Abstract
Corrosion of reinforcing steel in concrete is a very serious and significant problem in the construction industry. The primary cause of corrosion of reinforcing steel is chloride attack or carbonation. Among several protection measures for concrete corrosion, the usage of corrosion inhibitors is very attractive from the view of cost and ease of application. Though there are numerous organic and inorganic compounds that have been tested and applied industrially as corrosion inhibitors, restrictive environmental regulations have compelled and motivated researchers towards the development of cheap, non-toxic and environmentally benign natural or green corrosion inhibitors. Recent studies on green inhibitors have shown that they are more effective and highly environmentally benign compared to synthetic inhibitors used in the industries. This chapter contributes to developing awareness, understanding and innovative involvement of materials and engineering students in this area that is vital to reduce expenditure related to corrosion problems when they serve in the industries.
TopBackground
In general, corrosion does not damage the concrete structures. The reason is that the pores in concrete contain high levels of calcium, sodium, and potassium hydroxide, which maintain a pH between 12 and 13. This high level of alkalinity passivates the steel inside the concrete, forming a dense gamma ferric oxide (γ–Fe2O3.H2O) that is self-maintaining which prevents rapid corrosion. But, since concrete is porous, both moisture and oxygen can easily penetrate through the pores and micro cracks in the concrete which subsequently create the basic requirements for corrosion of reinforcing steels.
Corrosion issues on reinforcing steel in concrete have significance in both structural integrity and in economic aspects. Corrosion can cause potholes, spalls, and delamination of reinforced highway structures such as bridge decks. Parking garages and support pillars also face damage because automobiles carry salt-bearing snow and ice through the garages, which melt further and permit aggressive chloride ions to permeate through the concrete. Similarly, coastal structures are subjected to corrosion when exposed to seawater containing high amounts of chloride.
A survey in the United States revealed that the cost of damage due to deicing salts alone is estimated between $325 to $1,000 million / year for reinforced concrete bridges and car parks. In North Africa, near coastal zones, and in the Middle East Arabian Gulf area, a few buildings were completely destroyed due to deterioration of the structures as a result of corrosion of reinforced concrete (El – Reedy, 2008). The cost can be considerably reduced by mitigating the corrosion problems of existing structures. It is estimated that $450–550 million could be saved per year by combating and solving the corrosion problems (Sastri, 2011). Furthermore, corrosion accidents may cause loss of human lives which cannot be estimated in monetary value.
Hence, it is very important to know and understand the concrete parameters, causes of corrosion, and the environmental exposure conditions. Numerous researches are proceeding for these purposes and focusing more towards finding the effective corrosion protection for concrete structures. Some of the protection methods include epoxy–coated reinforcement, improved quality of concrete cover, galvanized steel and corrosion inhibitors.
Key Terms in this Chapter
Stray Current: A current flowing through paths other than the intended circuit.
Electrolyte: A chemical substance/mixture containing ions that migrate in an electric field.
Corrosion Potential: The potential of a corroding surface in an electrolyte with respect to the reference electrode.
Reference Electrode: An electrode with an open circuit potential that is constant under similar conditions of measurement.
Corrosion Inhibitors: A substance when added in small concentrations to a liquid / gas, decreases the corrosion rate of metal/material.
Cell: An electrochemical system consisting of an electrolyte in which an anode and a cathode are immersed.
Corrosion: Deterioration of metal and/or material by chemical interaction with the environment.
Green Inhibitors: A non–toxic substance which is eco – friendly and biocompatible.
Reinforced Concrete: A composite material in which concrete’s tensile strength and ductility are enhanced by inclusion of steel reinforcement.
Passivation: A reduction of the anodic reaction rate of an electrode involved in corrosion.