Reinforcing bars corrosion

Lempton, R. D. Jr., and Schemberger, D. 1996. Improving the Performance of Fusion-Bonded Epoxy Coated Steel Reinforcing Bars, CORROSION 96, Paper No. 323, NACE International, Conferences... 

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. 

Normally concrete is reinforced with plain carbon steel, but under conditions where rapid carbonation can occur or there is a risk of chloride contamination, corrosion-protected or more corrosion-resistant reinforcing steels may be necessary. Currently there are three reinforcing bars which have enhanced corrosion resistance ... 

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)... 

Finally, it is necessary to point out that although a particular method of corrosion control may be quite effective for the structure under consideration it can introduce unforeseen corrosion hazards elsewhere. Perhaps the best example is provided by cathodic protection in which stray currents (interaction) result in the corrosion of an adjacent unprotected structure or of steel-reinforcement bars embedded in concrete a further hazard is when the cathodically protected steel is fastened with high-strength steel bolts, since cathodic protection of the tatter could result in hydrogen absorption and hydrogen cracking. 

Typical uses include the production of non-dispersible underwater concrete and reduction of the accumulation of bleed water in mass concrete placed in deep forms. Consequently, AWAs are useful in mass concrete work because they prevent the formation of laitance on the surface of the concrete and thereby reduce the excessive cleaning between successive lifts. The admixtures also reduce the voids formed under horizontal reinforcing bars. Therefore, bond to steel increases and potential corrosion problems are reduced. The admixtures are also used in conjunction with WRAs in oil-well cementing grouts to reduce pipeline friction and rapid water loss and grouting of pre- and post-tensioned concrete ducts [47]. New valves and control devices under development in Europe and Japan used in conjunction with AWA will likely advance the field on underwater concrete. 

Virmani, Y.P., Clear, K.C. and Pasko, T.J. (1983). Time to Corrosion of Reinforced Steel in Concrete Slabs, Vol. 5, Calcium Nitrite Admixtures or Epoxy Coated Reinforced Bars as Corrosion Protective Systems, FHWA-RD-83-012, FHWA, US Department of Transportation, 71. 

Cathodic protection is one of the methods to mitigate the corrosion of steel in concrete Figure 7.24. Some factors to be considered in this connection are remaining service life of the structure should be more than lOyr delamination and spalls should be less than 50% by weight of concrete half-cell potential should be less than —200 mV (indicating breakdown of passive film) the structure should be sound the reinforcing bars should be electrically continuous AC power should be available. 

Corrosion Evaluation of Epoxy-coated Metallic-clad and Solid Metallic Reinforcing Bars in Concrete, US Department of Transportation, Federal Highway Administration, Publication FHWA-RD-98-153, December 1998. 

Smith, F.N., C.P. Cutler, D.J. Cochrane, Stainless Steel Reinforcing Bars, Proceedings, Conference on Understanding Corrosion Mechanisms in Concrete, Massachusetts Institute of Technology, Cambridge, MA, July 1997. 

Concrete is a highly alkaline environment because of the high concentration of calcium oxide or calcium hydroxide. The pH is greater than 12, which protects the steel-reinforcing bars used in the building from corrosion. Carbonation occurs when carbon dioxide reacts with the calcium carbonate and the pH of the environment drops to around 9. In this situation, carbonation becomes rapid, especially in industrialised areas and towns where there is a lot of exhaust emission from traffic. Acrylic coatings have become a versatile choice to overcome the problem of carbonation. 

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. 

Corrosive attack of an aggressive medium on composite polymeric materials is manifested as a change in its structure and properties without disruption of integrity or with destruction of the materials. The corrosion environment penetrates between macromolecules through micropores and fine capillaries and irreversibly changes the chemical structure of the composite and reinforcing bars or libers as well. Such changes of RubCon structure are characterized by formation of new active... 

The degradation of reinforced concrete in buildings is commonly caused by the corrosion of the steel reinforcing bars within the concrete, rather than by the loss of the mechanical properties of concrete. 

The extent of aqueous corrosion often depends on the presence of impurities and trace contaminants in the water present. For example, carbon-steel reinforcing bars in concrete corrode more severely in acidic conditions and in the presence of chloride ions, a process called electrochemical attack. On the... 

Before discussing corrosion-resistant reinforcement, mention will be made of the requirements for reinforcing bars and the characteristics of normal carbon-steel reinforcement... 

Epoxy coating of reinforcing bars is a protective technique developed in the 1970s in North America. Laboratory results confirmed the effectiveness of the epoxy-coated bars, in many cases, in preventing corrosion of reinforcement in carbonated or chloride-contaminated concrete [46]. Recently, however, doubts have arisen about their long-term durability in very aggressive environments, doubts borne out above all by negative experience reported on structures in tropical environments [47-49]. 

D. McDonald, D. Pfeifer, P. Virmani, Corrosion resistant reinforcing bars - findings of a 5-year study , Int. Conf on Corrosion and Rehabilitation of Reinforced Concrete Structures, Federal Highway Administration, Orlando, 7-11 December 1998 (CD ROM). 

C. Andrade, V. Feliu, Corrosion of reinforcing bars in carbonated concrete , British Corrosion Journal, 1980, 15, 135. 

Linear polarization resistance (LPR). These measurements allow the actual corrosion rate of embedded probes or of the reinforcing bars to be monitored over time. The measurement principle is described in Section 16.2.3. In addition to the reference electrode a counter-electrode of a corrosion resistant material (e. g. stainless steel or activated titanium) has to be embedded. Several compact LPR sensor systems were developed and installed in structures such as precast deck elements in a road tunnel [6,20]. When existing structures have to be monitored for corrosion rate, a corroding piece of rebar can be isolated (by cutting) to get... 

Latex-modified mortar and concrete have an excellent water impermeability as described in Sec. 2.4. Such good water impermeability also provides the high resistance of the latex-modified mortar and concrete to chloride ion (O ) penetration, which is one of the most important factors affecting the corrosion of reinforcing bars in reinforced concrete structures. Table gives the apparent chloride ion diffusion coefficient of latex-... 

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