Corrosion of concrete reinforcement

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,... 

The decision to cathodically protect reinforced concrete structures depends on technical and economic considerations. Cathodic protection is not an economic process for small area displacements of the concrete due to corrosion of the reinforcing steel arising from insufficient concrete covering. On the other hand, the... 

Corrosion of metal reinforcement bars has caused concrete to fall off the corners of cooling towers. 

Corrosion usually results in a leak or failure of a support because a vessel or support gets too thin. It is then not strong enough to withstand the pressure or load. However, rust can cause failure in another way. It occupies about seven times the volume of the steel from which it was formed. V/hen rust occurs between two plates that have been bolted or riveted together, a high pressure develops. This can force the plates apart or even break the bolts or rivets (see Section 9.1.2 g). Corrosion of the reinforcement bars in concrete can cause the concrete to crack and break away. 

Hayfield, P. C. S. and Warne, M. A., Titanium Based Mesh Anodes in the Cathodic Protection of Concrete Reinforcing Bars , presented at UK Corrosion, Brighton (1988)... 

Concrete exposed to deicer salts, or to a marine environment is subjected to chloride and sodium loading. The ability of concrete to resist the penetration of chlorides and sodium is a primary design consideration in marine or cold environments. The ingress of chlorides into concrete is a major problem due to chloride-induced corrosion of the reinforcing steel and deicer salt scaling [a process by which a thin layer (< 1 mm) of concrete deteriorates from the surface of the concrete]. The penetration of sodium from sea water or deicer salts is generally... 

The effect that accelerators have on the role of concrete in providing protection against the corrosion of steel reinforcement has been the subject of several investigations and considerable controversy. Many studies have shown that the factors below are relevant to the discussion ... 

R. Myrdal and K. Videm, Evaluation of corrosion of steel reinforcement in concrete from potential measurements of embedded reference electrodes , Corrosion 95, Paper No. 512, NACE, Houston,TX, USA, 1995. 

Chloride ions at concentrations greater than about 0.4% wt/wt, calculated on the weight of the concrete, results in the corrosion of the reinforcing bars ultimately, the surface of the concrete above the steel reinforcing rods breaks off. 

The water prodnced in the reaction between Ca(OH)2 and CO2 created another problem CO2 also reacts with water to form carbonic acid (H2CO3), and hydrogen ions produced by the acid promote the corrosion of the reinforcing iron bars in the concrete, thereby weakening its stmcture. This simation was dealt with effectively by painting all concrete surfaces with an impermeable coating. 

Sodium nitrite, sodium benzoate and sodium chromate have been used as admixtures, to inhibit corrosion of steel reinforcement in concrete. Although these chemicals have been shown to be effective in specific situations, there is little general data available on either their effectiveness or disadvantages. 

Each of the transport processes that leads to corrosion of the reinforcement and then governs its kinetics can be characterized by a parameter (D, S, K, p) that depends on the concrete properties and can be determined experimentally. Table 2.5 shows the parameters that are relevant to different situations. At least theoretically, these parameters can be used in the design of concrete structures to calculate the evolution in time of corrosion (initiation or propagation) or any other type of degradation as a function of concrete properties and environmental conditions. 

Protection that concrete offers to steel against stray current ceases when corrosion of the reinforcement has initiated, e. g. due to carbonation, chloride contamination, or the stray current itself In this case, any current flowing through the steel will increase the corrosion rate at the anodic site, similarly as in buried steel structures. Figure 9.8 shows that even small driving voltages can lead to an increase in the corrosion rate on the anodic area (from to Furthermore, it has been observed that if steel is subjected to pitting corrosion in chloride-contaminated concrete, the anodic current increases the size of the attacked area [5]. 

N. ). M. Wilkins, P. F. Lawrence, The corrosion of steel reinforcements in concrete immersed in seawater , Proc. Corrosion of Reinforcement in Concrete, (Ed.) A. P. Crane, Society of Chemical Industry, 1983, 119-141. 

This chapter deals with the strategies for repair of reinforced-concrete structures damaged by carbonation or chloride-induced corrosion of the reinforcement, and outlines the most common methods. Details of conventional repair and electrochemical maintenance methods are reported in Chapters 19 and 20. The repair of prestressed concrete structures is outside the scope of this book. 

Carbonation-induced corrosion. If carbonation has been identified as the cause of corrosion of steel reinforcement and other deterioration processes can be neglected, the evaluation of the depth of concrete to be removed can be carried out as shown in Figure 19.1. The present conchtion of the structure has to be expressed by means of ... 

Reinforced concrete bridges suffer from corrosion of the reinforcement and, consequently, concrete degradation because of the high tensile forces exerted by... 

L. Maldonado, Chloride threshold for corrosion of galvanized reinforcement in concrete exposed in the Mexican Caribbean, Mater. Corros. 60 (2009) 536—539. 

F. Tittarelh, G. Moriconi, Comparison between surfece and bulk hydrophobic treatment against corrosion of galvanized reinforcing steel in concrete, Cem. Concr. Res. 41 (2011) 609-614. 

The development and building of large concrete structures for offshore oil and gas production in the 1970s called for increased attention to corrosion of steel reinforcement, and of seawater-exposed steel parts in metallic contact with the reinforcement. Research projects were estabhshed at various laboratories, e.g. as dealt with in References [8.20, 8.21]. 

The corrosion of the reinforcing steel in concrete is a major problem facing civil engineers today as they maintain an ageing infrastructure. Potentially it is a very large market for those who develop the expertise to deal with the problem. It is also a major headache for those who are responsible for dealing with structures suffering from it. 

Wilkins, N.J.M. and Lawrence, P.E. (1980). Concrete in the Oceans Fundamental Mechanisms of Corrosion of Steel Reinforcements in Concrete immersed in Sea Watei Technical Report 6, CIRIA/UEG Cement and Concrete Association, Slough, UK. 

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