Cathodic prevention (CPrev) of reinforced concrete structures is used to improve the corrosion resistance of reinforcement for marine structures that are expected to suffer from chloride-induced corrosion during their service life. As a part of a major rehabilitation programme to the Sydney Opera House during 1995-1996, a CPrev system was installed to the reinforced concrete pre-cast elements of the Western Underbroadwalk of the Sydney Opera House.
This paper will assess the cathodic prevention system performance after nearly 10 years of operation and will make a comparison between the designed and operating cathodic prevention current density of the system.
Cathodic Prevention (CPrev) is a proven electrochemical technique used in steel reinforced concrete structures to prevent the onset of corrosion caused by environmental chloride contamination. CPrev is used to improve the durability and service life of the structure and reduce maintenance costs in the long-term. It may be used with other compatible advances in concrete technology such as high performance concrete mixes, to further increase the durability of the structure in severe environments.
As a part of a major rehabilitation programme to the Sydney Opera House Under Broadwalk in 1995- 96, new reinforced concrete pre-cast sections were installed to replace sections that had deteriorated due to chloride-induced corrosion of the reinforcement. As part of these construction works a CPrev system was installed to these new precast elements, as they were at a very high risk of chloride contamination. Sections of the precast elements are in the dry atmospheric zone while other sections are subject to saltwater splashing at high tide each day and immersion at very high tides.
The CPrev system was installed to 18 pre-cast A-Frames, 17 mid span ties and 17 pre-cast walkway sections of various lengths.
The precast elements contain prestressing steel, and the avoidance of overprotection was a major consideration in the design and control of the system.
The CPrev system was installed in conjunction with a Cathodic Protection (CP) system to previously existing concrete elements that were retained in the underbroadwalk. The cathodic protection system shall not be discussed in this paper. However, a water immersed anode system installed to protect the immersed sections of existing piles has an effect on the precast elements at high tide, and this effect will be considered when discussing results.
Current standards on cathodic protection in concrete provide guidelines for expected operating current densities for cathodic prevention systems of 0.2 to 2mA/m2. One of the purposes of this paper is to assess the applicability of this guideline.
CATHODIC PREVENTION BACKGROUND
In the presence of chlorides, for example on bridge decks where de-icing salts are spread, or in splash zones of marine structures, additional preventive corrosion measures must be used to guarantee service life of even a few decades.
Cathodic prevention is one of these measures. Such a system was applied for the first time in Italy in 1989 as a method of preventive maintenance of new structures that are expected to become affected by chloride contamination in the future and to emphasize that the aims, operating conditions, throwing power, and effects (particularly those regarding hydrogen embrittlement) of CPrev, as well as many of the engineering and economic aspects of the design, construction, monitoring and maintenance of CPrev are different from those of normal cathodic protection, so the name of cathodic prevention was proposed.
