Cathodic corrosion protection in reinforced concrete construction
Restoration principle K according to DAfStb Restoration Guideline
The principle of the cathodic corrosion protection (CCP) consists in the fact that as a result of a cathodic (negative) polarisation of the reinforcement which is forced by external current or contact with a less noble metal, existing potential differences on the reinforcement surface and thus the macrocell current driving the corrosion process are reduced (primary protective effect).
In addition to the primary protective effect, the so-called secondary protective effects result in an increase in pH value due to OH development on the reinforcement surface, which is now completely cathodic ("real alkalisation"). The chloride ion concentration on the steel surface is also reduced by ion migration to the anode in the applied electric field ("chloride removal").
The remaining corrosion rate is thus reduced to technically negligible or acceptable values without needing to remove the chloride-contaminated concrete. Only low strength or damaged areas (hollow layers, gravel nests, cracks, etc.) as well as areas with considerable cross-sectional losses of the reinforcement must be repaired locally in advance. Thus, the method is particularly suitable for buildings with a considerable chloride concentration down to great depths and for structural elements where, for static reasons, concrete cannot be removed or only with extensive stabilisation measures.
Tried and tested alternative to "classic" repairs
In 1985 a reinforced concrete structure was cathodically protected for the first time in Germany, so that now more than 30 years of practical experience in CCP are available. In addition to the repair guidelines of the German Committee for Reinforced Concrete, the procedure has been regulated since 2000 in EN 12696, which was converted into the international standard ISO 12696 in 2012.
In the case of large reinforced concrete structures, strip anodes or mesh anodes are usually used, which are applied to the prepared concrete surface and then embedded in a mortar specially tested for KKS and adapted to the structural concrete. In addition to the actual anode system, monitoring sensors are also installed, which enable constant maintenance and control of the success of the repair work. In this respect, ISO 12696 defines protection criteria which can be used to demonstrate sufficient polarisation to restore or maintain sufficient corrosion protection conditions for the steel in the concrete.
The protective effect of the system is evaluated on the basis of regularly conducted performance assessments and the protective current is adjusted if necessary. The costs for the power consumption of the system can be estimated at about 20 - 40 W / 1000 m2 and are thus in a negligible order of magnitude.
Our qualified and experienced employees plan and accompany your CCP repair measures in all work phases. CCP-specific preliminary tests can be carried out by our own test personnel and test laboratory. Dipl.-Ing. Benjamin Faber is a certified specialist planner for cathodic corrosion protection and holder of the Grade 2 certificate according to DIN EN 15257 covering the A4 scope of application (reinforced concrete facilities).