Conventional and pulse cathodic protection of reinforced concrete: Electrochemical behavior of the steel reinforcement after corrosion and protection

The applicability and efficiency of an alternative for impressed current cathodic protection (CP) for reinforced concrete, based on pulse technology, was investigated. The technique, denoted as pulse CP (pCP), was evaluated on the basis of a comparative analysis to reference (non-corroding), corroding, and conventional CP conditions, in terms of long-term monitoring of electrochemical parameters for the embedded steel with time of corrosion and protection. The hereby reported results are for the total duration of the experiment, i.e., 460 days of conditioning, also presented in comparison with earlier stages. Protection was applied after corrosion was initiated (using corrosion medium of 5% NaCl), at different time intervals (here reported are starting points 60 and 150 days of age). Both CP regimes used current density of 5 or 20 mA/m² steel surface. The pulse CP was applied as a pulse-shaped block current (square wave) with the current itself being the feedback control signal, using 12.5–50% duty cycle at 500 Hz to 1 kHz frequency. Under equal environmental conditions and for a comparatively long period of application, the pulse CP was found to perform as effectively as the conventional CP with regard to electrochemical behavior of the steel reinforcement. Furthermore, the pulse CP technique was found to achieve more rapidly the so called “open circuit potential (OCP) passivity” as a result of an enhanced ion transport (chloride withdrawal) and more favorable cement chemistry (increased alkalinity around the steel reinforcement).     

Development of corrosion sensors for monitoring steel‐corroding agents in reinforced concrete structures

Corrosion sensors were devised to develop a system whereby the depth of chloride permeation from concrete surfaces can be monitored non‐destructively on a real‐time basis using such sensors embedded in cover concrete of reinforced concrete structures. The proposed corrosion sensors were subjected to accelerated corrosion in NaCl solutions, mortar specimens intrinsically containing chlorides, and mortar specimens impregnated with chloride solutions, while recording the changes in the resistance readings. The resistance of sensors increased as the degree of corrosion increased. The time to the first change in the resistance decreased and the corrosion degree and resistance increased as the chloride concentration increased and as the distance from mortar surfaces decreased. It was therefore confirmed that the corrosion sensors are capable of monitoring the depth of chloride permeation with sufficient accuracy.     

Sprayed titanium coatings for the cathodic protection of reinforced concrete

Thermally sprayed titanium coatings were investigated in the laboratory as anodes for the cathodic protection of reinforced concrete. Three proprietary catalyst systems were used to activate the titanium anode coatings. Some experiments were conducted that applied the catalyst as a precoat on the metallizing wires; in other experiments, the catalyst solution was applied onto concrete blocks before or after arc spraying with titanium. The coated reinforced concrete blocks were powered at a constant current density and in a 95% relative humidity for more than 95 days. The driving voltages measured across the samples demonstrated that precoating the catalyst on the titanium wires had little effect on the driving voltage over the recorded lifetime. In other experiments, where the catalyst was directly applied to the surface of the reinforced concrete blocks, only the cobalt oxide catalyst significantly reduced the driving voltage requirements. The cobalt oxide reduced the driving voltages regardless of whether it was applied on the concrete blocks before or after arc spraying with titanium.     

Thermal sprayed titanium anode for cathodic protection of reinforced concrete bridges

Stable operation of cobalt catalyzed thermal sprayed titanium anodes for cathodic protection (CP) of bridge reinforcing steel was maintained in accelerated tests for a period equivalent to 23 years service at Oregon Department of Transportation (Oregon DOT) bridge CP conditions with no evidence that operation would degrade with further aging. The cobalt catalyst dispersed into the concrete near the anodeconcrete interface with electrochemical aging to produce a more diffuse anode reaction zone. The titanium anode had a porous heterogeneous structure composed of α-titanium containing interstitial oxygen and nitrogen, and a fee phase thought to be Ti(O,N). Splat cooling rates were 10 to 150 K/s, and microstructures were produced by equilibrium processes at the splat solidification front. Nitrogen gas atomization during thermal spraying produced a coating with more uniform composition, less cracking, and lower resistivity than using air atomization.     

Quantitative measurements of corrosion rate of reinforcing steels embedded in concrete using polarization resistance measurements

Up to this time all the methods to measure the corrosion rate of reinforcing steels embedded in hardened concrete have been of the destructive type, which requires much time and materials and makes the full scale study of the phenomenon difficult. The authors have applied the polarization resistance method to bars embedded in hardened mortar and immersed in Ca(OH)₂-saturated solution, and have found an acceptable agreement between the gravimetric and the electrochemical weight loss data.     

