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Carbonation‐induced corrosion of steel in concrete can allow for premature degradation of structures. Corrosion probes in health monitoring systems can assess concrete carbonation and steel corrosion rates. The electrochemical noise (EN) technique has advantages for corrosion sensing. Instrumented concrete columns were fitted with a carbonation chamber for accelerated testing. EN was assessed through statistical evaluation of noise time signatures, noise resistance, and spectral analysis. The mean noise potential for the electrodes showed electronegative potential and correspondingly high rms noise current, indicative of corrosion activation in carbonated concrete. The estimated corrosion rates obtained from the noise impedance were comparable to those resolved from the polarization resistance and noise resistance. The shot noise analysis indicated isolated spontaneous noise events associated with the activation of local steel anodes. The outcomes of the testing indicate that the placement of low‐cost sensors and passive EN measurements can be used to monitor the onset of carbonation‐induced corrosion of steel in concrete and provide estimates on corrosion rates. [ABSTRACT FROM AUTHOR]

The corrosion of steel in post-tensioned tendons has been associated with deficient grout materials containing high free sulfate ion concentrations. In a Florida bridge in 2011, tendon corrosion failures occurred for a prepackaged thixotropic grout that had developed material segregation. However, the available grout and corrosion testing prescribed in material specifications, such as grout bleed water testing, was not able to identify the propensity or modality for the grout deficiencies and the associated steel corrosion that was observed in the field. It was of interest to identify corrosion testing methods that could prescribe grout resistance to segregation-related deficiencies that can form by aberrations in construction. The objectives of the work presented here included (1) characterizing the development of physical and chemical grout deficiencies due to excess mix water and water volume displacement, (2) developing small scale test methodologies that identify deficient grout, and (3) developing test methodologies to identify steel corrosion in deficient grout. The inverted-tee test (INT) and a modified incline-tube (MIT) test were assessed and both were shown to be useful to identify the robustness of grout materials to adverse mixing conditions (such as overwatering and pre-hydration) by parameters such as sulfate content, moisture content, electrical resistance, and steel corrosion behavior. It was shown that the different grout products have widely different propensities for segregation and accumulation of sulfate ions but adverse grout mixing practices promoted the development of grout deficiencies, including the accumulation of sulfate ions. Corrosion potentials of steel < −300 mVCSE developed in the deficient grout with higher sulfate concentrations. Likewise, the corrosion current density showed generally high values of >0.1 μA/cm2 in the deficient grouts. The values produced from the test program here were consistent with historical data from earlier research that indicated corrosion conditions of steel in deficient grout with >0.7 mg/g sulfate, further verifying the adverse effects of elevated sulfate ion concentrations in the segregated grout. [ABSTRACT FROM AUTHOR]

The safety, integrity, and longevity of steel bridge elements are affected by various environmental factors, such as moisture, atmospheric pollutants, and temperature. Protective coatings of steel bridge elements are especially sensitive to the service environments (e.g., atmospheric environments, water environments) of bridges, as many environmental stressors may accelerate premature failures of coatings. By leveraging the data on both bridge-related features (e.g., bridge age, type of service under bridge) and environmental features (e.g., chloride, moisture, atmospheric pollutant, temperature), this study focuses on bringing a data-driven understanding of steel bridge coating deterioration patterns and how the service environments of bridges may impact such patterns. Steel bridge coating performance prediction (SBCPP) models were built based on multilayer perceptron (MLP)–based artificial neural network (ANN) algorithm to predict and assess the coating conditions of girder elements of steel bridges in Florida. The results show that the SBCPP model with the best performance can precisely predict steel bridge coating conditions with a mean absolute error (MAE) of 0.0807. As compared to the models that do not account for environmental features, the performance of the proposed SBCPP models was significantly improved. Shapley additive explanations (SHAP) analysis was further conducted to interpret and analyze the influences of input features on the performance of the SBCPP model. The study offers an effective decision-making tool that has the potential to benefit state transportation agencies by allowing for easier and more efficient analysis or prediction of steel bridge coating performance. This study proposes data-driven models that analyze and predict the coating conditions of steel bridge elements based on the data of bridge-related features (e.g., bridge age, average daily traffic, type of service under bridge) and environmental features (e.g., chloride, moisture, atmospheric pollutant, temperature), thus providing knowledge and insights on corrosion-induced coating degradation for steel bridges in Florida. The proposed models serve as the foundations for an automatic coating performance assessment and prediction tool that can help state transportation agencies and other bridge owners easily evaluate the coating conditions of their steel bridges and identify those bridges that are in critical maintenance needs. Inspection of coating conditions traditionally requires significant manual efforts, which are expensive, time-consuming, and cause safety concerns. An automatic tool based on the proposed models can quickly and easily analyze the element-based coating conditions while considering the impacts of the service environments. By using the tool, a bridge owner can quickly identify those bridges that require more attention or funding support and decide which bridges should be given priority in terms of inspection, maintenance, and/or repair. Hence, acting as the foundation of such a decision support tool, the proposed work has the potential to reduce field-level coating inspection costs, efforts, and risks and enhance the efficiency of maintenance and repair-related decision-making. [ABSTRACT FROM AUTHOR]

