A literature review was conducted with the goal of identifying alternative low-cost corrosion resistant steel reinforcement materials. The most promising alternate reinforcing materials seen to date that are less expensive than 300 series stainless steels include low-nickel austenitic stainless steels, and a variety of ferritic or martensitic 12-15 weight percent chromium steels. Steels with 2.5-10 weight percent chromium may also be of interest because they offer a marginal gain in corrosion performance at a very low cost. Several steel types that should undergo further evaluation are 201LN, 216, S41003, S24100 and S24000, HSS2, S41425, S41426, and S42300.
Samples with two different binary blended concrete mixes were prepared, one containing cement replacement of 50% slag (referred here as SL mix) and the other containing cement replacement of 20% fly ash (termed here as FA mix). The water to cementitious ratio used to produce concrete specimens was 0.41. On the top surface of each specimen, various reservoir lengths that ranged from 2.5 cm to 17.5 cm were fitted, and these reservoirs were filled with a 10% NaCl solution. Electromigration was used to accelerate the transport of chlorides, with an applied potential of 9V at first, and subsequently reduced to 3V after about a week. For a period of about 1100 days, the corrosion related parameters such as concrete solution resistance, rebar potential, and corrosion current were monitored via the rebar potential measurements, linear polarization resistance (LPR) and electrochemical impedance spectroscopy (EIS) measurements, the latter used only to obtain the solution resistance. The corrosion current values determined through experimental observations were then converted to mass loss using Faraday’s law. The readings of corrosion current values (last 10 sets of readings) as well as the calculated mass loss values were found to be larger for the rebars embedded in specimens prepared with SL mix, followed by rebars embedded in specimens prepared with FA mix. Corrosion current and calculated mass loss values in general tended to increase with increasing solution reservoir lengths. No cracks or corrosion products that reached the surface of the concrete were observed on the specimens for the duration of the reported monitored propagation period. This study offers a framework for future studies on accelerated steel corrosion in concrete.
The inhibition of the oxygen reduction reaction (ORR) on copper was investigated after pretreatment with Co, Ce, and Mo ions at applied potential simulating galvanic coupling to AA2024-T3. Specifically, the effect of Ce(III), Co(II), and pretreatments on ORR was investigated in the mixed charge transfer, mass transport regime in pH 7-11 solutions using the Koutecky-Levich approach. Co reduces the ORR rate the most in more alkaline solutions (pH 9.5) while the Ce pretreatment works best in slightly less alkaline solutions (pH 7-8.2). Mo pretreatment was also most effective at pH 8.2 and was ineffective at pH 11. These results were consistent with chemical precipitation of and or . was rationalized to be formed by electrochemical reduction of on copper. This process was not operative at highly alkaline pH at applied potentials near the open circuit potential of AA2024-T3.
Corrosion inhibition of aluminum alloy (AA)2024-T3 (UNS A92024) in sodium chloride (NaCl) solutions after pretreatments in solutions containing Ce(III), Co(II), or Mo(VI) ions are reported...
Close packed coupled multi-electrodes arrays (MEA) simulating a planar electrode were used to measure the anodic current evolution as a function of position during initiation and propagation of crevice corrosion of AISI 316 stainless steel (UNS S31600) and Ni-Cr-Mo alloy 625 (UNS N06625). Scaling laws derived from polarization data guided the implementation of rescaled crevices providing spatial resolution. Crevice corrosion of AISI 316 stainless steel in 0.6 M NaCl at 50{degree sign}C was found to readily initiate close to the crevice mouth (i.e., xcrit ≈ 0) at modest applied potentials (e.g., 0 VSCE) and to spread inwards and outside the crevice with time. In the case of alloy 625, crevice corrosion initiates further inside the crevice (i.e., xcrit is large) and requires higher applied potential (e.g., 0.05 VSCE). The local crevice current density increased dramatically over a short period to reach a limiting value in both cases.
Surface resistivity profiles (using a wenner probe) as a function of elevation are being measured on young and mature marine reinforced concrete substructures at and above mean water line on bridges at coastal locations in Florida. The surface resistivity values measured are correlated with chloride diffusion coefficients measured from the same structures. Additionally the wet resistivity values from cored specimens are also correlated to the chloride diffusivity. Previous lab work suggests that a good correlation exists on saturated concrete between these two parameters. The objective of this study is to assess whether a similar correlation can be obtained from field surface resistivity readings, such that surface resistivity could potentially be used as performance based monitoring of new and older structures. Preliminary results suggest that a conditioning method needs to be applied on-site to approximate water saturation conditions at the elevations of interest.
For corrosion resistant materials exposed to low-temperature atmospheric environments, the corrosion mode of highest risk is expected to be localized corrosion (pitting, crevice, stress-corrosion cracking) due to accumulation of aggressive species within thin solution layers and/or formation of occluded local geometries. The stability of such a localized corrosion site requires that the corroding site (anode) must dissolve at a sufficient high rate to maintain the critical chemistry, and a robust cathodic area (cathode) must exist that can provide sufficient cathodic current. The characteristics of both the anode and the cathode depend on a large number of physiochemical variables (e.g., temperature, ionic concentration, water layer thickness, etc) and electrochemical parameters (i.e., cathodic and anodic polarization behavior). The effects of all these parameters add significantly to the dimensionality of the problem and a systematic study of these parameters is thus more tractable computationally than experimentally. The objective of this study was to computationally characterize the stability of such a local corrosion site and explore the effects of physiochemical and electrochemical parameters on that stability. The overall goal is to contribute to the establishment of a scientific basis for the prediction of the stabilization of localized attack on wetted, corrosion resistant material surface. A localized corrosion site, illustrated in Figure 1, consists of two parts: (a) the external wetted surface (cathode) and (b) the crevice (anode). This study computationally separated the two and modeled them individually, linking them through the imposition of a common fixed potential at the junction point (i.e., the mouth of the crevice). An objected-oriented computational code, CREVICER, developed at UVa, was extended to study separately both the wet surface (cathode) and the crevice (anode). SS316L was chosen as the material of interest.
