What are Corrosion inhibitors?
Corrosion inhibitors for concrete are specialized chemicals designed to decrease the rate of corrosion of steel reinforcement within concrete structures. Various types of corrosion inhibitors, such as calcium nitrite, amino alcohols, and sodium mono-fluorophosphates, have been developed to address different corrosion mechanisms, including those triggered by concrete chloride contamination and carbonation.
They are typically classified into anodic, cathodic, and mixed types based on their mechanism of action. Selection depends on the specific conditions and requirements of the concrete structure in question.
What are Corrosion inhibitors used for?
How do Corrosion inhibitors work?
Corrosion inhibitors for concrete function by either physically or chemically interacting with the steel reinforcement surface to prevent or mitigate the corrosion process.
Anodic inhibitors create a passive layer on the steel surface. Cathodic inhibitors selectively precipitate on cathodic regions to interrupt electron flow from anode to cathode and reduce the corrosion potential. Mixed inhibitors affect both cathodic and anodic reactions by adsorbing on the steel surface, forming a protective layer and reducing the corrosion rate without significantly changing the corrosion potential.
These inhibitors can be mixed directly into the repair concrete, applied directly to the exposed reinforcement steel or applied to the surface of existing structures. When mixed into the concrete, they interact chemically or electrochemically with the steel surface. When applied to the concrete surface, they migrate through the concrete to reach the metal reinforcement, forming an adsorbed film that prevents corrosive agents from directly contacting the steel surface.
Certain inhibitors work by absorbing oxygen, reducing its availability for the corrosion reaction or by altering the pH of the environment to make the conditions less favourable for corrosion. Organic compounds such as amines and alkanolamines have been found effective in both preventing and mitigating corrosion in medium and low concentrations of chloride ions.
The effectiveness of a corrosion inhibitor depends on the specific environment, the material being protected, and the type of inhibitor used.
How do I repair concrete structures using corrosion inhibitors?
A simple step by step guide to repair concrete structures using corrosion inhibitors to BS EN 1504 is provided below:
Conduct a thorough assessment of the concrete structure to identify the extent and type of damage and the repairs needed including the determination of chloride ion penetration or carbonation depth, if applicable.
Clean the affected areas and remove any deteriorated concrete.
Select either surface applied corrosion inhibitors that penetrate the concrete to reach the reinforcement steel or those which require removal of cover concrete.
For surface-applied corrosion inhibitors apply via spraying, rolling, or brushing, ensuring even coverage on clean and, if necessary, pre-wetted concrete surfaces. Spraying is preferred for large areas due to its efficiency, while rolling and brushing are suitable for smaller or detailed areas. Post-application, the inhibitor should dry as per the manufacturer’s guidelines, which may vary with environmental conditions. Some inhibitors may also require specific curing conditions to activate effectively.
For internally applied corrosion inhibitors, remove the cover concrete to expose and clean the reinforcement steel and either directly apply corrosion inhibitors to surface or mix them into the repair concrete. If necessary, apply a bonding primer to the prepared substrate to ensure adhesion between the old concrete and the new repair material. Mix and apply the repair mortar or concrete according to the manufacturer's instructions, ensuring full encapsulation of the reinforcement and complete filling of the repair area. Finish the surface of the applied repair material to match the surrounding concrete in texture and colour, and cure properly to ensure optimal strength development and durability.
Conduct quality control checks during and after the repair process to evaluate the effectiveness of the corrosion protection provided.
Document all materials used, application methods, and quality control measures taken during the repair process.
What equipment and expertise are required for repairing concrete structures using corrosion inhibitors?
For surface applied corrosion inhibitors, all that is required is the corrosion inhibitor solution, a low-pressure sprayer or paint rollers/ brushes to apply it to the concrete surface, and PPE such as gloves, safety glasses, and respirators to ensure the work can be done safely and protect workers from chemical exposure.
Internally applied corrosion inhibitors require tools such as hydraulic breakers, jackhammers, chipping hammers, concrete saws and angle grinders to remove the cover concrete and scarifiers or needle scalers to prepare the surface for high strength bonding with the repair materials.
For inhibitors applied directly to the exposed steel wire brushes or sandblasting rigs are required to clean and prepare the steel surface before brushes or sprayers are used to apply the compound.
A concrete mixer will be required to prepare the repair concrete and accurate weigh scales to ensure the correct composition including any corrosion inhibiting admixtures.
Applying surface-applied corrosion inhibitors generally requires the least expertise and equipment, involving straightforward techniques like spraying, rolling, or brushing, along with basic surface preparation knowledge.
Conversely, applying inhibitors directly to exposed steel or mixing them into repair concrete demands more specialized skills, such as understanding detailed mixing ratios, thorough steel surface preparation, and precise application methods to ensure effectiveness. These methods necessitate a deeper knowledge of concrete repair and corrosion protection principles, as well as familiarity with the specific properties and requirements of the chosen corrosion inhibitors, to successfully extend the lifespan of concrete structures.
What are the advantages of repairing concrete structures using corrosion inhibitors?
Corrosion inhibitors delay the onset of steel corrosion within concrete structures exposed to environmental aggressors like chlorides and carbon dioxide, thereby extending the preventative phase before maintenance becomes critical.
The application of corrosion inhibitors contributes to a noticeable extension of the structure's lifecycle, offering economic benefits by deferring the substantial costs associated with extensive repairs or total replacement.
This is a simple, easy repair method to carry out especially when using surface applied inhibitors which can simply be painted on.
What are the disadvantages of repairing concrete structures using corrosion inhibitors?
Environmental exposure may lead to the leaching of inhibitors from the concrete matrix, gradually diminishing their protective capabilities and necessitating reapplication or alternative protection strategies.
Achieving the optimal balance in inhibitor concentration is pivotal; deviations can lead to suboptimal protection or, conversely, adverse reactions within the concrete matrix, emphasizing the need for precise formulation and application according to manufacturers' guidelines.
When steel reinforcement is exposed, contamination can find its way deep within the concrete and even under the applied inhibitor reducing its effectiveness or possibly allowing the development of new types of deterioration.
What are the limitations of repairing concrete structures using corrosion inhibitors?
Once corrosion has initiated, the effectiveness of corrosion inhibitors may diminish, presenting challenges in halting or reversing existing damage.
The application of some traditional inhibitors, especially those containing nitrites, must be critically assessed for environmental compatibility and potential health risks, advocating for a careful selection of green, sustainable alternatives where possible.
The protective efficacy of corrosion inhibitors is highly contingent upon accurate application techniques and adherence to specified dosages.
Guaranteeing the prolonged effectiveness of corrosion inhibitors within dynamically changing environmental conditions and evolving structural stresses demands a comprehensive understanding of the interaction between the concrete microenvironment and inhibitor chemistry.
Ancillary information
Service disruption: Yes
Preliminary works: Yes
Posterior works: Yes
Time consumption: Medium
Cost: Medium
References and further information