Reinforced concrete inhibitors

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

The inhibitors considered thus far are either liquids or solids dissolved in solvents. Other useful type of inhibitors are vapor-phase corrosion inhibitors. These are used to minimize corrosion in electronics, packaging, processing industries, reinforced concrete,... 

Use Corrosion inhibitor in lubricants and steel- reinforced concrete. 

In general, reinforced concrete has proved to be successful in terms of both structural performance and durabiHty if the design mles (Chapter 11) and concrete technology (Chapter 12) were adequately considered. Additional protection measures will only be necessary in very aggressive environments or when a very long service life is required. As outlined in Section 11.8, corrosion inhibitors, thus chemical compounds added as admixtures to the fresh concrete, are one possible way to improve the durabiHty of concrete structures. 

The use of corrosion inhibitors is of increasing interest as they are claimed to be useful in reinforced concrete not only as preventative measure for new structures (as addition to the mixing water) but also as surface-applied inhibitors for preventative and restorative purpose. Apphcation on the concrete surface could be a promising technique to protect existing structures from corrosion or increase the lifetime of structures that already show corrosion attack. 

In this chapter the types of inhibitors presently available and their effectiveness in reinforced-concrete stractures are outlined. For more detailed information the reader is referred to the state of the art report published recently by one of the authors [1]. 

From the point of view of the apphcation, corrosion inhibitors can be used as a preventative or as a curative measure to increase the service life of a reinforced concrete structure. In preventative apphcations inhibitors are used as admixtures to the fresh concrete (calcium nitrite, organic inhibitor blends) or appHed on the surface of hardened concrete (MFP, organic inhibitor blends), in which case the inhibitor has to penetrate the concrete cover to reach the steel surface. In curative appHca-tions inhibitors are applied on the surface of hardened concrete with the goal to reduce the corrosion rate of the rebars. In the following sections the two modes of action are presented. 

Only calcium nitrite, introduced more than thirty years ago, has a long and proven track record as a corrosion inhibitor for reinforced concrete [1,4]. MFP and alkano-lamine-based organic inhibitor blends are increasingly used but unfortunately most of the commercial apphcations lack rigorous control of the inhibitor effect. One of the very few comparative field tests on chloride-contaminated concrete studied MFP and a proprietary alkanolamine inhibitor added in the side-walls of a tunnel (16). The inhibitors were applied by the producers. The measurements of macrocell currents and half-cell potential mapping revealed that both inhibitors were virtually ineffective at the chloride concentrations of 1-2 % by mass of cement present [16]. 

Assuming that the inhibitor action in laboratory experiments has been established, there remain two critical points for a successful and reliable application on reinforced concrete structures ... 

The use of corrosion inhibitors could be a promising technique in restoring reinforced concrete structures, offering benefits as reduced costs and inconvenience of repairs. It has, however, to be taken into account that the use of corrosion inhibitors in repair systems is far less well-established than their application as admixtures in new structures. The performance of proprietary corrosion inhibitors in repair systems marketed under different trade names is not yet sufficiently documented by independent research work, especially when considering field tests. 

B. Elsener, M. Btirchler, F. Stalder, H. Bohni, "A migrating corrosion inhibitor blend for reinforced concrete - Part 2 Inhibitor as repair strategy , Corrosion, 2000, 56, 121. 

J. Tritthart, "Transport of corrosion inhibitors in concrete , Proc. COST 521 Workshop Corrosion of Steel in Reinforced Concrete Structures, 28-31 August 2000, T. D. Sloan, P. A. M. Basheer (Eds.), The Queens University, Belfast, 289-300, 2000. 

Broomfield, J.P. (2000). Results of Long Term Monitoring of Corrosion Inhibitors Applied to Corroding Reinforced Concrete Structures. Corrosion 2000. Paper No. 791. 

