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Using FRP in Architecture

FRP: Fiberglass Reinforced Plastic

GFRP: Glassfiber Reinforced Plastic


Introduction:


FRP (or GFRP) is a generic term for the composite of a polymer matrix reinforced with fibers. The fibers impart strength and stiffness to the composite and also act as crack stoppers. The matrix binds the fibers together, transferring loads from fiber to fiber. The matrix also protects the fibers from mechanical abrasion and chemical reactions with the environment. In principle, FRP material can be formed into any shape – it has no inherent form. In architectural applications of FRP the choice of manufacturing process is influenced by many factors including:

  • Geometry

  • Engineering requirements

  • Shape repetition

  • Shipping/transportation capabilities

  • Installation equipment and capabilities

  • Maximum unit size

  • Surface finish

The most commonly used composition of fiber and matrix is glass fiber and polyester resin. These materials offer a good combination of strength, stiffness and economy. Carbon fiber with epoxy resin, can provide very high strength to weight but because of its cost is generally only used in very high performance applications. Vinyl ester resin can provide superior corrosion resistance, but usually far in excess of what is required for building cladding.


Mechanical Properties:


Actual properties of a composite vary with the types of reinforcements, matrices, cores, fillers, and so on. Some general guidelines assuming glass fiber and polyester resin are as follows:

  • Density: 90 pcf

  • Water Absorption: <0.1%

  • Compressive strength: 23,000 to 29,000 psi

  • Flexural strength (ultimate): 30,000 to 35,000 psi

  • Modulus of elasticity: 2.4 x 106 psi

  • Tensile strength (ultimate): 25,000 to 39,000 psi

  • Coefficient of thermal expansion: 11 x 10-6 in./in./deg F


Advantages/Disadvantages:


Advantages of FRP include:

  • Lightweight – FRP is extremely light weight and can achieve similar structural performance to GFRC with less thickness.

  • Flexibility – FRP is more resilient than GFRC and does not present the same brittleness and cracking issues.

  • Customizable properties – Panel thickness, orientation of reinforcement, integral stiffeners, core material and thickness, etc is routinely engineered and customize to efficiently meet performance criteria.

  • Durability and corrosion resistance – properly fabricated FRP does not rot like wood or rust like steel and has very good resistance to chemical corrosion.

Disadvantages of FRP include:

  • Experience – Less experience with FRP as a façade material in the construction industry.

  • Combustibility – FRP is less resistant to fire than, say, cement-based or metal alternatives, however recent technological advancements have overcome this as a barrier to its use as building cladding.

  • Complexity – Properly choosing from among the thousands of combinations of fibers, matrices, additives, cores, etc, requires specialized fabrication and engineering knowledge.

Form and Finish:


The surface texture of a molded product is a direct reflection of the surface of the mold used to produce it. Further hand finishing can be done after molding. A surface coating can be incorporated in the molding processing using resin compatible with the matrix resin (this is termed a gel-coat). Polyester gel-coats are chosen for external exposure. They have good color fastness. Alternatively, an item can be painted post mold. Paints are typically polyurethane. It is possible to manufacture translucent FRP by using glass fiber reinforcement and an appropriate clear matrix polymer. Final finish surfaces can range widely from smooth and glossy to cratered and rock-like.

Some possible FRP finishes: polymer concrete, glossy, and translucent