Corrosion of Steel in Concrete

In a good quality concrete the reinforcing steel is protected against corrosion, because it is in cement paste covering of pH from 12.5 to 13.5, or at least 11.5. Steel is then covered by a passive film of the thickness from 1 to 100 run, composed of 

The corrosion of reinforcement is discussed in details in a book by Gizegorz Wieczorek, Concrete corrosion initiated by ehlorides or carbonation of concrete cover , Editor Dolno skie Wydawnictwo Edukacyjne, Wroclaw 2002. (in Polish). 

However, concrete is exposed to the action of external factors, primarily of CO2, SO2, chloride and sulphate solutions which causes pH decrease below 11. The analysis of the influence of pH changes on the durability of reinforcement in concrete can be done based on the equilibrium system elaborated by Pouibaix [341] for iron (Fig. 6.81). This is a diagram in the coordinate system pH— potential of metal, in relation to its salts. The thin, horizontal line represents the potential of semi-cell Fe Fe, which is independent of pH of solution. 

Three areas relating to the various state of iron can be distinguish on this Fe-H20 diagram the first one (1) in which iron is inert, and cannot be corroded (Fe), the second one (II) corresponding to the formation of Fe = FeOOH it means that the corrosion of iron occurs, and the third one (III) in which iron became covered with (straight line 1) or Fe203 (straight line 2) i.e. became passive and corrosion process does not occur. 

Conclusion from this diagram is that in the case of pH 13, typical for concrete, iron is in equilibrium with FCjO or Fe203, at a potential of -900 mV below this value corrosion does not occur. At higher potential the oxides, FCjO or Fe203 are formed and the passive film on reinforcement is thus produced, effectively decreasing the rate of corrosion, which became negligible low. 

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Forschungsprojekt I02D der EG im BRITE-Forschungsprogramm Electrochemi-cally Based Techniques for Assessing and Preventing Corrosion of Steel in Concrete, Bericht erhaltlich 1990. 

McKenzie, S. G., Techniques for Monitoring Corrosion of Steel In Concrete , Seminar Corrosion In Concrete-Monitoring, Surveying and Control by Cathodic. Protection , Global Corrosion Consultants, Telford (1986)... 

Although molybdate compounds have been advocated for corrosion inhibition purposes they have not been used as inhibitors in concrete practice. Experiments to ascertain the synergistic effect of a calcium-nitrite- sodium-molybdate combination (4.5 parts to 1 part) on corrosion of steel in concrete [64] showed that at the inhibitor-chloride ratio of 1 11 the combined admixture protected steel from corrosion and that it was more effective than when calcium nitrite was used alone. 

Cathodic protection is one of the methods to mitigate the corrosion of steel in concrete Figure 7.24. Some factors to be considered in this connection are remaining service life of the structure should be more than lOyr delamination and spalls should be less than 50% by weight of concrete half-cell potential should be less than —200 mV (indicating breakdown of passive film) the structure should be sound the reinforcing bars should be electrically continuous AC power should be available. 

The corrosion of steel in concrete is an electrochemical process. Due to local compositional or structural variations, some areas become positively and others negatively charged, and electrical cells are set up. The anodic reaction and the principal cathodic reaction are respectively typified by the equations... 

G. Sergi, Corrosion of Steel in Concrete Cement Matrix Variables, PhD Thesis, University of Aston,... 

Figure 4.4 Examples of consequences of corrosion of steel in concrete a) cracking of column and cross beam b) spalling and delamination of the concrete cover c) reduction of...

K. Tuutti, Corrosion of Steel in Concrete, Swedish foundation for concrete research, Stockholm, 1982. 

T. K. H. Al-Kadhimi, P. Banfill, S.G. Millard, ). H. Bungey, An accelerated carbonation procedure for studies on concrete , Advances in Cement Research, 1996, 8 (30), 47-59. C. L. Page, Nature and properties of concrete in relation to reinforcement corrosion , in Corrosion of Steel in Concrete, Aachen, 17-19 February 1992. 

G. K. Glass, N. R. Buenfeld, Chloride threshold level for corrosion of steel in concrete . Corrosion Science, 1997, 39, 1001-1013. 

Figure 7.1 Electrochemical mechanism of corrosion of steel in concrete [5]...

L. Bertolini, M. Carsana, P. Pedeferri, Influence of Stray Currents on Corrosion of Steel in Concrete , Int. (H Conf. Eurocorr/01, European Federation of Corrosion, Riva del Garda,... 

Laboratory study and calculations on the influence of crack width on chloride-induced corrosion of steel in concrete , ACI Materials Journal, 1997, 94, 56-62. 

B. Elsener, H. Bohni, Potential mapping and corrosion of steel in concrete , in Corrosion Rates of Steel in Concrete, ASTM STP 1065, N. S. Berke, V. Chaker, D. Whiting (Eds.), American Society for Testing and Materials, Philadelphia, 143-156, 1990. 

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

B. Elsener, Corrosion of steel in concrete , in Corrosion and Environmental Degradation, Vol. 2, Materials Science and Technology Series, )ohn Wiley, 389-436, 2000. 

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