Broomfield (2000) carried out regular surveys using LPR (see Section 4.12) on some reinforced concrete support pillars which had calcium chloride cast in as a set accelerator. These had been repaired with vapour phase corrosion inhibitors applied. Measurements from 1995 to 1999 showed the increase in the corrosion rate in treated and untreated control areas, with the corrosion rate peaking at around 0.5 to 1.0 A/cm (5-10 mm per year) with cracking seen approximately one year later. This demonstrated that the inhibitor applied with the chloride content of the structures was too high to stop corrosion. It also showed that a factor of two difference in corrosion rate between treated and untreated area made no significant difference to the rate and extent of cracking. 

Sprinkel, M. and Ozyildirim, C. (1998). Evaluation of Exposure Slabs Repaired with Corrosion Inhibitors. Proc. International Conference on Corrosion and Rehabilitation of Reinforced Concrete Structures, Orlando Elorida. 

Uses Corrosion inhibitor reinforced concrete Manuf./Distrib. Varsal Instruments http //www.varsal.com... 

The interactions between reinforced concrete, prestressed concrete and the marine environment are very complex. From the corrosion standpoint, the primary consideration is protection of the embedded steel from attack by the aggressive marine environment. This protection may rely solely on the ability of the ordinary concrete cover to protect the embedded steel or may be augmented by the addition of corrosion inhibitors to the concrete, by coating of the steel, by cathodic protection, or a combination of one or more of these methods. 

Elsener, B., Buchler, M., Stalder F. and Bdhni, H. (1999) Migrating Corrosion Inhibitor Blendfor Reinforced Concrete. Part 1 Prevention of Corrosion, Corrosion 55. 

Corrosion inhibitors. Corrosion-inhibiting admixtures are essentially designed to improve the performance of good-quality reinforced concrete. It has been emphasized that the function of such admixtures is not to make good concrete out of poor quality concrete. Adherence to this important principle is important in order to avoid unrealistic performance expectations for corrosion inhibitors in concrete. 

LA. Callander and F. Gianettl, "A review on the Use of Calcium Nitrite Corrosion Inhibitor to Improve the Durability of Reinforced Concrete", V. Corrosion Symposium, 1996,139-149. "Corrosion and Repair of Unbonded Single Strand Tendons," ACl/ASCE Committee Report 423, 4R-98, American Concrete Institute, 1998,20. 

Corrosion Inhibitors. Steel-reinforcing wire and rods embedded in concrete containing quinoline or quinoline chromate are less susceptible to corrosion (72) (see Corrosion and corrosion control). Treating the surface of metals with 8-hydroxyquinoline [148-24-3] makes them resistant to tarnishing and corrosion (73). Ethylene glycol-type antifreeze may contain quinoline, 2-chloro-, 4-amino-, 8-nitro-, or 8-hydroxyquinoline to prevent corrosion (74). 

Corrosion Inhibitors. Steel-reinforcing wire and rods embedded in concrete containing quinoline or quinoline chromate are less susceptible to... 

The cost of various techniques can only be given very roughly, and any estimate will be incomplete, since the actual cost will vary from one application to another. Furthermore, different types of prevention mechanisms are not directly comparable. Beyond this, it can be said that with respect to normal carbon-steel reinforcement, use of galvanized and epoxy-coated bars costs about twice as much, and the cost of stainless-steel reinforcement is about 5 to 10 times higher. The use of nitrite inhibitors in higher doses costs approximately 30 /m of concrete (volume). Coatings may vary from 7 to 50 /m of concrete surface, hydrophobic treatment costs about 10 /m. Cathodic prevention varies from 50 to 100 /m. ... 

The application of inhibitors on the concrete surface requires the transport of the substance to the rebar where it has to reach a sufficiently high concentration to protect the steel against corrosion or reduce the rate of the ongoing corrosion. In this context only corrosion inhibitors that prolong the service life due to chemical or electrochemical interaction with the reinforcement are considered. Any other substances that may prevent the onset of corrosion or reduce ongoing corrosion by other means, such as surface treatment (e. g. hydrophobation) or additions that reduce the porosity of the concrete (e. g. fly ash, silica fume, waterproofing admixtures, etc.), are not considered to be corrosion inhibitors and are treated in other chapters. 

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

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