Concrete, corrosion

Durability of concrete is defined as an ability to ensure, with required factor of safety and for assumed period of time, the functions predicted in the design of concrete structure. There is no need to explain that the durability has a capital practical meaning. Therefore munerous works were focused on the mechanism of concrete deterioration henee this knowledge is a starting point toward the invention of methods aimed in prevention or retardation of the durability threatening processes. 

Durability of concrete can be attained first of all by producing material of low permeability, which causes the migration of aggressive solution into this composite very difficult. The tightness of concrete will be the result of low porosity, whieh can be assured by low w/c ratio it should be generally lower than 0.4. That is why the high performance concretes are produced in majority with w/c of about 0.35. In case 

A very good relationship is obtained between the porosity, from mercury poro-simetry measurements, and permeability of hardened pastes. However, this method caimot be recommended in the case of concretes, as it has been mentioned in Chap. 5. A representative concrete sample cannot be satisfactorily reduced to the small specimen for mercury porosimetiy measurements. Therefore different methods of concrete enrichment in paste component are used the last one being the concrete porosity controlling factor. The concretes with lightweight aggregate are an exception in this case. There is usually too much paste in these small samples of concrete and the methods of concrete enrichment in paste worsen additionally the situation. 

In the opinion of experts, expressed during the workshop on the sulphate corrosion resistance, a low permeability of concrete is more important than the use of high sulphate resistant cement, in the case of sulphate corrosion hazard [65]. Therefore the w/c ratio maintained on a low level, together with higher cement content and proper curing of concrete at the early age of hardening, are of basic significance. 

The internal and external concrete corrosion are distinguish. The internal concrete corrosion results from the concrete components themselves, first of all the 

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Biczok, Concrete Corrosion and Concrete Protection, Chemical Publishing Co., Inc., New York, 1967. 

The transformation and transport rates that are involved in the sulfur cycle shown in Figure 4.4 determine to what extent the relevant components will exist in the different phases of the sewer system. As already shown — and further focused on when dealing with the concrete corrosion in Section 6.2.6 — the... 

Concrete corrosion is associated with the formation of hydrogen sulfide. Hydrogen sulfide-induced concrete corrosion has been a well-known major consequence of anaerobic conditions in sewers for many years (Parker, 1945a, 1945b, 1951 Fjerdingstad, 1969 Thistlethwayte, 1972 USEPA, 1974). Concrete corrosion is still a worldwide phenomenon that has great economic impact (Vincke et al., 2000). 

As long as sulfide remains in the water phase, no harmful effect will occur. The concrete corrosion problem is caused by hydrogen sulfide that from the gas phase is absorbed in the liquid film that exists on moist concrete surfaces in the... 

FIGURE 6.5. Principle of concrete corrosion in a sewer pipe. 

For systems where the formation rate of sulfuric acid is low, k is approaching 1. Where this formation rate is high, k may be about 0.3-0.4. In cases of severe concrete corrosion, a corrosion rate of 4-5 mm y-1 may be observed (Mori et al., 1991). 

A reliable concrete corrosion rate is difficult to predict. As already mentioned and also shown in Figure 4.4, it requires that several process and exchange rates in terms of primarily sulfide formation, emission to the sewer atmosphere, sulfide absorption and sulfide oxidation on the sewer walls can be determined. 

There are several examples from the literature that show that corrosion has seriously (and often quickly) deteriorated sewer networks (EWPCA, 1982 Aldred and Eagles, 1982 ASCE, 1989). Although corrosion is difficult to predict, the number of examples and extent of the problems observed have given a comprehensive knowledge of where and when concrete corrosion may exist. This knowledge can briefly be summarized as follows. 

A concrete corrosion rate is typically relatively low at circumstances with both moderate temperatures (< 209C) and relatively low sulfide concentrations in the wastewater (< 0.5 gS m-3). The following may increase the risk for corrosion ... 

Sand, W. (1987), Importance of hydrogen sulfide, thiosulfate and methylmercaptan for growth of thiobacilli during simulation of concrete corrosion, Applied and Environmental Microbiology, 53(7), 1645-1648. 

Griffin, D.F. (1975). Corrosion Inhibitors for Reinforced Concrete, Corrosion of Metals in Concrete, ACI SP-49, American Concrete Institute, Detroit, 95-102. 

Berke, N.S. (1989). Corrosion Inhibitors in Concrete, Corrosion 89, Paper no. 445, National Association of Corrosion Engineers, Houston, XX. 

R. Myrdal, Phenomena that disturb the measurement of potentials in concrete , Corrosion 96, Paper No. 339, NACE, Houston, TX, USA, 1996. 

P. Castro, A. A. Sagues, E. I. Moreno, L. Maldonado and J. Genesca, Characterization of activated titanium solid reference electrodes for corrosion testing of steel in concrete , Corrosion, 52(8), 1996, pp 609-617. 

Sulfur-oxidising bacteria convert inorganic sulfur compounds to sulfuric acid that can cause severe damage to mineral material. Thiobacillus species have been implicated with concrete corrosion in the Melbourne and Hamburg sewer systems due to sulfuric acid formation. However, a role in stone decay is less certain since sulfuric acid and calcium sulfate in stone can originate from the direct action of atmospheric pollution and acid rain. 

R. B. Polder, Cathodic protection of concrete ground floor elements with mixed in chloride , in Corrosion of Reinforcement in Concrete, Corrosion Mechanisms and Corrosion Protection, Papers from Eurocorr 99, J. Mietz,... 

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

S. Fiore, R. B. Polder, R. Cigna, Evaluation of the concrete corrosivity by means of resistivity measurements , Proc. Fourth Int. Symp. on Corrosion of Reinforcement in Concrete Construction, C. L. Page, P. B. Bamforth, J. W. Figg (Eds.), Society of Chemical Industry, Cambridge, UK, 1-4 July, 273-282, 1996. 

G. Sergi, S. E. Lattey, C. L. Page, Influence of surface treatments on corrosion rates of steel in carbonated concrete . Corrosion of Reinforcement in Concrete, C. L. Page, K. Treadaway, P. Bamforth (Eds.), Elsevier, 409-419, 1990. 

E. Maahn, B. Seirensen, The influence of microstructure on the corrosion properties of hot-dip galvanized reinforcement in concrete , Corrosion, 1986, 42, 187-196. 

K. C. Gear, Y. P. Virmani, Corrosion of non-specification epoxy coated rebars in salty concrete , Corrosion/83, NACE, Houston, Paper No. 114, 1983. 

P. Rodriguez, Effects of moisture availability on corrosion kinetics of steel embedded in concrete . Corrosion, 1993, 49, 1004-1010. 

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