Even with the continuous development of coating technologies, coating systems are susceptible to corrosion-induced premature failures and unable to meet the anticipated service life. Coating premature failures will negatively impact the safety, integrity, and longevity of steel bridge structural elements. The advancement of the data analytics approach (e.g., machine learning) offers an opportunity to leverage the wealth of historical bridge inspection and maintenance data collected by Departments of Transportation to evaluate coating conditions of steel bridges effectively and efficiently. This paper focuses on presenting a data-driven study that analyzes the conditions of coating systems of steel bridges in the state of Florida. Three machine learning algorithms were used in developing models that can be used to analyze steel bridge coating conditions based on data collected from the Bridge Management System of the Florida Department of Transportation. The result showed that the machine learning–based models were able to effectively predict steel bridge coating conditions. The k -nearest neighbor (KNN) regression algorithm offered the best performance. Although the approach was currently applied to the steel bridges of Florida, it can be easily replicable for similar data sets from other states. The research contributes to the body of knowledge by offering a data-driven understanding of coating performance of steel bridge elements. The research has the potential to offer a valuable decision-making tool for transportation agencies to effectively and easily analyze or predict steel bridge coating conditions. [ABSTRACT FROM AUTHOR]

Post-tensioned (PT) construction incorporating bonded tendons with cementitious grouts has been used for highway bridges. The tendon duct and the encapsulating grout materials provide barrier corrosion protection for the embedded high-strength steel strand. Although generally used in good engineering practice, cases of PT tendon corrosion have been documented relating to inadequate detailing for joints and development of grout bleed water. Recently, in the past several years, unexpected severe localized strand corrosion has related to the segregation of thixotropic grouts. In the latter case, thixotropic grouts (that have been developed to mitigate grout bleeding) formed physical and chemical deficiencies that have been characterized to have high moisture content and elevated sulfate ion concentrations. The early presence of elevated sulfate ion concentrations in the deficient grout hinders stable steel passivation. The corrosion mechanism can be complicated due to the compounding effects of physical grout deficiency, moisture content, pore water pH, and the presence of sulfate ions. There remains interest to reliably assess corrosion of PT tendons with deficient grout. A review of electrochemical techniques and test methods used in earlier research by the authors to identify the role of sulfates on localized steel corrosion in alkaline solutions is presented. It was evident that different testing methods can reveal various aspects of the corrosion of strands in the deficient PT grout. The open-circuit potential and linear polarization method could differentiate corrosion activity between hardened and deficient grout environments but did not reveal the development of localized corrosion. Electrochemical impedance spectroscopy was useful to identify grout deficiencies by the differentiation of its bulk electrical properties. Potentiodynamic polarization and electrochemical noise technique were used to identify metastable and pitting in alkaline sulfate solutions representative of the deficient grout pore water. [ABSTRACT FROM AUTHOR]

Research on the effects of sulfate ions on steel corrosion has been conducted in response to the observations of premature localized corrosion of steel strands in cementitious grouts in posttensioned bridge construction. Electrochemical noise (EN) was shown to be an effective technique to assess the development of localized corrosion of steel in the alkaline sulfate solution. General statistics of the EN potential and current time signatures revealed the negative effect of elevated sulfate concentrations and the development of pitting events. Spectral analysis indicated an increase in the characteristic charge and decrease in characteristic frequency with sulfate ion concentration, whereas an increase in the overall corrosion rate was observed, indicating the development of pitting corrosion. Pitting events could be sustained in solutions above 10 g Na2SO4/L H2O and more extensive localized corrosion developed above 20 g Na2SO4/L H2O. [ABSTRACT FROM AUTHOR]

