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Corrosion Special Topical Papers

Emerging Corrosion Control Technologies for Repair
 and Rehabilitation of Concrete Structures
*

Dr. Jianhai Qiu
School of Materials Engineering
Nanyang Technological University
Nanyang Avenue, Singapore 639797

1. Introduction                                                                                                     

Technology always advances faster than the development of codes, specifications, and standards. Recent innovations in materials, processes and corrosion control technologies have enabled designers and architects to meet performance-based specifications at lower life cycle cost. This paper focuses on the recent developments and applications of state-of-the-art emerging technologies for repair and rehabilitation of reinforced concrete structures. These technologies include: press-on zinc hydrogel anode CP system, snap-on zinc mesh anode CP system, pre-packaged zinc sacrificial anode system, conductive concrete, electrochemical chloride extraction (CE) or electrochemical chloride removal (ECR), electrochemical realkalisation (ER), duplex/stainless steels and alloys reinforcements. Most of these emerging technologies are also increasingly used for corrosion prevention in new concrete structures. Some application examples are also cited to demonstrate the potentials of these promising technologies in the new millennium.

2. Primer on Concrete Corrosion

2.1 General

Reinforced concrete is the most versatile and potentially one of the most durable materials that a designer can choose to build almost any type of structures. Under normal conditions, the reinforcing steel is in a passive state it is protected from corrosion by a rather inert oxide film (passive film) on its surface. The formation and the subsequent breakdown of such an oxide film are mainly determined by the pH and the chloride content of the concrete. When the local environment at the rebar/concrete interface cannot maintain the passive state of reinforcing steel, active corrosion in either uniform or localized form (pitting) will occur. Because of the widespread use of reinforced concrete, today corrosion of reinforcing steel is rapidly becoming a major problem throughout the world. Bridges, marine structures, buildings and other concrete structures are being severely damaged by corrosion.

2.2 Carbonation

Carbonation refers to the interaction of carbon dioxide in atmosphere with the hydroxides in the concrete. Carbonation is detrimental to the corrosion resistance of reinforcing steel as it destroys the passive film.

Ca(OH)2+CO2=CaCO3+H2O

CaCO3+CO2+H2O=Ca(HCO3)2
                                   soluble bicarbonate

Leaching of Ca(OH)2 due to carbonation causes the pH of the concrete to fall below 9 and this leads to the depassivation of the reinforcing steel surface.
 

 

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