COATING & CATHODIC PROTECTION
Cathodic protection and corrosion inhibitors will be considered to mitigate the corrosion of reinforced steel. Cathodic protection (CP) is a method wherein a sufficient amount of electric direct current (DC) is continuously supplied to a submerged or buried metallic structure to mitigate, slow down or temporarily stop the natural corrosion processes from occurring.
Engineering Solution: Coatings and Cathodic Protection
Cathodic Protection
Cathodic protection is a method wherein a sufficient amount of electric DC current is continuously supplied to a submerged or buried metallic structure to mitigate, slow down or temporarily stop the natural corrosion processes from occurring. The DC current corrodes a sacrificial anode when it is connected to a structure to be protected.
Coatings Application
Consideration should be given to coatings for repair prior to replacement of the components of the reinforced concrete structure. This will include alternative materials to non-concrete materials and maintenance coatings.
Early detection & Mitigation
If accelerated corrosion is captured early on coating application and cathodic protection can mitigate the accelerated corrosion with low costs
Thermal Spray Coating Application
Consideration should be given to application of thermal spray zinc or thermal spray aluminum-zinc coatings to mitigate the corrosion of steel reinforcement that exhibit accelerated corrosion. Zinc thermal spraying is a process in which zinc or zinc alloys are melted and sprayed onto a prepared concrete substrate – offers a highly effective, long lasting means of corrosion protection in a variety of applications and environments including C4 and C5 (aggressive industrial marine environment).
Team Matergenics can apply these types of coating and monitor the corrosion prior and after application of the thermal spray by wireless corrosion sensors. Our Thermal Spray Specialist has over thirty years experience in important this important field for corrosion mitigation of aging concrete infrastructures
Coating to Mitigate Corrosion
highly effective, long lasting means of corrosion protection in a variety of applications and environments
SCIENCE BEHIND CATHODIC PROTECTION
There are two methods for supplying DC to cathodically protect a structure. They are the following:
- Galvanic or sacrificial anode cathodic protection system (SACP).
- Impressed current cathodic protection system (ICCP).
The galvanic anode cathodic protection system generates DC as a result of the natural electrical potential difference (electrochemical reaction) between the metal to be protected (cathode) and another metal to be sacrificed (anode). The sacrificing metals such as magnesium (Mg), zinc (Zn) or aluminum (Al) all have a lower more negative electrical potential with respect to carbon steel reinforcement. The current output of this system is affected by factors such as:
- Driving voltage difference between the anode and the
- Resistivity of the electrolyte (environment).
- pH
- Natural or man-made environmental chemistry and/or
The impressed current cathodic protection system comprises four main components which together constitute an electrical circuit. They are as follows:
- A controllable DC power source – usually a transformer
- An applied anode – a material placed onto or into the concrete or surrounding electrolyte to enable current
- An electrolyte – normally the pore water present within the concrete, or in the case of remote anodes, also the water, soil or mud in which the anodes are
- A return electrical path – normally the electrically continuous reinforcement steel to be
Please review case histories for corrosion risk assessment of aging buildings and corrosion mitigation in the following reference published by Dr, Zee, our expert in condition assessment.
Design of Suitable Corrosion Protection Measures to Mitigate Corrosion of steel Reinforcement
There are two methods for supplying DC to cathodically protect a structure. They are the following:
- Galvanic anode cathodic protection system.
- Impressed current cathodic protection system.
GALVANIC ANODE CP SYSTEM
Generates DC as a result of the natural electrical potential difference (electrochemical reaction) between the metal to be protected (cathode) and another metal to be sacrificed (anode). The current output of this system is affected by factors such as:
- Driving voltage difference between the anode and the cathode.
- Resistivity of the electrolyte (environment).
- pH factor.
- Natural or man made environmental chemistry and/or contaminates.
IMPRESSED CURRENT CP SYSTEM
Four main components:
- A controllable DC power source – usually a transformer rectifier.
- An applied anode – a material placed onto or into the concrete or surrounding electrolyte to enable current flow.
- An electrolyte – normally the pore water present within the concrete, or in the case of remote anodes, also the water, soil or mud in which the anodes are placed.
- A return electrical path – normally the electrically continuous reinforcement steel to be protected.
The CP transformer rectifier can be powered by external power sources, such as alternating current (AC). The CP rectifier converts the input power source into DC. DC is discharged from impressed current anodes. The current output of an impressed current cathodic protection system is far greater than the current output of a galvanic anode cathodic protection system. However, higher maintenance during service is required.
