Publications

Corrosion of carbon steel rebar in binary blended concrete with accelerated chloride transport

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.

Inhibition of the Oxygen Reduction Reaction on Copper with Cobalt, Cerium, and Molybdate Ions

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.

Critical Concentrations Associated with Cobalt, Cerium, and Molybdenum Inhibition of AA2024-T3 Corrosion: Delivery from Al-Co-Ce(-Mo) Alloys

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...

Coupled Multi-Electrode Investigation of Crevice Corrosion of 316 Stainless Steel and NiCrMo Alloy 625

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 on marine substructures to assess concrete permeability

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.

COMPUTATION MODELING OF LOCALIZED CORROSION STABILITY ON WETTED SS316L AT 25 AND 95 DEGREE C

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.

Corrosion Propagation of Carbon Steel Rebar with Different Concrete Covers and Concrete/Mortar Compositions

The corrosion propagation of steel embedded in concrete is still not well understood. It is known that corrosion products build up and eventually cause cracks (when the metal loss reaches a critical penetration xcrit) by exceeding the tensile stress that concrete can support due to the larger volume that the corrosion products occupy. Moreover, it has been reported that the amount of corrosion products that could cause concrete to crack is dependent on the length of the anode (corroding site), rebar diameter, and the concrete cover thickness. In this project, three types of specimens were investigated. Specimen type 1 contained a #3 rebar with 0.8 or 1.2 cm cover and the rebar was embedded in mortar; a w/cm of 0.38 was used for most specimens and a few specimens were prepared with w/cm of 0.45. Specimen type 2 contained #5 rebar, a single rebar with a concrete cover of 5 cm, and two different concrete compositions with a w/cm of 0.41 (OPC and OPC+ 20% Fly Ash). These specimens have been within the corrosion propagation period for over three years. The third type of specimens are instrumented segments of reinforced concrete pipes, initially with no chlorides, but chlorides were transported via migration to initiate corrosion after a short period of time. The reinforced concrete pipes contained steel strands that range from 4.5 to 5.5 mm in diameter. The propagation period reported in here on all of the different type of specimens was at least 600 days. In just a few cases corrosion products were observed at the concrete/mortar surface and only some of the mortar specimens and one of the type 3 specimens showed cracks after corrosion was propagating for at least a year. Linear polarization, corrosion potential and electrochemical impedance spectroscopy tests were used to periodically monitor some of the specimens. Selected specimens were terminated and forensic examination was performed.

Chloride Diffusivity and Resistivity of Cured and Mature Binary/Ternary Concrete [Final Report]

Coupled Multi-Electrode Investigation of Crevice Corrosion of 316 Stainless Steel and NiCrMo Alloy 625

not Available.

Chloride Diffusivity through Partially Saturated, Binary-Blended Concrete

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Long-Term Corrosion Behavior of Reinforced Concrete: Impact of Supplementary Cementitious Materials and Reservoir Size Under Accelerated Chloride Ingress

This study investigates the long-term corrosion behavior of reinforced concrete (RC) under accelerated chloride exposure for about 1600 days, using electrochemical methods like galvanostatic pulse (GP) testing. Two concrete mixes (T1 and T2), incorporating distinct supplementary cementitious materials (SCMs), were evaluated to determine their performance in aggressive environments. Specimens with varying reservoir lengths were exposed to a 10% NaCl solution (by weight), with electromigration applied to accelerate chloride transport. Electrochemical assessments, including measurements of rebar potential, concrete solution resistance, concrete polarization resistance, corrosion current, and mass loss, were conducted to monitor the degradation of embedded steel. The findings revealed that smaller reservoirs (2.5 cm) significantly restricted chloride and moisture penetration, reducing corrosion, while larger reservoirs (10 cm) resulted in greater exposure and higher corrosion activity. Additionally, T1 mixes (partial cement replacement with 20% fly ash and 50% slag) showed higher corrosion currents and mass loss, whereas T2 mixes (partial cement replacement with 20% fly ash and 8% silica fume) demonstrated enhanced matrix densification, reduced permeability, and superior durability. These results underscore the importance of mix design and exposure conditions in mitigating corrosion, providing critical insights for improving the longevity of RC structures in aggressive environments.

