Well, the last blog was all about the prevention of corrosion on reinforcement steel bars and two methods used for the prevention were described, but only one method was fully detailed. The other method is detailed right here. Let’s buckle up.
Fusion Bonded Epoxy Coating
Fusion Bonded Epoxy (FPE) coating is a process where the epoxy powder is applied by electrostatic spray on hot steel at pre-set temperature level. It is also called powder coating. Normally this method should conform to IS:13620 standards. The name Fusion Bond Epoxy is termed due to the cross-linking property of resin and it’s application method, which is different from conventional paints. This procedure is an irreversible process and provides the protection to reinforced steel bar against corrosion. It prevents the attack of chloride ion on the metallic surface and occurrence of electrochemical reaction initiating the corrosion of steel.
Fusion-based epoxy coating was started in the 1960s and has undergone several changes to meet different types of requirement. The main components of FBE are:
- Hardener or curing agent
- Fillers and extenders
- Colour pigments
The resin and hardener combined together are called the binder. The resin part is called epoxy. Both the resin and hardener components in the dry powder FBE stock remain unreacted at normal storage conditions.
So, how does the dry powder content assumes the liquid form and why is this whole process irreversible? Well, it’s simple, heating.
The typical coating application temperatures are usually in the range of 180 °C to 250 °C. During this temperature, the contents of the powder melt and transform into liquid form. The liquid substance wets and flows onto the steel surface on which it is applied, and soon becomes a solid coating by a chemical cross-linking process, which is further assisted by heat. This process is known as Fusion Bonding. Once this process takes place, the coating cannot be returned to its original form by any means.
Fusion bonded epoxy coating application generally has three essential stages:
- Cleaning of the steel surface
- Heating the steel according to the recommended FBE temperature
- Application and the curing stage
For the preparation of the steel bar, Blast cleaning is the commonly used technique. This method effectively removes rust, scale etc., from the surface and produces an industrial grade cleaning and a rough surface finish. In the next stage, the steel is heated to the required FBE coating application temperature.
The temperatures are usually in the range from 225 °C to 245 °C. During this process, the FBE powder is sprayed onto the reinforced bar using an electrostatic spray gun. The FBE powder undergoes melting onto the pipe surface and dries quickly in controlled and uniformed thickness.
Corrosion, although it is a slow process, is often called cancer in concrete because of the extensive damages caused on the inside the reinforcement bars rather than on the outside. By following these mentioned measures, corrosion can be prevented to an extent.