Embeddable reference electrodes for corrosion monitoring of reinforced concrete structures

Mixed‐metal oxide (MMO), graphite and laboratory‐made Ag/AgCl electrodes were electrochemically characterized to be used as reference electrodes embedded in concrete structures. Electrodes were studied in both, aqueous solutions of pH ranging from 7 to 13.5 and embedded into cement mortars; and the electrochemical studies were carried out in the absence and presence of chloride ions. Potential evolution, polarisation behaviour, galvanostatic pulse response and impedance characteristics of the electrodes were carried out in aqueous solutions. Besides, the electrochemical stability of the electrodes embedded in mortar was studied for an exposure period of two years. It was found that the MMO pseudo‐reference electrode is pH‐sensitive, the graphite pseudo‐reference electrode is oxygen sensitive and the Ag/AgCl pseudo‐reference electrode is chloride sensitive. Then, regarding the corrosion monitoring of steel rebars, care should be taken to avoid misleading interpretations of the corrosion potential measurements. However, any of them can be used to measure the corrosion rate of the rebars by means of traditional electrochemical techniques.     

海工钢筋混凝土的腐蚀与防护

海水具有很强的腐蚀性。如果不采取防护措施，海工钢筋混凝土结构会受到严重腐蚀。本文结合当前现有研究成果，对海洋环境下钢筋混凝土结构的腐蚀特征和防护技术进行了论述。     

An embedded multi‐parameter corrosion sensor for reinforced concrete structures

A prototype of an embedded corrosion sensor has been developed for assessing the corrosion status of reinforcing steel bar (rebar) in concrete. The integrated sensor unit includes an Ag/AgCl probe, a metallic oxide probe, a multi‐electrode array sensor (MAS), and a four‐pin (Wenner) array stainless steel electrode for chloride content, pH, microcell corrosion current, and localized concrete resistivity measurements, respectively. A stable solid probe was used as the reference probe in this unit to express the potentiometric measurement of chloride content and pH probes. In this study, the chloride and pH probes were calibrated in simulated pore solutions (SPSs) regarding temperature and pH fluctuations. The corrosion current results of the MAS probe in SPSs matched very well with those obtained by the linear polarization resistance technique, which was conducted on companion carbon steel specimens. A sensor prototype was embedded into a paste cylinder for long‐term performance evaluation. Up‐to‐date results show that the sensor probes exhibit excellent sensitivity and reliability through 1 year of monitoring. Continuous monitoring in the laboratory for extended periods is underway.     

Assessing corrosion risk in reinforced concrete using wavelets

Corrosion potential measurements were analyzed using the continuous wavelet transform (CWT). The corrosion potentials estimate the probability of corrosion of steel embedded in concrete. The CWT of the corrosion potential data estimates the behaviour in time of the energy distribution associated with the corrosion process. The results obtained indicate that CWT-based ratios can be successfully applied to better understand the different processes involved in the corrosion phenomenon, such as the cracking of concrete.     

Throwing power of cathodic prevention applied by means of sacrificial anodes to partially submerged marine reinforced concrete piles: Results of numerical simulations

The paper deals with the determination of current and potential distribution in reinforced concrete elements partially submerged in seawater aimed at predicting the throwing power of cathodic prevention applied by means of sacrificial anodes. Experimental results from previous laboratory tests showed that the throwing power of cathodic prevention is higher compared to that of cathodic protection [1]. In order to extend the results obtained on small-scale specimens to elements of higher dimensions, FEM numerical simulations of potential distribution were carried out. Several cases were considered, representative of conditions differing in electrochemical behaviour of steel bars, geometry of the pile and of sacrificial anodes, concrete resistivity. The results allowed to discuss the role of different factors on the throwing power that can be reached by using sacrificial anodes immersed in the seawater to protect reinforcing steel bars in the emerged part of a pile.     

Considerations on reproducibility of potential and corrosion rate measurements in reinforced concrete

This communication analyses information supplied by the electrochemical parameters related to rebar corrosion in reinforced concrete structures (RCS). Corrosion potential and corrosion current density are determined for different sets of conditions. Tests are performed to gather data on conflictive aspects of the two electrochemical parameters, with regard to evaluating the results of RCS inspections. Consideration is made of the limitations of potential measurements if not accompanied by complementary indications such as concrete resistivity, rebar surface area involved in the measurements, or the instrumentally determined corrosion current. The capacity of galvanostatic pulses applied directly on large RCS to offer a reliable guide to corrosion rate of steel reinforcements is discussed.     

