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.
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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