Probabilistic Modeling of the Relationship between Concrete Crack Width and Corrosion-Induced Mass Loss of Steel Bar

Corrosion-induced concrete cover cracking generally experiences two stages: initial stage when cracks are developed from the bar until reaching the concrete surface; propagation stage in which cracks connect and widen on the concrete surface. A lot of studies have been conducted to investigate corrosion-induced concrete cracking. However, most of them are focused on the initiation stage and less work are done in the propagation stage, particularly on the relation between the crack width and the cross-sectional area loss of steel bars. The relation between the concrete crack width and the area loss of steel bar is not deterministic, due to the variation of environmental parameters such as temperature, moisture, availability of oxygen, and the non-homogeneity of concrete cover, passive film, and metallurgical properties of steel bars. Therefore, probabilistic method will be more realistic than the deterministic approaches. In this study, the relation between concrete crack width and corrosion-induced mass loss of steel bar was studied in a probabilistic way. Concrete block specimens containing steel bars were prepared and subjected to accelerated corrosion test (ACT). Three concrete cover thicknesses were considered including 25.4 mm, 50.8 mm and 63.5 mm. The ACTs are terminated when the corrosion of steel bar reached to different levels ranging from 0% to 30% mass loss. The crack width is measured using a crack meter and the residual area of corroded steel bars is determined with a 3D laser scan. For a fixed corrosion loss, the corresponding crack width was fitted with a probabilistic density function (PDF). Probabilistic analysis results showed that normal distribution function best fitted the distribution of crack width. The mean crack width increases logarithmically with an increase in the corrosion-induced area loss of steel bars.

Subcomponent Validation of Composite Joints for the Marine Energy Advanced Materials Project

The Marine Energy Advanced Materials project is an ongoing multi-year, multi-lab project with the main goals of addressing barriers and uncertainties facing marine energy developers in adopting advanced materials for structural applications. NREL's goals of the project were to address subcomponents testing needs for marine energy materials, to improve understanding of design allowables at the full-scale and provide near net-scale static and fatigue data of composite subcomponents using materials applicable to the marine energy industry. In the long term, the test method development and data generated would be used to inform standards development. This report outlines perhaps one of the largest-scale studies conducted with regards to saltwater conditioning of various composite material subcomponents and their subsequent structural validation, specifically directed at the marine renewable energy industry. A variety of fiberglass composite panels with epoxy and vinyl ester epoxy resin systems were manufactured at Montana State University, which were then used to manufacture an array of different types of subcomponent test specimens at the National Renewable Energy Laboratory's Flatirons Campus. These subcomponents were in the form of T-bolt and double-ended-insert specimens, which were intended to represent bonded and mechanical bolted connections for thick composite laminates, metal-metal and composite lap shear specimens to evaluate adhesion of constituent materials, and adhesive beam-shear specimens as part of an effort to better evaluate the characteristics of thick adhesive bondlines. Overall, the materials used were fiberglass reinforced epoxy and vinyl ester matrix composites, epoxy and methacrylate adhesives, and 316 and 2507 stainless steels. Specimens were then conditioned in salt water at various temperatures and for various periods of time at Florida Atlantic University and Pacific Northwest National Laboratory. All specimens were then mechanically characterized and validated using various test methods under static and fatigue loading conditions at NREL's Structural Technology Laboratory. Throughout the conditioning and mechanical validation process, valuable experience was gained, which will help guide future test method development for marine energy materials. In many instances, the results indicated similar observations as to what had been observed during previous coupon scale characterization efforts that provided a vital understanding of the scale up process. However in some instances, unexpected phenomena were observed, such as interactions between the adhesives and 316 steel. Furthermore, some materials exhibited significant degradation due to the saltwater conditioning. Ultimately, this report provides a detailed summary of the specimens that were designed, the subcomponent test methods that were developed, and the results that were generated, which will serve as important guidance for marine renewable energy developers and researchers for future structural designs and validation.

Investigation of Crevice Corrosion of AISI 316 Stainless Steel and Ni-Cr-Mo Alloy 625 Using Coupled Multi-Electrode Arrays

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°C was found to readily initiate close to the crevice mouth (i.e., xcrit ≈ 0) at modest applied potentials (e.g., Eapp=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., Eapp=50 VSCE). The local crevice current density increased dramatically over a short period to reach a limiting value in both cases. The ramification of the larger critical depth for Ni-Cr-Mo alloys towards crevice corrosion susceptibility is also discussed.

Corrosion of carbon steel rebar in binary blended concrete with accelerated chloride transport

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.

Electrochemical Sacrificial Cathodic Prevention Provided by an Al-Co-Ce Metal Coating Coupled to AA2024-T3

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.

Review of Galvanized Rebar Performance on G-109 Specimens after 9 Years

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).

Corrosion Propagation under Moderate Accelerated Conditions

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.