Electrochemical characteristics of stainless steel using impressed current cathodic protection in seawater

Stainless steels such as STS 304, 316 and 630 are frequently used as shaft materials in small fiber reinforced polymer (FRP) fishing boats. If the shaft material is exposed to a severely corrosive environment such as seawater, it should be protected using appropriate methods. The impressed current cathodic protection was used to inhibit corrosion in shaft materials. In anodic polarization, passivity was remarkably more evident in STS 316 stainless steel than in STS 304 and STS 630. The pitting potentials of STS 304, 316, and 630 stainless steels were 0.30, 0.323, and 0.260 V, respectively. The concentration polarization due to oxygen reduction and activation polarization due to hydrogen generation were evident in the cathodic polarization trends of all three stainless steeds. STS 316 had the lowest current densities in all potential ranges, and STS 630 had the highest. Tafel analysis showed that STS 316 was the most noble in the three. In addition, the corrosion current density was the lowest for STS 316.     

An economic solution for the cathodic protection of concrete columns using a conductive tape system

Corrosion and spalling of reinforced concrete columns particularly in tidal seawater zones is a major concern worldwide. A greater emphasis is being given to the maintenance and preservation of existing structures rather than the expensive alternative of replacement. Cathodic protection has been identified as one of the most effective means of arresting corrosion on steel reinforcement. This paper describes a newly developed technique of applying cathodic protection to steel reinforced concrete. The components comprise of conductive tape and mixed metal oxide coated titanium mesh anode (CAT) system. Protection is provided with an even current distribution over the surface via the conductive tape. An extremely long system life is predicted due to the low current densities involved and the elimination of shotcrete type cementitious overlays which tend to be the weak link. A major advantage of the CAT system is that it does not require the use of specialised equipment and that installation time is minimal. Two trials performed on road bridges in Victoria and Queensland, Australia are described in detail. The CAT systems were installed to protect the tidal zones and above. Polarisation effects and the possibility of current “dumping” in submerged zones were investigated. The long term evaluation and assessment of the performance of the system is an ongoing process. Monitoring will be performed on a regular basis over the next few years.     

Alternative methodology for on site monitoring of corrosion and remediation of reinforced concrete

Abstract

Difficulties associated with the interpretation of site data collected over long periods of time from commonly used corrosion monitoring techniques for steel reinforcement in concrete, such as corrosion potential measurements and linear polarisation resistance, often make it difficult to assess accurately the extent of corrosion. An alternative methodology for the interpretation of data is proposed, based upon a model of the quality of the passive film on the steel surface. This model leads to a representation of the corrosion state by means of the relationship, over a long period of time, between the corrosion potential and the logarithm of the linear polarisation resistance. For the reinforced concrete panels tested in this study, data points representing this relationship closely fitted a family of results. This led to the development of a so called 'monitoring control diagram', MCD, in which for a fixed geometry and fixed experimental conditions, a relationship between the corrosion potential and polarisation resistance of steel exists. The establishment of an MCD may enable the development of a useful monitoring tool.     

Development of a new combined corrosion protection system for chloride‐contaminated reinforced concrete structures

Chloride‐induced damage of reinforcing steel is especially for parking garages and bridges often very severe as large amounts of chlorides act on horizontal surfaces which could lead to fast ingress of these detrimental ions up to the level of the reinforcement and subsequently to high rates of corrosion. In order to avoid the disadvantages of conventional rehabilitation (unreliable prognosis with patch repair or high costs and regular maintenance with cathodic protection using impressed current) a new combined protection system was developed where the principle of drying out the concrete (by means of a surface protection system) is combined with a temporary cathodic protection (by means of a sprayed zinc layer) during the transitional period of the drying out process. This new system was tested both in the laboratory and on‐site at a pilot application. Based on the results obtained the possibilities and limitations of the new system are discussed in this paper.     

A galvanic sensor system for detecting the corrosion damage of the steel embedded in concrete structures: Laboratory tests to determine the cathodic protection and stray-current

In order to evaluate the possible application of a galvanic sensor for cathodic protection (CP) and straycurrent monitoring of steel embedded in concrete structures, the correlation of sensor current to protection abilities (protection potential/current) and stray-current was investigated by galvanostatic tests that simulated the CP and stray-current. The results revealed a good correlation between the sensor current and the protection abilities or stray-current in terms of the sign as well as magnitude. Thus, the galvanic sensor is proposed as an effective tool for the quantitative determination of the effectiveness of CP or of the interference effect of stray-current.     

Electrochemical behavior of microbiologically influenced corrosion on Fe_3Al in marine environment

In this article,microbiologically influenced corrosion behavior of Fe3Al intermetal-lic compound in microorganism culture medium has been investigated by using weight loss methods,electrochemical techniques,and electron microscopy.Polar-ization curves showed that a sharp electrical current peak caused by surface pitting could be observed after Fe3Al electrodes were immersed in culture medium for 15 days when the polarization potential was about-790 mV vs SCE.Based on the electrochemical impedance spectrosco...