The corrosion phenomena affecting reinforced concrete structures are well known to the experts in the field. The steel reinforcement inserted in the cementitious structures to improve the mechanical properties thereof normally works in a passivation regime induced by the concrete alkaline environment; however, after some time, the ion migration across the porous surface of the concrete induces a localised attack to the protective passivation film. Another form of concrete decay is represented by the phenomenon of carbonatation, i.e. the formation of calcium carbonate by reaction of the lime in the cementitious mixture with atmospheric carbon dioxide. The calcium carbonate lowers the alkali content of the cement (from pH 13.5 to pH 9) bringing iron to an unprotected status. The most common method to extend the lifetime of reinforced concrete structures exposed to atmospheric agents consists of the cathodic polarisation of the steel reinforcement. In this way, the latter becomes the site of a cathodic oxygen reduction, thereby suppressing the corrosion and dissolution anodic reactions. This system, known as cathodic protection of reinforced concrete, is carried out by coupling anodic structures of various kinds to the concrete, in whose respect the reinforcement to be protected acts as the cathodic counterelectrode. The electrical currents involved, supplied by an external rectifier, transit across the electrolyte consisting of the porous concrete partially soaked with salty solution. It is known that the cathodic protection of a reinforcement cage may be achieved by means of a distributed anode system, for instance consisting of an arrangement of mesh strip anodes, installed on the reinforcement cage and electrically insulated from the metal by means of spacers made of plastic or cementitious material. The anode system is embedded into the structure during the construction, at the time of casting the concrete. A weak direct current (typically 1 to 30 mA per m2 of reinforcement) applied to the anode and distributed across the whole structure imposes the cathodic potential required for the reinforcement protection.
The application of prefabricated insulating spacers of plastic or cementitious material to valve metal anodes in form of mesh strips has been disclosed in which the spacers are generally secured in a first step to the metal cage to be protected. The anode strips are subsequently secured to the spacers, for instance by insertion in appropriate slits provided in the spacers. Alternatively, the step of securing the anode strips to the spacers may be carried out by way of pins, bolts or clips, or by using adhesives. This operation is apparently lengthy and cumbersome, especially in those spots offering a less comfortable installation due to a difficult access or to an insufficient lighting. This operation also presents a certain risk of error, because an accidental mistake in the positioning or in the fixing step may cause the anode strip to be locally put in electrical contact with the metal reinforcement cage.
Another kind of discrete spacer for anode strips employed in the cathodic protection of reinforced concrete has been disclosed wherein parallelepipeds of cementitious material with embedded insulating fibres, obtained by moulding, are positioned on the structure to be protected before laying down the anodes. Also in this case, the overall operation appears laborious, scarcely practical in zones of difficult access and not exempt from risks of error. The cementitious spacer is stiff and has a predefined length, which limits its use to not-too-complex structures.