BBV Systems

Cathodic Protection

Cathodic corrosion protection of steel in concrete structures

The cathodic corrosion protection (CP) by protection current is a modern, gentle and intelligent way of treating concrete structures with corrosion problems.

CP has proven to be an effective method in many countries to prevent or prevent the loss of concrete reinforcement due to corrosion. Several million m² of cathodically protected concrete surface worldwide prove the success of this process. Protective current CP has evolved and improved over the years, both in terms of materials and systems available, and in terms of system design, operation and monitoring. The standard for the application of cathodic corrosion protection to reinforced concrete structures is DIN ISO EN 12696: 2012.  

The conventional way of repairing concrete structures with reinforcement corrosion is the removal of cracked or chipped concrete areas and the replacement of the rusted reinforcement. In cases where the damage is limited and thus the problem of a local nature, such an approach may be sufficient. However, this procedure often requires the removal of large parts of otherwise healthy concrete. Another problem is the durability of such repairs.

In a CP application, the extent of concrete removal is significantly lower and the quality / resp. the effect can be permanently detected and quantified by built-in sensors. For the duration of the CP operation, the current state of the building is virtually frozen. The remaining life of the structure is thus extended as long as the protection current is maintained.


Corrosion

First signs of corrosion at the reinforcement in concrete structures are usually slight cracks in the concrete cover and / or partial signs of rust color.

This is followed by more pronounced cracks and possibly spalling, as the corrosion products have a 5-7 times larger volume than steel.

The more the concrete is weakened and the cracks also make it more open, the more the penetration of pollutants is promoted. In extreme cases, the loss in the steel cross-section leads to a reduction in the tensile strength of the reinforcement and ultimately to a disruption of the system.

Steel in normal concrete, without pollutants will not corrode due to its passivity. An atomic thin iron oxide layer on the steel surface, which is kept stable by the pH of the concrete (about 13), causes the steel to be in a state of negligible corrosion.

The passivation can be broken by two mechanisms (promoted by sufficient moisture and available oxygen):

• Carbon dioxide action, which reduces the pH and causes a uniform, areal loss of passivation (= corrosion induced by carbonation)

• presence of chloride ions, which locally break through the passive film and cause pitting corrosion (= chloride-induced corrosion by, for example, salt salts, accelerators, etc.)


 

Cathodic corrosion protection

Cathodic protection is an electrochemical protection process in which an electrical direct current flows through the electrolyte (pore water solution in the concrete) onto the reinforcement to be protected. Through this protection current, the main effect is cathodic polarization at the surface of the reinforcement, i. there is a shift of the electrochemical potential "E" of the steel towards more negative values. This prevents metal ions from being released from the metal surface (see Corrosion). The anodic partial process (iron dissolution) of the corrosion is suppressed or prevented (metal removal rate <0.01 mm / A). The result is a change in the potential to values ​​at which the entire steel becomes cathodic compared to the anode, hence the term "cathodic protection".

The operation of a PPS system creates an electric field between the reinforcement and the anode, which in addition to the change in potential results in two more positive side effects in the vicinity of the steel. Under the influence of the field, all negatively charged ions (OH, CL, SO42) migrate away from the reinforcement towards the anode. Although this electromigration is limited under normal CP operation, there is some distance between the chloride ions and the steel surface, which significantly reduces the risk of further corrosion. As a second side effect it turned out that at the current densities commonly used for PPS, a thin layer of (carbonated) concrete around the steel is reallocated (pH increase). The steel is brought into a more passive state, whereby the corrosion can no longer be triggered or continue to progress. This effect was observed even at low chloride concentrations.

In the CP-C, an anode is placed on / in the concrete (s), either drilled, slotted or mounted on the surface. It is connected to the positive pole and the reinforcement to the negative pole of a voltage source. Before attaching the anode, various controls must be performed, such as measuring the continuity of the reinforcement.

To assess the quality of protection provided by the applied current, sensors are installed near the steel. There are different types of sensors. The most common are reference electrodes (RE). These electrodes measure the electrochemical potential in relation to a known potential. The most widely used and accepted criterion for demonstrating the effectiveness of PPS is the 100 mV depolarization (turn-off) criterion. It indicates that the steel is sufficiently protected when a potential drop of min. 100 mV is recorded over a period of 24 hours after the power has been switched off. It should be noted that each reading reflects only the location where the reference electrode is placed. It is important that the REs are placed in representative places and in sufficient numbers (> 1 RE per 100 m2).


Anode systems

Depending on the location and the associated situation of the reinforcement to be protected, the following anode types / systems can be used:

  • Titanium mesh anodes
  • Titanium bracelet anodes
  • Titanium discrete anodes
  • Conductive coating system

Advantages

High efficiency da / due

  • no removal of chloride contaminated concrete necessary
  • low energy expenditure
  • less noise pollution
  • less vibrations
  • little interference with the structure and environment
  • Repair possible during ongoing operation
  • little disturbance of the environment / environment
  • shorter construction time

Especially for parking garages / underground garages:

  • Low rental loss
  • No full locking of a parking level

High sustainability / traceability by

  • continuous operation
  • continuous monitoring through built-in sensors
  • regular maintenance

Our range of services

  • Advice during the planning of a repair
  • Preliminary investigations
  • System design and detailed planning of a CP plant
  • Execution CP-C
  • Operation
  • Maintenance (cost-effective with the help of remote data transmission)

 

Corrosion with rusted away distribution rebars

Corrosion mechanism

100 MV Depolarisation criteria

 

Reference-electrode