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Treatment of reinforcements with proper materials and agents one of the defensive layers against corrosion attacks in aggressive environments. There are many reinforcement treatment methods for instance anticorrosive treatment using acid or alkali agents and fusion bonded epoxy coating.
The basic principle of these treatment methods is to prevent the reaction between aggressive substance like chloride ions and steel reinforcement. hence, the time that needed for the reaching such harmful materials to steel bars are increase and consequently the durability of the structure is increased substantially.
The Anticorrosive treatment is applied after the rods are cut and bent to shape. The treatment is done in a covered area. The treated rods are stored above ground in a covered area on wooden / masonry supports. Average thickness of coating is 0.3 ± 0.1 mm. The procedure for anti-corrosive treatment of reinforcement is as follows:
- The reinforcement rods are immersed in de-rusting solution for about 15-30 minutes till rusts are removed and bright surface bars are achieved.
- De-rusting solution is prepared by mixing inhibitor-de-rusting solution plus hydrochloric acid plus water; a mix ratio of 5 liters inhibitor: 50-liter hydrochloric acid: 50 liters water can be used for the production of 100 liters of de-rusting solution can be considered.
- Then, remove the bars out of the solution, clean it with wet waste cloth.
- After that, immerse the bars in a solution which is produced by mixing alkaline powder with water; 1. Kg of powder shall be mixed with 400Liters of water. The bars should be left in this solution for 5 minutes then cleaned and removed.
- Phosphating Jelly is then immediately applied on the surface of the rods by means of a fiber brush. The jelly shall be allowed to react with the rod surface for 45-60 minutes and the jelly removed by means of rinsing in water or wet cloth.
- Corrosion inhibitor solution is then applied on the reinforcement surface by brushing/dipping.
- The corrosion inhibitor solution is mixed with ordinary portland cement in the ratio of 500 CC of inhibitor to 1 kg of OPC and a brushable slurry is prepared. This slurry is then be applied on the rod surface by brushing. All above steps should be applied in the same day and the steel allowed to air dry for 12 - 24 hours.
- Corrosion sealing solution is then be applied by brushing / dipping.
- Inhibitor is mixed with ordinary Portland cement in the ratio of 600 CC of inhibitor to 1 kg. of cement and a brushable slurry is prepared. This slurry is immediately applied on the reinforcement surface. The coating is then allowed to dry for 12 - 24 hours.
- Corrosion sealing solution is applied on the reinforcement surface. This coating is again repeated after 4 hours of air drying.
Fusion Bonded Epoxy Coating
This process shall be done as per IS: 13620. This process is carried out by the specialized agency in their Plant. The following procedure shall be considered when fusion bonded epoxy coating is used. More details regarding this treatment method can be found in IS: 13620.
- Clean the surface of steel bars with abrasive blast cleaning till near white surface is obtained. The surface profile shall be free from mill scale, rust and foreign matter when viewed under well-lit conditions.
- Apply coating to the cleaned surface as soon as possible. The maximum period between cleaning completion and start of applying coat is eight hours.
- The coating shall be applied as an electrostatically charged dry powder sprayed onto the grounded steel bar using an electrostatic spray gun.
- The powder may be applied to either a hot or cold bar.
- The coated bar shall be given a thermal treatment specified by the manufacturer of the epoxy resin that would provide a fully cured finish coating. Temperature shall be controlled to avoid blistering or other defects.
- 90 percent of all coating thickness measurements shall be 0.1 mm to O-3 mm after curing.
- The coating shall be visually inspected after curing for continuity of the coating and shall be free from holes, voids, contamination, cracks and damaged areas.
Commercially Available Corrosion Resistant Reinforcement
The reinforcement is purchased from well-known brand of corrosion resistant rods. The mechanical properties like tensile strength, elongation etc. should conform to the requirements of the corresponding class of bars, like Fe 415, Fe 500 etc. as per IS-1786.