Corrosion 199 of concrete

Mori, T., M. Koga, Y. Hikosaka, T. Nonaka, F. Mishina, Y. Sakai, and J. Koizumi (1991), Microbial corrosion of concrete pipes, H2S production from sediments and determination of corrosion rate, Water Sci. Tech., 23(7-9), 1275-1282. 

Parker, C.D. (1945a), The corrosion of concrete 1. The isolation of a species of bacterium associated with the corrosion of concrete exposed to atmospheres containing hydrogen sulphides, Aust. J. Expt. Biol. Med. Sci, 23, 81-90. 

Parker, C.D. (1951), Mechanics of corrosion of concrete sewers by hydrogen sulfide, Sewage Ind. Wastes, 23, 1477-1485. 

Fig. 6.9 Weighted total corrosion of concrete with 2% calcium nitrite (NACE International, reprinted with permission).

Diercks, M., Sand, W. Bock, E. (1991). Microbial corrosion of concrete. Experientia,... 

The first of the previous reactions is responsible for a good portion of the acid rain problem troubling the industrialized world. Sulfur, present in small quantities as an impurity in coal and oil, is converted to sulfur dioxide when the coal or oil is burned then the sulfur dioxide reacts with the moisture in the air to produce sulfurous acid. Sulfurous acid can react with the oxygen in air to produce sulfuric acid. These acids are washed from the air by rain (or snow), and the solution can cause some corrosion of concrete and metal in buildings. Acids in the air and in the rain or snow also injure trees and other plants, as well as animals, including humans. In high concentrations, acids and acid anhydrides in the air can make breathing difficult, especially for people who are already in poor health. 

Corrosion of concrete by bacteria that oxidize sulfur compounds into sulfuric acid was reported by Parker (1945, 1947) and has been examined more recently by Fjerdingstad (1969). The lowest pH is tolerated by Thiobacillus concretivorus Parker (pH 2.75 + 0.42) and T. thiooxidans Waksman and Joffe (pH 2.35 0.32). Within 100 days of incubation in a T. thiooxidans culture, 60% of a 3.6 g block of concrete were dissolved. Bacterial destructive activity has also been established on buildings and monuments (Krum-... 

Parker, C.D., 1947. Species of sulphur bacteria associated with the corrosion of concrete. Nature, 159 439—441. 

The accumulation of salts within the concrete pore structure can also lead to the corrosion of reinforcing steel, the fourth form of deterioration identified above. This corrosion is accompanied by an increase in the volume of the steel, which eventually causes the concrete to crack and spall. In discussing the atmospheric corrosion of concrete reinforcements, Skoulikidis (21) notes "The increase of atmospheric pollution Intensifies the corrosion tendency of the reinforcements in the atmosphere. The cracking of the concrete was observed more frequently with an increase of the atmospheric pollution (SO2, CO2, NH3, NOx> etc.) and the acceleration of the corrosion by the formation of a more conductive environment, that also chemically attacks the metals."... 

Skoulikidis, T. N. Atmospheric Corrosion of Concrete Reinforcements and Their Protection. Date unknown,... 

Fig. 4.8. A schematic presentation of corrosion of concrete by a cooperation of 1, the sulfate-reducing bacteria and 2, the sulfur-oxidizing bacteria in sewerage systems. The surface of concrete dipped in sewage is not corroded...

In the corroded concrete, there also reside acidophilic iron-oxidizing bacteria (see below) besides the usual sulfur-oxidizing bacteria. The acidophilic iron-oxidizing bacteria show optimal growth pH at 2.0, and oxidize not only ferrous iron but also sulfur compounds. Therefore, they can participate in the corrosion of concrete. We have to consider the action of both the usual sulfur-oxidizing bacteria and the acidophilic iron-oxidizing bacteria when we exploit the compounds which inhibit the bacterial corrosion of concrete. 

Are there any methods to inhibit the growth of the bacteria participating in the corrosion of concrete A few compounds have been exploited which inhibit the growth of the sulfur-oxidizing and acidophilic iron-oxidizing bacteria. A reagent... 

The corrosion of concrete sewer pipe is not a direct result of the presence of hydrogen sulfide gas in the headspace above the water rather the primary mechanism of corrosion is caused by the presence of Thiobacillus bacteria, which reside on the invert of the pipe see Figure 10.7. This genus of bacteria has the ability to oxidize hydrogen sulfide gas to form sulfate, which results in the formation of sulfuric acid see reaction (10.11) ... 

Acid atmospheric waters can reduce the pH of surface waters with low neutralization capacity. For example, in Scandinavian lakes and rivers, acidification caused by acid atmospheric precipitations results in the killing of fish species, trout and salmon. Apart from the reduced abundance of fish, acid atmospheric waters also unfavourably affect the soil composition (soil becomes poor in cations, replaced by hydrogen ions), as well as the growth of plants. They also cause significant corrosion of concrete, mortar, iron and other metals. Because of this property, low mineralization and irregularity of precipitation, atmospheric waters are very seldom used directly for water supplies. In some cases atmospheric waters can be an important source of nitrogen compounds for agriculture. 

R. Javaherdashti, P.A. Farinha, P.K. Sarker, H. Nikraz. On microbial corrosion of concrete Causes, mechanisms and mitigation. Concrete in Australia, March 2006. 

The thermal treatment of concrete can cause the detrimental effect of delayed ettringite formation, resulting in the deterioration of concrete elements. The problem of delayed ettringite formation belongs to the internal corrosion of concrete and will be discussed in the chapter relating to this corrosion. 

Neither the duplex film, nor the oriented portlandite crystals in the interfacial zone were found by all the authors [19, 20]. However, there is a common opinion that this area is enriched with calcium hydroxide crystals and exhibits higher porosity. Consequently, it will have a great impact on the corrosion resistance of concrete. The transition zone of high porosity is the weakest micro-area where the corrosion of concrete will begin [21]. For this reason, the interfacial transition zone became a subject of numerous studies [16,17,22-28]. The constitution of this zone can be easily observed on the model proposed by Rooij et al. [28] (Fig. 6.9). 

The delayed ettringite formation is rated among the internal corrosion of concrete, which is induced by a heat treatment of concrete, and thus occurring mainly during the precast concrete elements production. However, one carmot exclude the temperature rise up to 70 °C in the interior of massive concrete stracture, as a consequence of heat evolution process in hardened cement paste, and in this condition ettringite can be unstable. 

There is a cormnon opinion that corrosion of concrete needs the liquid environment or at least an atmosphere of high hmnidity. The transport of liquid through the concrete causes the sequence of processes, includiug at first the concrete components of the highest reactivity calcium hydroxide and calcium aluminate hydrates. One can thus conclude that the phase composition of cement has a great impact on the behavior of concrete in any aggressive environment. 

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