Steel piles in a Florida bridge showed severe localised corrosion uncharacteristic of the general corrosion typically found in marine environments. Sampling from the water and the steel pile surface showed presence of bacteria associated with microbiologically influenced corrosion, MIC. Coincident heavy marine growth was observed. The interactions of marine macro- and microorganisms set up conditions where the severe corrosion occurred. The initiation of macrofouling require initial biofilm presence, but the subsequent fouling crevice environments would sequentially promote enhanced microbe growth (such as sulphate reducing bacteria, SRB) to support MIC. Antifouling and antibacterial coatings that have been developed to manage macrofouling may be applicable to prevent MIC. However, long-term durability of the mitigation coating technology can be compromised. The research objective was to identify the efficacy of biocides in an antifouling coating to mitigate microbial activity that are associated with fouling and MIC. Research included laboratory and field examination of a commercially-available antifouling coating in presence of SRB. It was confirmed that degradation of the coating would result in reduced antibacterial and antifouling efficacy and facilitation of SRB growth and marine fouling. [ABSTRACT FROM AUTHOR]

• Barrier protection from galvanized steel in sulfate-rich grout can be compromised. • Sulfates in alkaline solution develop poor coverage of calcium hyroxyzincate. • Corrosion development of galvanized steel captured by EN technique. Corrosion mitigation strategies for structural steel bridge elements including post tensioned steel components include the use of galvanized steel. The zinc alloy layers and subsequent precipitation of a dense surface oxide in alkaline environments provide beneficial barrier protection to mitigate corrosion. However, severe corrosion of galvanized steel components in contact with sulfate-rich deficient cementitious grout was documented to occur in less than 8 years of bridge service. Electrochemical testing and material characterization showed that the presence of sulfates in alkaline solutions allow for prolonged zinc activity and hindered passivation by the incomplete surface coverage and the precipitation of large sized calcium hydroxy zincate. OCP, LPR, and electrochemical noise (EN) testing showed greater corrosion activity of galvanized steel in chloride and sulfate solutions. EN identified local corrosion activity of the zinc associated to the porous nature of the surface oxide layer. [ABSTRACT FROM AUTHOR]

The three-coat system consisting of a zinc-rich primer, epoxy midcoat, and polyurethane topcoat has been widely adopted for corrosion protection of structural steel bridges. Corrosion mitigation is afforded by the barrier characteristics of the various layers as well as beneficial galvanic coupling of the zinc pigments in the primer to the steel substrate when subjected to corrosive environments such as with moisture ingress and coating defects. The dispersed zinc pigments in the binder require adequate electronic coupling in order to provide the beneficial electrochemical coupling of the zinc to the steel. The application of the electrochemical noise (EN) technique to identify coating corrosion performance was reviewed in controlled laboratory tests. Zinc pigment activation and transition to passive-like conditions in defect and defect-free coating specimens could be identified by EN. The characteristic charge of noise events resolved by shot noise analysis was demonstrated to be related to anodic polarization of extended active zinc pigments adjacent to coating defect sites galvanically coupled to the exposed steel and passivated zinc pigments. Electrochemical noise resistance was shown to convey zinc/steel interfacial behavior in cases with sufficient activity but largely reflects coating barrier quality for intact coatings. • EN time domain statistics differentiated coatings with and without defects. • EN resistance conveys both interfacial and barrier characteristics. • EN technique characterizes zinc pigment corrosion activity. • EN characteristic charge related to polarization from galvanic coupling of zinc and steel [ABSTRACT FROM AUTHOR]

Abstract: Dual polymer/zinc-coated concrete steel reinforcing bar (rebar) is a novel material intended to improve corrosion related durability in marine and deicing salt environments. Severe fabrication bending induces coating breaks and separation from the steel substrate, creating a crevice where some zinc corrosion takes place. EIS measurements to characterize that corrosion revealed spontaneous fluctuations that included variations in the size of the high frequency loop and sometimes strong intermediate frequency dispersion. This investigation examined the underlying causes for that behavior. The fluctuations were explained by formation and episodic release of hydrogen gas in the crevice underneath the disbonded coating, as a product of the cathodic reaction in corrosion of the zinc layer. The gas caused partial occlusion of the crevice and the crevice opening at tears in the coating. Gas occlusion increased the effective electrolytic resistance inside the crevice, and contributed to an enhanced transmission line configuration with associated frequency dispersion, especially notable in the intermediate frequency part of the impedance spectrum. A radial transmission line model was adopted as a simplified abstraction of the system. Properties of the radial transmission line impedance behavior are discussed. The model output replicated the key features of the measured impedance spectrum and its fluctuations, and permitted isolating the low frequency response as the most representative to evaluate corrosion conditions inside the crevice in subsequent research. [Copyright &y& Elsevier]