Background

This article summarises the international development of cathodic protection of steel in concrete. The technology was developed in Europe and the USA for applications to buried prestressed concrete water pipelines (Refs. 1 & 2) and in California to deal with deicing salt attack of reinforced concrete bridge decks, and has been widely applied throughout North America for that purpose. It has been used and further developed in the UK to deal with a variety of problems ranging from buildings with cast in chlorides to bridge substructures contaminated with deicing salts and to marine structures and tunnels. It is also widely used on buildings and car parks in UK and Northern Europe. In the Middle East, severe corrosion problems caused by high levels of salinity in soils as well as marine conditions have lead to many large projects being carried out. It has also been used extensively in the Far East including Australia, Japan and Hong Kong.
North America

The USA, Canada and The Netherlands share the distinction among major Organisation of Economic Co-operation and Development (OECD) countries of not requiring the application of waterproofing membranes on major highway bridges although they apply deicing salts in the winter. This has lead to severe corrosion damage on US and Canadian Highway bridges. In 1955 the US Transportation Research Board found that concrete deterioration was rated fourth in a survey of major maintenance problems on bridges. By 1960 it was coming to the fore. The cost of corrosion induced repairs on bridges alone in the USA was estimated at US$20 billion in 1992 (Ref. 3).
Cathodic Protection

In 1959 Richard Stratfull of California Department of Transportation (Caltrans) reported that he had installed an experimental cathodic protection (CP) system on a bridge support beam (Ref. 4). Later he reported that, in 1972, he had installed a more advanced system on a bridge deck. (Ref. 5) The anode system was based on a conventional impressed current CP system for pipelines, but “spread out’ over a bridge deck. The conventional pipeline system was corrosion resistant silicon iron “primary” anode in a backfill of conductive carbon coke breeze.

Stratfull modified this by adding the coke breeze to asphalt. He applied silicon iron anodes at l2ft (3.66m) centres on the concrete bridge deck and then overlaid the anodes with a 3 inch (76mm) conductive asphalt wearing course. That system was energised in 1972 and operated for over 20 years. When surveyed in 1983 the system was working well even though some cracks and delaminations had been repaired before the cathodic protection system installation with insulating polymers that prevented current flow to all areas. Two similar systems installed in the mid 1970s are believed to be still operating.

One of the problems with this particular CP anode system was that US bridge decks were not originally designed for overlays. There was a requirement for an anode that did not change the profile of the bridge and did not increase the deadload. A slotted anode system was developed which put anodes into slots cut into the deck. The most successful deck anodes are now titanium based with mixed metal oxide coatings, either as ribbon in slots or as mesh under an overlay. The anode is supplied in various configurations, principally expanded mesh or strips. These systems are widely applied to bridge and car park decks.
Conductive Organic Coatings

Meanwhile the corrosion problem had been progressing from bridge decks to bridge substructures. Early experiments with conductive organic coatings showed the importance of optimum formulation and application conditions. Similarly, work with activated titanium mesh anodes in sprayed concrete overlays emphasised the requirements for quality of work in respect of preparation of the concrete surface and application of overlays.
Thermally Sprayed Zinc Coatings

Caltrans came to the fore again by developing thermal sprayed zinc applied to bridge substructures. This system was somewhat more durable than conductive coatings, without the requirement for a perfectly dry surface. The use of arc sprayed zinc on the 10,000m2 substructure of the Yaquina Bay bridge in Oregon in 1992 is one of the largest single substructure CP projects undertaken in the USA. It is still operating satisfactorily in 2001.

The Strategic Highway Research Program (SHRP) undertook an extensive survey of the CP systems on North American bridges in 1988-89. They found 840,000m2 of concrete surface under cathodic protection on the US and Canadian interstate highway system. SHRP wrote a review of the survey (Ref. 6), a state of the art report (Ref. 7) and a manual of practice (Ref. 8) for impressed current cathodic protection.
Sacrificial Anodes

The most recent developments have been in the evolution of galvanic or sacrificial anode systems. In the late 1970s experiments were carried out on bridge decks. Some were more successful than others, but none were seriously pursued. However, when corrosion was found on five bridge substructures in the Florida Keys, Florida DoT decided to experiment with arc sprayed zinc and several clamp on zinc systems (Ref. 9). These have been widely used in Florida. Of the 100,000m2 of thermal sprayed zinc systems in the USA, approximately 50% are galvanic systems in marine environments (see CPA Monograph No. 6, Ref. 10).

In Canada, the use of conductive organic coating anode systems on car parks (particularly deck soffits) is very widespread, particularly to private car parks attached to apartment buildings. There is a significant quantity of mesh and other anode systems applied to bridges and other structures. The original Caltrans systems were still extensively used until the mid 1990s.

Present estimates are that over 1½ million square metres of cathodic protection systems have been applied to North American structures and buildings. The type of structure by approximate order of volume is:

· Bridge Decks

· Bridge Substructures

· Car Parking Structures

· Wharves etc.

