FRP coating consists of two or more engineered composite materials; it is essentially a composite of fibers, which serve as the reinforcing agent, and a polymer resin known as the matrix or binder. The fibers can be either short or long, each imparting specific properties to the final coating. The most well-known fibers are glass, carbon, aramid, and basalt. FRP fibers have high fire resistance and are fireproof coatings. They also have excellent tensile strength and high elongation. Therefore, they are used in a wide range of applications, including construction, aerospace, automotive racing, marine, military, defense, and medical industries.
Resins can be composed of thermoset and thermoplastic polymer materials. Polyester, vinyl ester, and epoxy are thermoset materials that, once formed, cannot be altered and will not melt or dissolve under any conditions. Thermoplastic materials, which are heat-softenable, can be made from polymer bases such as polyethylene, polystyrene, or nylons. FRP coating is highly valued due to its excellent properties such as high mechanical strength, low weight, good dimensional stability, resistance to moisture and corrosive chemicals, thermal insulation, and the ability to form complex shapes.
Applications of FRP Coating
The orientation of the fibers, which can be 90 degrees, 0 degrees, random, or any other degree, affects the final properties. For example, when forming an FRP coating with randomly oriented fibers and polyester resin, it will have good formability.
FRP coatings are used in various applications such as:
- Tanks for corrosive materials
- Storage tanks for wastewater and industrial effluents
- Reinforcing buildings with FRP coatings composed of glass fibers, which have high chemical resistance, insulating properties, and high tensile strength
Given recent forecasts, the volume of FRP industry sales is expected to grow significantly in the coming years, highlighting the importance of innovation and advancement in FRP production methods. Therefore, to enhance quality and reduce costs, polymer science must be carefully considered. The presence of fibers reduces the cost of structures and coatings while providing unique properties to the polymer base, and their lightweight nature is particularly significant.
In the automotive industry, FRP coatings are used for car bodies. The fibers used in this application are carbon fibers. Although carbon fibers are more expensive than steel bodies, their unique properties, such as lightweight, make FRP coatings particularly attractive. Over time, the cost is lower because their lightweight reduces fuel consumption, cutting fuel costs and helping the environment. This foresight results in lower long-term costs.
Features of FRP
- High corrosion resistance
- Fast implementation time
- No need for special maintenance
- Easy to install and implement
- Very lightweight
- Long-term economic efficiency
- Flexible
- Long useful life
- Environmentally friendly
- High elastic modulus
The disadvantages of FRP should also be considered alongside its positive features, and necessary research should be conducted to improve them. Issues such as reduced ductility compared to steel, due to the lack of a yield point before failure, should be addressed.
Types of FRP
FRP can be classified based on several factors, including the type of resin, the type of fiber, or the type of product and final application.
Product-based Classification:
- FRP Composite Rods: These rods replace steel rebar in construction, are lightweight, and have excellent strength, eliminating destructive issues in concrete structures such as carbonation and chlorination.
- FRP Composite Grids: This product is used to reinforce concrete by intersecting FRP rods in multiple directions.
- FRP Cables: Used in corrosive environments where high resistance and flexibility are needed, such as marine environments.
- FRP Composite Sheets: These sheets, with thicknesses in millimeters, have high strength and are resistant to corrosive materials, making them ideal for marine structures.
- FRP Structural Profiles: Produced in the form of angles and channels, these profiles replace heavy steel.
Fiber-based and Arrangement-based Classification
Glass Fibers
Also known as fiberglass, they have low density, low cost, resistance to moisture and oxidation, and are impermeable to water, making them suitable for water tank coatings. They soften and melt at around 850°C and have excellent resistance. These fibers are isotropic, maintaining properties across the transverse direction, and are the most commonly used fibers in FRP coatings, with several types including:
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- E-glass (Electrical glass fibers)
- A-glass
- S-glass (Structural glass fibers)
- R-glass
- D-glass
- C-glass (Chemical glass fibers)
- E-CR-glass
R-glass is more durable and expensive compared to other glass fibers.
Carbon Fibers
Known for low density, high tensile strength, high chemical resistance, minimal thermal expansion, and high stiffness, carbon fibers are more expensive than glass fibers. They can remain stable up to 2000°C if protected from oxidation above 1000°C. Carbon fiber coatings are used for applications requiring shear and bending resistance. They are much stiffer than glass fibers, but glass fibers have higher resistance.
Aramid Fibers
Lighter than carbon and glass fibers, with high chemical resistance, thermal stability, and flame resistance. However, they are sensitive to ultraviolet light and are carcinogenic, requiring careful handling.
Basalt Fibers
With a melting point between 1500 to 1700°C, these fibers are used in defensive and military coatings. Producing these fibers is cheaper than glass and carbon fibers due to lower energy consumption. Basalt fibers are less corrosive than glass fibers.
Resin-based Classification
Common resins used in FRP coatings, mainly in storage tanks, include polyester, vinyl ester, and epoxy. Polyester has low corrosion resistance, while vinyl ester has high corrosion resistance. Epoxy resin has high corrosion and temperature resistance, and the choice of resin or FRP composite base depends on the application environment.
Price of FRP Coating
FRP coatings are generally cheaper than traditional steel structures. They are highly resistant to corrosion, resulting in a long useful life and minimal maintenance costs, making the total cost much lower than traditional coatings. However, the price of FRP coatings is influenced by various factors due to the multiple components involved, such as fibers and polymer resin. The diversity in resin and fiber usage leads to different price estimates. Overall, the cost of FRP coatings is relatively lower compared to other coatings due to several features:
- Lightweight nature of FRP coatings reduces transportation and fuel costs, with a weight reduction of 25 to 70% compared to steel structures.
- The thin layer thickness occupies less space and is easy to install, resulting in lower final costs.
- Reinforcement with FRP coatings does not require much time, reducing execution costs.
- Lower fuel consumption during transportation of FRP coatings or use in vehicle bodies reduces fuel consumption, resulting in less CO2 emissions and lower environmental costs.
- The project location and execution space affect the price of FRP coatings.
Factors Affecting Price
The fibers can be bidirectional or unidirectional, affecting the final properties and the final price due to differences in the manufacturing process. Comparing the prices of FRP coatings based on the fibers used:
- Carbon fibers are more expensive than other fibers such as glass, basalt, and aramid due to their military applications and stability at high temperatures, making them valuable for defense industries. Although they are more expensive, using them in FRP coatings is recommended.
- Glass fibers come in various types, with E-glass being the cheapest and R-glass being the most expensive.
- Basalt fibers, with lower energy consumption and no need for additives, are cheaper than carbon and glass fibers, though their price varies depending on raw materials and manufacturing processes.
- Aramid or Kevlar fibers are also used in FRP coatings, but glass fibers remain cheaper.
- Epoxy resin, with its desirable properties such as high corrosion and temperature resistance, is more important than other resins, although it has a higher final cost.
- The volume, application thickness, and fiber percentage in each FRP coating also affect the final price, with increased volume and thickness requiring more materials, resulting in higher costs.
