Steel reinforcements in concrete

Considerable alterations have been made in the chapters concerned with technical applications which are the result of advances in electrochemical corrosion protection in general practice. Here also, abbreviation and omission of less relevant parts of the older editions have had to be made to create space for more recent information. Recent applications in the chemical industry have necessitated a complete rewriting of the industrial chapter. A new chapter is included on the cathodic protection of steel reinforcement in concrete. 

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. 

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. 

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. 

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. 

B. Malric, Preliminary testing of Na2P03p as a curative corrosion inhibitor for steel reinforcements in concrete. Cement and Concrete Research, 1992, 22, 869. 

A. E. Bauer, D. J. Cochrane, The Actual Implication of Stainless Steel Reinforcement in Concrete Structures,... 

C.A. Loto, Effect of inhibitors and admixed chloride on electrochemical corrosion behavior of nuld steel reinforcement in concrete in seawater. Corrosion 48 (1992) 159—163. 

Electrochemical monitoring methods have also been developed for application on steel reinforcement in concrete. These methods include potential measurement on the concrete surface, linear polarization (LPR) and determination of polarization curves [9.17]. Electrical resistance probes (ER) and probes embedded in the concrete for measuring galvanic current have also been used. 

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. 

ASTM G109-99a (2005a) Standard Test Method for Determining the Effects of Chemical Admixtures on the Corrosion of Embedded Steel Reinforcement in Concrete Exposed to Chloride Environments. American Society of Testing and Materials, West Conshohocken, PA. 

Bamforth, P. (1994). Admitting that chlorides are admitted . Concrete, 28(6) 18-21. Broomfield, J.P. (2004). Galvanized Steel Reinforcement A Consultant s Perspective, Chapter 9 in Yeomans (ed.). Galvanized Steel Reinforcement in Concrete. Publ. Elsevier, Oford UK, pp 276-279. 

Yeomans (ed.) (2004). Galvanized Steel Reinforcement in Concrete. Publ. Elseviei Oxford, UK. 

The diffusion of oxygen is of particular importance as the corrosion of steel reinforcement in concrete is regarded. Ludwig [157] was among the first authors who initiated the studies focused ou this problem. The linear relation between the permeability and oxygen diffusion rate was found, as presented in Fig. 5.72 [138]. It has been proved in the same experiments that the CO2 diffusion can be evaluated based on the oxygen diffusion coefficient. 

There are several methods that can be used to control corrosion of steel reinforcements in concrete. First, the design of the structure should provide for drainage of salt-containing waters away from the reinforced concrete. Second, concrete of adequate thickness, high quality, and low permeability should be specified to protect the reinforcements from the environment. Third, chloride content of the concrete mix should be kept to a minimum. For further protection, the steel reinforcements can be epoxy-coated. In many parts of North America, steel reinforcements used in bridge decks are now epoxy-coated as a standard construction procedure. Cathodic protection is also being used, both with impressed current anodes and with sacrificial anodes [61]. (See Chapter 13.)... 

Steel reinforcements in concrete, being passive, are noble in potential with respect to steel outside the concrete that is galvanically coupled to the reinforcements. The measured potential difference is in the order of 0.5 V [62]. The effect of large cathode area and small anode area has caused premature failures of buried steel pipe entering a concrete building [63]. In this situation, use of epoxy-coated reinforcements (to coat the cathode) or insulated couplings should prove beneficial. 

Effect of Heat Treatment 7.4 Steel Reinforcements in Concrete References General References Problems... 

With durable anodes, such as the DSA , current is applied from an external power supply to achieve cathodic protection. However, it is necessary to optimize the electrode geometry of this system to realize uniform current distribution. Cathodic protection is widely used to protect pipelines, buried steel structures, steel reinforcement in concrete, and chemical process equipment. 

Yeomans, S. R. (1991). Investigations of galvanized and epoxy coated steel reinforcement in concrete. I6th Int. Galv. Conf., EGGA, London, GBl/1-5. 

The pH of the electrolyte does not only have an effect on the passivation potential, but also on the passivation current density, because both the metal dissolution kinetics and the solubility of hydroxides depend on pH. Figure 6.16 shows that the passivation current density of iron becomes smaller at higher pH. This has been explained by a lowering of the solubility of ferrous hydroxide, which precipitates at the surface. Since both the passivation potential and the passivation current density decrease with increasing pH, spontaneous passivation of iron becomes possible in basic, aerated media. This explains why steel reinforcements in concrete (pH >13) resist corrosion well as long as chemical reactions with carbon dioxide from air (carbonation of concrete) do not modify the alkalinity. 

Carbon steels rust when they are in contact with humid air (Chap. 8) and therefore they are usually protected by a coating. In aqueous solutions, their corrosion rate depends on the pH (Figure 12.6). At low pH, proton reduction takes place and the corrosion rate becomes higher as the pH decreases. In neutral solution, oxygen transport controls the rate of corrosion, which therefore does not vary with pH. Finally, in an alkaline solution steel passivates and the corrosion rate decreases to very low values. This explains for example, why steel reinforcements in concrete do not deteriorate as long as the pH stays high (pH > 13) but may rust if the pH in the concrete drops to a lower value because of carbonation reactions of cement. 

The best environment in which to test rebars is concrete, and several test methods are available. A new ASTM test method, G 109, Test Method for Determining the Effects of Chemical Admixtures on the Corrosion of Embedded Steel Reinforcement in Concrete Exposed to Chloride Environments, was issued in 1992. This method uses relatively high water-to-cement (w/c) ratio concrete at a low concrete cover. Because these conditions are not representative of recommended field applications [23], this is a screening test method. 

Yeomans, S. R., "Aspects of the Characteristics and Use of Coated Steel Reinforcement in Concrete, Corrosion/93, Paper 329, NACE, New Orleans, March 1993. 

Standard Test Method for Determining the Effects of Chemical Admixtures on the Corrosion of Embedded Steel Reinforcement in Concrete... 

Potential measurements of steel reinforcement in concrete are relatively difficult and have been the subject of a interesting discussion carried out by Myrdal (1996). 

What is the basic objective of applying cathodic protection to steel reinforcement in concrete with particular reference to alkalinity How is this objective achieved ... 

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