Less demolition of old concrete and thus less disruption and waste? The reliable protection of the reinforcement in concrete structures while ensuring safety? TNO believes cathodic protection (CP) holds the solution to the problem of protecting concrete reinforcement during complex repairs.
Eventually, reinforcement in concrete will rust. Formally, this is known as an anodic corrosion reaction. Corrosion of reinforcement is an electrochemical process in which the dissolution of iron is coupled to a cathodic reaction, namely the conversion of water and oxygen. Conventional repair of concrete is only effective and durable if it is very thorough and penetrating: all concrete with too high a chloride level must be broken out. Next, the steel must be cleaned thoroughly and, finally, all open spots must be repaired. When CP is applied, only loose concrete is removed and repaired. Next, a conductor is applied to the surface of the concrete (or in holes drilled in the cross-section) and connected to the positive terminal of a power supply. The reinforcement is connected to the power supply's negative terminal. At a few Volts, a small current is generated. This suppresses corrosion due to the fact that on the steel surface only the cathodic reaction can occur.
In every repair project, whether conventional or CP, there must be a guarantee that the reinforcement will be protected. Afterwards, the structure should be safe and durable. Every repair project is different because every structure is unique in terms of its build up, ageing process and damage. While the work that must be carried out and the materials that are used are the same in every project, CP remains a tailor made operation. It involves design and engineering, power supplies and data loggers, anodic material (the quantity depends on the size of the surface to be protected), repair sites, scaffolding and traffic measures. CP increases the service life of a repaired structure considerably.
For 20 years now, TNO has been working on the development and application of CP. Over the years we have seen various technical innovations. Especially in the field of anodic materials and anodic systems. For example, in the 1990s titanium mesh in an overlay of shotcrete was first used in the Netherlands. The use of titanium anodes in drilled holes is another growing trend we are seeing. The recent expansion of CP can be attributed to the use of conductive coatings. These are easy to apply, light, easy to maintain and aesthetically acceptable. The latest development in anodic materials is the use of carbon fibres (see photograph). Systems using data loggers and remote control are also on the increase. The use of solar cells, tapping into solar energy, with a battery as a buffer is increasingly widespread. At remote locations this can mean a considerable cost-saving because it removes the need to lay power cabling. These days CP is also being used on prestressed structures (bridges).
Recently, general understanding of the service life of CP has greatly increased. The latest development is numerical modelling of CP.