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Samples with two different binary blended concrete mixes were prepared, one containing cement replacement of 50% slag (referred here as SL mix) and the other containing cement replacement of 20% fly ash (termed here as FA mix). The water to cementitious ratio used to produce concrete specimens was 0.41. On the top surface of each specimen, various reservoir lengths that ranged from 2.5 cm to 17.5 cm were fitted, and these reservoirs were filled with a 10% NaCl solution. Electromigration was used to accelerate the transport of chlorides, with an applied potential of 9 V at first, and subsequently reduced to 3 V after about a week. The electromigration was applied for a short period (few weeks to a couple of months). For a period of about 1100 days, the corrosion related parameters such as concrete solution resistance, rebar potential, and corrosion current were monitored via the rebar potential measurements, linear polarization resistance (LPR) and electrochemical impedance spectroscopy (EIS) measurements, the latter used only to obtain the solution resistance. The corrosion current values determined through experimental observations were then converted to mass loss using Faraday’s law. The readings of corrosion current values (last 7 sets of readings) as well as the calculated mass loss values were found to be larger for the rebars embedded in specimens prepared with SL mix, followed by rebars embedded in specimens prepared with FA mix. Corrosion current and calculated mass loss values in general tended to increase with increasing solution reservoir lengths. No cracks or corrosion products that reached the surface of the concrete were observed on the specimens for the duration of the reported monitored propagation period. This study offers a framework for future studies on accelerated steel corrosion in concrete.
An Al-Co-Ce alloy system has been developed with two important protection abilities when deployed as a metal coating over AA2024-T3. These alloy coatings can both act as a sacrificial anode and supply soluble ions that could function as inhibitors. In this paper, the electrochemical (or electrolytic) throwing power of such an Al-Co-Ce metallic coating under atmospheric conditions is modeled. The criterion for protection is a galvanic couple potential distribution below the pitting potential of AA2024-T3. The effects of scratch size, pH, chloride concentration, metallic coating composition, and electrochemical kinetics of the materials involved were studied. Substantial sacrificial cathodic prevention of AA2024-T3 scratches could be achieved with Al-Co-Ce alloys with performance superior to conventional Alclad coatings in terms of both extent of polarization and maximum scratch size protected. The behavior of the metallic coating can be tailored and provides the best protection (i.e., largest cathodic polarization of the longest scratch lengths) when it contains a low Co content, is exposed to either high or low pH solutions of low chloride concentration, and the AA2024-T3 scratch exhibits slow cathodic kinetics. The Co content should be minimized, in order to maximize the electrochemical throwing power, but must be sufficient for retention of amorphicity.
As part of the efforts toward achieving bridges with a service life of 100 plus years, a study was initiated almost nine years ago to assess the use of galvanized rebars. Three different reinforcing steel bars were used in this study: regular carbon steel rebar, galvanized rebar and Zn-4.9Al-0.1 misch metal bath bar “GF” (the last two are Zn coated bars). The specimens used to rank the rebars were ASTM G-109. Several concrete-mixes-series were prepared. Parameters varied: two water/cement ratios and the effect of two admixtures pozzolanic admixtures. Another variable was the shape of the top rebar. In some specimen sets, the specimen had an initial simulated crack. Selected series with galvanized rebars were prepared with the rebar intentionally damage before exposure. Forensic and metallographic examinations were conducted on selected specimens after being exposed for almost nine years. Results of this examination will be presented. As a general summary, a number of the data sets indicated that galvanized bars out-performed black bars, but in certain conditions the performance difference was marginal. The GF bars have exhibited excellent corrosion resistance in the standard and simulated concrete cracked configurations (the only conditions tested for GF bars).
Once corrosion of the reinforcing steel embedded in concrete has initiated, the corrosion propagation period is typically assumed to last five to ten years for carbon steel reinforcement. However, the duration of the corrosion propagation period could be significantly longer depending on the exposure environment, reinforcement diameter, size of the corroding site, concrete cover, and concrete composition (e.g., w/cm, total cementitious content, presence of supplementary cementitious materials), and resistivity (affected by temperature and moisture content). A better understanding of how corrosion propagates could provide better guidance when conducting the assessment and control of corrosion for structures in which corrosion has initiated. Corrosion propagation was investigated on instrumented reinforced concrete pipe segments, after corrosion of the reinforcement had initiated. The specimens were exposed to lab humidity and temperature for several months, after corrosion initiated. During this time, corrosion continued. It was then decided to apply a current equivalent to 0.5 μA/cm2 via a galvanostat (in some cases this current density was later increased to 1 and 2.5 μA/cm2) in addition to the naturally occurring corrosion current density. The applied current density assumed that half of the steel area under the reservoir was undergoing corrosion. The current was applied: typically current-on for 11 days and then disconnected for 3 days, and the process was then repeated. The specimens during the accelerated corrosion period were stored in high humidity, and after several cycles, selected specimens were covered with saturated sand while others remained under the high humidity exposure. During the disconnected periods, electrochemical measurements such as corrosion potential, linear polarization resistance, and electrochemical impedance spectroscopy were performed; the latter two tests at least two days after removal of the applied current. Selected specimens were terminated and gravimetric weight loss measured. These weight loss values were compared to the mass loss calculated by using Faradays law obtained from the measured corrosion current.
