ABSTRACT
In recent years the use of sacrificial anodes for cathodic protection in reinforced concrete structures has increased reflecting ease of installation, low maintenance requirements as well as desirability in prestressed concrete structures where the naturally controlled protection potential decreases the risk of hydrogen embrittlement.
Zinc-based alloys have been among the most evaluated galvanic materials for concrete structures, especially in USA, in many applications: thermal spray, superficial metal/mesh with and without hydrogel adhesive, embedded in concrete (point anodes) with or without salt activator, etc. However, the protection capacity lifetime of zinc alloys as used has been questioned based both on laboratory and on field application studies. Aluminum alloys have also been evaluated, showing sometimes better results as anode materials than zinc alloys. However, both zinc and aluminum alloy anodes may experience limited applicability in concrete structures exposed only to atmospheric conditions, as opposed to those in immersed, tidal and splash zone service.
This paper presents a review of the research work in the literature to date for both laboratory and field evaluations, toward identifying technically relevant situations where the use of sacrificial anodes may or may not be a practical option for reinforcement protection in concrete structures.
INTRODUCTION
Numerous reinforced concrete structures such as bridges and offshore platforms are exposed worldwide to aggressive chloride environments, and show evidence of corrosion after short service periods. The US Department of Transportation estimates yearly expenditures of approximately $30 million to $50 million to repair damage related to corrosion of coastal bridges. For this reason, much research effort since the mid 1970's has addressed various techniques to prevent that form of corrosion. Nevertheless, many existing structures have already a considerable amount of corrosion in progress. There is general consensus1 that the only assured way to arrest this process is by means of cathodic protection (CP) systems. Furthermore, CP may often be installed at a relatively low price compared to the alternative of repairing corroded structures. By the end of the 80's, the typical cost for impressed CP installations has decreased from about $75/m2 to $86/m2 of concrete in the 1980's to about $43/m2 in recent years. This decrease reflects the technology becoming increasingly simpler and contractors becoming more familiar and efficient with design and system installation. In North America,2 CP systems have been installed in more than 500 bridges, enabling complete systems to be developed in any place at a smaller price than in the past. CP systems are increasingly being considered too as a means to prevent corrosion processes from initiating.
