Corrosion of steel reinforcements is one of the most significant challenges faced in the construction industry, particularly in aggressive environments such as coastal areas, industrial zones, and regions with high chloride or sulfate content. To combat this issue, proper treatment of reinforcements with specialized materials and agents serves as a critical defensive layer against corrosion attacks. By delaying the interaction between harmful substances like chloride ions and steel reinforcement, these treatments significantly enhance the durability and lifespan of structures. Two widely adopted methods for corrosion protection include anti-corrosive treatments using chemical agents and fusion-bonded epoxy coating.
Basic Principle of Reinforcement Treatment
The fundamental goal of reinforcement treatment is to prevent direct contact between aggressive substances, such as chloride ions, and the steel bars embedded within concrete. By creating a protective barrier around the reinforcement, these treatments increase the time required for corrosive agents to penetrate and reach the steel. This delay not only slows down the onset of corrosion but also substantially improves the structural integrity and service life of the building or infrastructure.
Anti-Corrosive Treatment
Anti-corrosive treatments are cost-effective and widely used in construction projects to protect steel reinforcement from rust and degradation. The process involves a series of chemical treatments that create a durable protective layer on the surface of the steel bars.
A. General Process
- The treatment is applied after the reinforcement rods are cut and bent into shape.
- All steps are carried out in a covered area to ensure proper environmental control.
- The treated rods are stored above ground on wooden or masonry supports to avoid moisture exposure.
- The average thickness of the final coating ranges between 0.2 mm and 0.4 mm (0.3 ± 0.1 mm).
B. Step-by-Step Procedure
- De-rusting:
- The steel bars are immersed in a de-rusting solution for 15–30 minutes until all rust is removed, leaving behind a bright, clean surface.
- The de-rusting solution is prepared by mixing an inhibitor-de-rusting solution, hydrochloric acid, and water in a ratio of 5 liters:50 liters:50 liters to produce 100 liters of solution.
- Cleaning:
- After de-rusting, the bars are removed from the solution and wiped clean using a wet cloth.
- Alkaline Treatment:
- The bars are then immersed in an alkaline powder solution (1 kg powder per 400 liters of water) for 5 minutes to neutralize any residual acids.
- The bars are cleaned again before proceeding to the next step.
- Phosphating Jelly Application:
- Phosphating jelly is applied immediately to the surface of the rods using a fiber brush.
- The jelly reacts with the rod surface for 45–60 minutes, after which it is rinsed off with water or a wet cloth.
- Corrosion Inhibitor Solution:
- A corrosion inhibitor solution is applied to the reinforcement surface via brushing or dipping.
- The inhibitor is mixed with ordinary Portland cement (OPC) in a ratio of 500 CC of inhibitor per 1 kg of cement to create a brushable slurry, which is then applied to the rods.
- Drying:
- The coated rods are left to air dry for 12–24 hours.
- Corrosion Sealing Solution:
- A second layer of corrosion sealing solution is applied using the same method. This solution is mixed with OPC in a ratio of 600 CC of inhibitor per 1 kg of cement.
- After drying for 12–24 hours, the coating is repeated after an additional 4 hours of air drying.
Fusion Bonded Epoxy Coating
Fusion-bonded epoxy (FBE) coating is a highly effective method for protecting steel reinforcements against corrosion. This process is typically carried out in specialized plants under controlled conditions and adheres to standards such as IS: 13620.
A. Standards and Guidelines
The entire process must comply with IS: 13620, ensuring consistency and quality in the application of the epoxy coating.
B. Procedure
- Surface Preparation:
- The steel bars are cleaned using abrasive blast cleaning to achieve a near-white surface.
- The cleaned surface must be free from mill scale, rust, and foreign matter when inspected under well-lit conditions.
- Coating Application:
- The epoxy coating is applied within 8 hours of completing the cleaning process.
- The coating is applied as an electrostatically charged dry powder sprayed onto the grounded steel bar using an electrostatic spray gun.
- The powder can be applied to either hot or cold bars, depending on the manufacturer’s specifications.
- Thermal Treatment:
- The coated bars undergo thermal curing at temperatures specified by the epoxy resin manufacturer.
- Proper temperature control is essential to avoid defects such as blistering or cracking.
- Quality Control:
- After curing, 90% of the coating thickness measurements should fall within the range of 0.1 mm to 0.3 mm.
- Visual inspection ensures the coating is continuous and free from holes, voids, contamination, cracks, or damaged areas.
Commercially Available Corrosion-Resistant Reinforcement
In addition to on-site treatments, contractors can opt for commercially available corrosion-resistant reinforcement. These products are manufactured by reputable brands and are designed to meet specific mechanical property requirements, such as tensile strength and elongation, as outlined in IS-1786. Common grades include Fe 415 and Fe 500, making them suitable for a wide range of construction applications. Purchasing pre-treated reinforcements eliminates the need for on-site treatment, saving time and ensuring consistent quality.
Conclusion
The treatment of reinforcements is a crucial step in ensuring the longevity and durability of structures exposed to aggressive environments. Anti-corrosive treatments using chemical agents and fusion-bonded epoxy coatings are two of the most effective methods for protecting steel reinforcements against corrosion. Both methods provide a robust barrier that delays the penetration of harmful substances, thereby extending the service life of the structure. Adherence to established standards, such as IS: 13620, and rigorous quality control measures are essential to achieving optimal results. By investing in proper reinforcement treatment, builders can significantly reduce maintenance costs and enhance the safety and reliability of their projects.