Electrochemical techniques concrete corrosion

Electrochemical Techniques for Corrosion Evaluation of Reinforcement in Concrete... 

ELECTROCHEMICAL TECHNIQUES FOR CORROSION EVALUATION OF REINFORCEMENT IN CONCRETE... 

Swarup J and Sharma PCI 996 Electrochemical techniques for the monitoring of corrosion of reinforcement in concrete structures Bull. Electrochem. 12 103... 

The electrochemistry of corrosion and the basics of electrochemical potentials and corrosion rate have been discussed in Chapter 7. Here the principles and application of electrochemical inspection techniques for reinforced-concrete structures are given. The different techniques will give different types of information (Figure 16.3). 

R. Myrdal, Evaluation of electrochemical techniques for assessing corrosion of steel in concrete", dissertation for the degree of Doctor Scientarium, University of Oslo, 1997. 

Electrochemical techniques appHed for controlling corrosion of steel in concrete are cathodic protection, cathodic prevention, electrochemical chloride removal and electrochemical reaUcalization. 

Electrochemical techniques are applied in order to avoid corrosion by stopping it, by containing it within reasonable limits or by preventing it. The way to do this, as already stated, is to have a direct current circulate from the concrete to the reinforcement The mechanism by which the circulation of current leads to avoiding corrosion is different in different techniques, as shown in Figure 20.3. Further details are discussed in the following sections. 

D. Btirchler, H. Bohni, Repair of reinforcedelectrochemical techniques - Field experience , in Corrosion of Steel in Concrete, EFC Publication No. 25,... 

It is impossible to remove all the chloride from concrete by the electrochemical method. But the level of chloride in contact with the steel is reduced by 45-95%. Field data have shown that the removal of chloride by electrochemical technique results in stopping corrosion for 8 years. It is predicted by FHWA that the electrochemical method of removal of chloride will extend the life of bridges by as much as 20 years (31). About 372,000 nP (4,000,000 ft ) concrete has been treated by this method. 

A comprehensive Concrete Repair Manual has been developed by ACI in collaboration with BRE, ICRI and the Concrete Society (ACI, 2002). This includes the ACI, Concrete Society, BRE and ICRI guides on condition evaluation and diagnosis, patch repairing and overlaying, as well as guidance documents on protection and corrosion management. Concrete Society (1991) is part of the manual. The manual also includes Corrosion Prevention Association (CPA) monographs on electrochemical techniques, but not NACE recommended practice or technical reports. 

If an electrochemical technique is being used then repairs only need to reinstate damaged concrete. A clean rebar surface is needed and a simple patch to rebar depth in cracked, spalled and delaminated areas will prepare the structure for the application of the anode. In some cases the anode and overlay will fill the excavated areas as a single operation. Only a minimal repair is required as shown in Figure 5.1 becau.se the treatment itself deals with the corrosion. The repair materials must be compatible with the electrochemical treatment. These issues are fully discussed in Chapter 6. 

A simplification of the polarization resistance technique is the linear polarization technique in which it is assumed that the relationship between E and i is linear in a narrow range around E . Usually only two points ( , 0 are measured and B is assumed to have a constant value of about 20 mV. This approach is used in field tests and forms the basis of commercial corrosion rate monitors. Rp can also be determined as the dc limit of the electrochemical impedance. Mansfeld et al. used the linear polarization technique to determine Rp for mild steel sensors embedded in concrete exposed to a sewer environment for about 9 months. One sensor was periodically flushed with sewage in an attempt to remove the sulfuric acid produced by sulfur-oxidizing bacteria within a biofilm another sensor was used as a control. A data logging system collected Rp at 10-min intervals simultaneously for the two corrosion sensors and two pH electrodes placed at the concrete surface. Figure 2 shows the cumulative corrosion loss (Z INT) obtained by integration of the MRp time curves as ... 

Monitoring of the electrochemical potential of steel reinforcement in concrete is a well established technique for assessing the severity of corrosion and for controlling cathodic protection systems. A reference electrode is the electrochemical device used for measuring these potentials. The reference electrode is either placed on the concrete surface during the measurements or permanently embedded in the concrete in close proximity to the steel. The latter technique enables remote long-term monitoring. 

Other workers have published improved procedures for inspecting both reinforced concrete and prestressed concrete structures with regard to determination of the embedded steel components [110]. A prototype ultrasonic procedure was developed to determine the condition of prestressed and pretensioned tendons in concrete. The application of electrochemical surface-mounted systems for estimating the rate of corrosion of reinforcing steel and other embedded steel components in large concrete structures was described using this technique. 

Electrical current flow by ion migration in concrete is important for electrochemical rehabilitation techniques such as chloride removal (Chapter 20), but also for (macrocell) corrosion processes (Chapter 8). 

S. Feliu, J. A. Gonzales, C. Andrade, Electrochemical methods for onsite determinations of corrosion rates of rebars , in Techniques to Assess the Corrosion Activity of Steel Reinforced Concrete Structures,... 

Electrochemical realkalization (RE) and electrochemical chloride removal (CE) can be applied to structures in which corrosion has not or has already initiated. They are techniques aimed at modifying the composition of concrete that is carbonated or contains chlorides, in order to restore its original protective characteristics. 

The corrosion rate is probably the nearest the engineer will get with currently available technology to measuring the rate of deterioration. There are various ways of measuring the rate of corrosion, including AC Impedance and electrochemical noise (Dawson, 1983). However, these techniques are not suitable for use in the field for application to the corrosion of steel in concrete so this section will concentrate on linear polarization, also known as polarization resistance or LPR, and will discuss various macrocell or galvanic current measurement techniques. 

Feliu, S., Gonzalez, J.A. and Andrade, C. (1995). Electrochemical Methods for onsite Determination of Corrosion Rates of Rehars, in Symposium on Techniques to Assess the Corrosion Activity of Steel in Reinforced Concrete Structures, December 1994, American Society for Testing and Materials. 

Concrete Bridge Protection and Rehabilitation Chemical and Physical Techniques—Corrosion Inhibitors and Polymers. Discusses the improvement of existing non-electrochemical methods for protecting and rehabilitating chloride-contaminated concrete w ith and without concrete removal and the development of new methods. Five corrosion inhibitors were evaluated and service lives were estimated for the two most effective treatments. Asphalt Portland cement concrete composite (APCCC) was designed and evaluated, and compared with hot-mix asphalts and Portland cement concrete for strength properties, resistance to freeze-thaw and resistance to chloride intrusion. 248 pages. SHRP-S-666... 

Low Resistance Current Paths. An indirect use of zinc for corrosion protection is to provide a low resistance path for impressed current protection of concrete bridge structures with uncoated steel rebar. Electrochemical protection of steel rebar in concrete was developed as a repair technique but is now being promoted also for new structures. Current generated by impressed anodes on the outside of the concrete and a positive electrical contact with the rebar stops the latter from rusting. The primary anode is usually brass or copper. 

The electrical conductivity and resistivity of concrete is indirectly related to the degree of resistance offered by concrete to the passage of corrosive species to the steel reinforcement The concrete resistivity is very high (>4KS2) and it can be best measured by the EIS technique (Electrochemical Impedance Spectroscopy) described earlier. ASTM Test C1202-94 can be used to determine concrete resistivity (Fig. 12.37). 

Electrochemical noise measurements. There may be skepticism about the application of electrochemical noise measurements to industrial rebar corrosion monitoring. Concerns about the perceived oversensitivity of the technique and fears of external signal interference have been raised. While such concerns may be justified in certain cases, electrochemical noise measurements have been performed with probes embedded in large concrete prisms (up to 4 m long). These... 

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