· Buildings (particularly on the Florida Coast)

There is a recommended practice for cathodic protection published by the US National Association of Corrosion Engineers (Ref. 11), and a test method for embedded anodes (Ref. 12).
The United Kingdom

By 1984 in the UK there was increasing concern regarding the costs of repair and maintenance of buildings and highway structures arising from corrosion of reinforcement. Cathodic protection of steel in soils and waters had been a well established and scientifically well understood engineering discipline since the 1940’s to the extent that it was (and remains) mandatory for buried pipelines carrying dangerous products and for many offshore facilities.

Early work by the Transport Research Laboratory, Spencer & Partners, Taywood Engineering, Harwell and others indicated that the largely pragmatic practical application to reinforced concrete in North America did have fundamental merit and was worthy of scientific investigation, controlled trials and careful implementation. The most significant of this early work in UK was the TRL programme to determine the efficacy of cathodic protection applied to trial blocks and the DoT/G Maunsell & Partners field trial at Gravelly Hill (Spaghetti Junction). These involved cathodic protection of four motorway slip road support structures and the parallel monitoring of two similar structures which were similarly repaired but not provided with cathodic protection.

Since this pioneering work in 1985 the UK market for reinforced concrete repair projects involving cathodic protection has grown from a spend of some £100,000 per annum to an estimated £20m per annum in 1993/94. Some 200,000m2 of cathodic protection has been applied to date in the UK according to the CPA database. Over 500 crossheads have been protected on the Midland Links motorway system alone.

UK industry and research has been significant in its contribution to effective pre-standards (Concrete Society/Icorr Technical Reports 36 & 37, Refs. 13 & 14), leading to the recently published European Standard EN12696:2000 (Ref. 15). The CPA is also working with the National Highways Authorities in England, Scotland, Wales and Northern Ireland on a Bridge Advice Note for Cathodic Protection of Highway Bridges. A full selection and range of cathodic protection systems and services is now available from UK members of the CPA.

A recent innovation in the UK has been the application of cathodic protection to steel framed masonry clad early 20th century buildings and structures. Over ten such structures have had cathodic protection applied in the last decade. These range from small gate structures to a Grade A listed government office building in Scotland with over 80 separate cathodic protection zones.
Continental Europe
Denmark

Northern Europe has seen cathodic protection applied to a significant number of structures. Denmark has two manufacturers of the control and monitoring systems used for CP of reinforced concrete structures, one of which also supplies anodes too. It is therefore not surprising that Denmark leads the field with over 60 installations with considerable activity in other Nordic countries. At present, activity is centred on swimming pools in Denmark with new installations being commissioned at a rate of about 8-10 a year; the anodes being installed in the pool walls. Other applications are car parks and bridge supports.
Norway

Norway also has an indigenous supplier and installer of a proprietary conductive coating anode system, primarily for use on car parks and buildings. Norway is mostly using CP on wharves, bridges and car parks with a few swimming pools. About 10 car park projects have been completed in the last few years. Conductive coating based CP systems have also been in use on four coastal bridges over the last 8 years. Remedial work is continuously going on to control corrosion of reinforcement on chloride contaminated balconies. To date many balconies have been treated successfully.
The Netherlands

In a recent paper it was estimated that about 20 structures in the Netherlands have been subjected to cathodic protection over the past 10 years (Ref. 16). These were predominantly buildings with cast in chlorides. Several had prestressed elements in them. Galvanic cathodic protection using a zinc sheet with a conductive hydrogel adhesive has also been used on precast concrete beams in housing projects (Ref. 10).
Switzerland and Italy

In Switzerland a number of tunnels and bridges have had cathodic protection applied. It is estimated that over 10,000m2 of cathodic protection had been applied up to 1997 (Ref. 17). Italy has used cathodic protection rather differently. It has applied over 150,000m2 of cathodic protection to new decks on autostrade bridges as a preventative technique. In many cases the bridges contained prestressed elements. Much of this work was done between 1990 and 1993.

There is a strong expectation that the publication of the European Standard on cathodic protection for steel in concrete (Ref. 15) will lead to wider application of CP as local and national governments will be provided with the tools to specify cathodic protection where appropriate.
The Middle East

In the Middle East, the prevalence of salt in the soil, air, water and cast into concrete means that up to 74% of reinforced concrete structures show significant corrosion damage after as little as ten to fifteen years (Ref. 18). Many structures have to be rebuilt every ten years or so unless extensive rehabilitation or repair is carried out. Cathodic protection has been used on a number of large marine structures as well as buildings, and industrial plants in Saudi Arabia, Kuwait, Oman, Dubai, the United Arab Emirates and elsewhere. The total area of anode exceeds half a million square metres, and may be as high as a million square metres.
The Far East

Systems were installed in Australia and Hong Kong as early as 1996. There is cathodic protection on new and old sections of the supports surrounding the Sydney Opera House (Ref. 19). A number of bridges, wharves and other structures have received CP amounting to more than 50,000m2. In New Zealand the National War Memorial Carillon Tower has been cathodically protected along with a few jetties. Similarly Hong Kong, with its large coastal exposure has had extensive systems applied to wharves and bridges. There are also installations in South Korea, Singapore, and a large number of small experimental installations in Japan.