microscopic investigation of mill scale and its proposed effect on the variability of chloride-induced depassivation of carbon steel rebar

Electrochemical experiments have shown that mill scale on carbon steel rebar affects corrosion initiation and variability associated with chloride-induced depassivation thresholds. In this study, scanning electron microscopy and focused ion beam microscopy were used to investigate the properties of mill scale and its effect on chloride thresholds of the underlying steel. The variability found in the literature for chloride thresholds is suggested to result, in part, from the variability in the physical and chemical properties of mill scale. A crevice corrosion mechanism is proposed to explain why as-received rebar is more susceptible to depassivation than rebar without mill scale.

Evaluation of the corrosion inhibition of salts of organic acids in alkaline solutions and chloride contaminated concrete

AbstractThis paper summarizes the results of testing on salts of organic acids for evaluating their use as inhibitors of rebar corrosion in chloride‐contaminated concrete. Initially a screening based on electrochemical tests in alkalinized calcium hydroxide solutions was performed on a number of carboxylic acid salts with different number of carbon atoms in the chain and carboxylic groups, also covering substances with hydroxyl and amine group substituents. The screening was completed by testing on carbon steel rebars in concretes with chlorides and substances added at 1:1 molar ratio, focused on sodium lactate, sodium oxalate and sodium borate for comparison. The monitoring of free corrosion potential and linear polarization resistance of steel bars have confirmed significant inhibition only for lactate. Corrosion was only restricted to occluded zones where the access of substance was limited by disadvantageous geometry, producing shallow attacks.Results of further tests in saturated calcium hydroxide solution are reported in order to assess the inhibition ability of lactate as a function of its content, chloride content and pH.

A study of organic substances as inhibitors for chloride-induced corrosion in concrete

Chloride-induced corrosion of carbon steel reinforcement is the most important cause of premature failure on reinforced concrete structures. Among available methods, corrosion inhibitors offer a simple and cost effective prevention technique, primarily to prevent and stop chloride-induced corrosion. Nevertheless, performance of commercial inhibitors is only partially satisfactory. This paper deals with a basic study on the inhibitive action of organic substances toward chloride-induced corrosion on carbon steel rebar in alkaline environment. The effect of aminic and carboxylic groups was investigated through electrochemical potentiodynamic polarisation tests in simulating concrete pore solution in the presence of chlorides, to ascertain inhibitor effectiveness to increase pitting potential. Results are discussed taking into account the most likely mechanism of inhibition, in relation to the functional group of tested organic compounds.

Electrochemical and in-situ SERS Study of Passive Film Characteristics and Corrosion Performance of 9%Cr Microcomposite Steel in Highly Alkaline Environments

Abstract The passive films formed on the 9%Cr, 0.1%C, microcomposite steels (ASTM A1035) in highly alkaline environments, such as concrete pore solutions, were studied. In-situ surface-enhanced Raman spectroscopy (SERS) was conducted during cyclic potentiodynamic polarization experiments to characterize the formation and breakdown mechanisms of the passive films formed. A solution of 0.55 M KOH + 0.16 M NaOH, with and without chlorides (0 % and 3.5 % NaCl), was used for the SERS experiments. In addition, the corrosion performance of microcomposite steels as a function of pH (9–13) and ionic strength of the solution (from 10-5 to 10-1 M) was evaluated via polarization resistance (Rp) experiments, and compared to the performance of regular carbon steel. Results show that the passive film formed on the microcomposite steel seems to be characterized mainly by the presence of Cr(OH)3 and minor amounts of Fe species; more specifically Fe3O4 and a Fe(III) phase. The film is considerably more protective than that formed on conventional carbon steel under the same test conditions. Microcomposite steel has not shown a reduction of polarization resistance as a function of pH drop when the ionic strength of the medium was kept constant, in a stark contrast to the behavior verified for the regular carbon steel rebar.

Behavior of Corrosion of Steel Embedded in Ternary Concretes

The electrochemical characterization of the behavior of reinforced concrete using ternary mixtures was carried out with the objective of decreasing the degradation rate of reinforced concrete structures caused by corrosion. The materials used were: Fly ash, micro-silica, and ground granulated blast furnace. During the experimental process, 11 ternary concrete mixtures where up to 20% wt. of Portland cement was substituted with two of the previously mentioned additives in different percentages in each mixture. Then two low carbon steel rebars that functioned as electrodes were embedded into the mixtures. Afterwards, a 3.5% wt. NaCl solution was placed on the sample for 13 months. Through the use of electrochemical techniques, it was observed that the mixture of 5% flying ash + 15% micro-silica + 80% Portland cement presented the best protection of the reinforcing bar, decreasing the corrosion rate with respect to a control mixture of 100% Portland cement.