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The stability of localized corrosion sites on SS 316L exposed to atmospheric conditions was studied computationally by considering the wetted cathode and the crevice anode separately and linking them via a constant potential boundary condition at the mouth of the crevice. The limitations on the ability of the cathode that are inherent due to the restricted geometry were assessed in terms of the dependence on physical and electrochemical parameters (temperature, electrolyte layer thickness, solution conductivity, and the size of the cathode). An analysis of variance showed that the solution conductivity and the length of the cathode were the most important parameters in determining the total cathodic current capacity of the external surface. A semi-analytical equation was derived for the total current from a restricted geometry held at a constant potential at one end.
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...
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The determination of concrete resistivity via the Wenner probe has become an established non-destructive technique either as to verify performance based concrete quality or to assess the chloride diffusivity of existing concrete structures. However, various factors can result in misinterpretations when taking the resistivity measurement. In this study, the finite element method (FEM) is employed to assess the effects of specimen geometry, specimen size, rebar presence, cover depth, multi-layered resistivity, and the combined effects of these factors. The findings confirm that the influence can be quantified by FEM computations to obtain normalization parameters (i.e. cell constants) or to better interpret field resistivity measurements.
The effect of , , and inhibitor ions on the oxygen reduction reaction (ORR) was experimentally investigated on AA2024-T3 and selected castings containing intermetallic phases (i.e., Al–Cu–Mg and Al–Cu–Mn–Fe). All the inhibitors were found to reduce both the activation-controlled and mass-transfer-limited current densities associated with ORR. Molybdate ions were found to be the most effective cathodic inhibitors, followed by the cerium ions. Cobalt(II) ions were found to be effective, as well. The effect of inhibitors was modeled by considering three possible cases using a heterogeneous electrode model including an array of active electrodes embedded in an inactive matrix: (i) reduction of the size of electrochemically active sites, (ii) reduction of the spatial density or increase in the spacing between active sites, and (iii) formation of permeation barrier to diffusion. These models were found to be consistent with the experimental findings.
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Specimens with binary and ternary concrete mixtures were prepared. The specimens were reinforced with a #3 rebar and have 0.75 cm concrete cover. Electromigration was used to accelerate chloride transport, this lasted anywhere between a week to a few months. The effect of rebar length under the reservoir and concrete composition was investigated. This paper presents the monitoring via linear polarization resistance and galvanostatic pulse to determine the corrosion current. The solution resistance and rebar potential were monitored for over 600 days. Corrosion in some cases initiated several weeks after removing the electromigration. Selected samples were terminated, only small corrosion spots were found.
Dry-cast Reinforced concrete pipes (RCP) are frequently used as drainage pipes by several state departments of transportation (DOTs) across the United States. Corrosion has been found on culverts at locations close to the ocean where they experience wet/drying cycles of chloride rich solution. However, modest or no corrosion of RCPs have been observed on RCPs placed in soils and exposed at sites with known high chloride concentration and high moisture content. It is frequently assumed that this good performance is due to oxygen concentration limitations at the reinforcement. Another factor contributing to this observation is that on those dry-cast RCPs in which corrosion had initiated the high porosity of dry-cast RCP allows the corrosion products to move through the pore structure without causing cracks or spalls. This paper presents preliminary results of an investigation being carried out to better understand and characterize on-going corrosion on RCP exposed to relevant conditions (concrete in a high moisture content state and/or exposed to low oxygen concentration at the rebar). The results presented here correspond to the methodology developed to accelerate chloride transport as to initiate corrosion within a short period of time (a few days to a few months instead of a several years).
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.
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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.
The electrical resistivity is an important parameter currently used to characterize the durability of reinforced concrete. Concrete resistivity measurements have been correlated to the corrosion rate of depassivated steel reinforcements and to the chloride penetration resistance of concrete. The resistivity of concrete is influenced by a number of factors such as pore structure, ion composition in pore water, cement content and degree of saturation. Concrete resistivity is temperature dependent and thus an increase in temperature leads to a decrease in resistivity. An investigation was carried out to study the influence of temperature on resistivity measured on mature saturated high performance concrete cylinders (fully hydrated or close-to). Measurements were performed on 10 cm diameter ×20 cm concrete cylinders under temperatures ranging from 10°C to 45°C. Results show that temperature has different effects depending on the intrinsic resistivity of concrete. It is concluded that an accurate method can be developed to normalize concrete resistivity measured at different temperatures and converted these resistivity values to a reference temperature.
This report describes the findings of concrete resistivity characterization using the surface resistivity (SR) test method. This characterization was conducted on Florida's new and old coastal bridge structures. The testing took place on partially immersed substructures on more than 60 bridges. The SR measurements were performed in areas above the mean tide line (marine growth). The SR profiles at several locations as a function of elevation were performed using a commercial Wenner probe. This Wenner probe is the same instrument used in Florida Department of Transportation's FM5-578 test method. A resistivity gradient from low to high proceeding from the submerged to atmospheric zone is usually observed. This gradient results from the elevation dependence of moisture saturation and pore solution composition. A conditioning procedure was designed and implemented as part of the field testing to increase the moisture content of the concrete being examined (tidal and splash zone). The characteristic SR after one or two days of monitoring is called herein the SRfield. This value was usually the minimum resistivity value observed at the second or higher examined elevation. During the field trips nominal 2-in. concrete cores were obtained in the vicinity of where the SR profiles were made. These cores were used either to perform wet SR measurements in the laboratory or to obtain chloride profiles. The chloride profiles were then used to estimate the apparent chloride diffusivity. The wet SR was achieved after a few weeks of exposure in a high humidity chamber, and is named herein the SRwet. A correlation between SRfield and SRwet was performed and it was found that SRfield was about 3 times that of SRwet; i.e., no full saturation was obtained with the conditioning method. A correlation was computed between chloride diffusivity (average per component) vs. SRwet. However, due to the field nature of the data there is some scatter, the R-squared varied between 0.62 and 0.69 depending on whether all bridges visited were included or if only a subset was used in the fitting. A second component of this project consisted of experiments on laboratory samples aimed at understanding how the resistivity varies over time depending upon the concrete mix and environmental exposure, as well as in the presence - and absence - of reinforcing steel. Numerical modeling was performed to obtain K (cell constants). The K values were used to normalize the SR measurements performed on laboratory samples. Additionally, numerical modeling was performed to investigate additional scenarios (different concrete cover thicknesses, multiple rebar presence, dimensions of the concrete block interrogated, presence of multiple concrete layers). Very useful insight was obtained from this research effort.
