What is GRC: Glass Fiber Reinforced Concrete ?
Glass Fiber Reinforced Concrete (GFRC), also known as GRC, is a type of fiber reinforced concrete. Glass fiber concretes are mainly used in exterior building façade panels and as architectural precast concrete.
It is one of the most versatile building materials available to architects & Engineers. It consists of fine aggregates, cement, water, chemical admixtures and special alkali resistant glass fibres. It is used to manufacture high strength, thin sectioned, prefabricated products
Glass fiber reinforced concrete (GFRC) consists of high strength glass fiber embedded in a cementitious matrix. In this form, both fibers and matrix retain their physical and chemical identities, while offering a synergism: a combination of properties that can not be achieved with either of the components acting alone. In general, fibers are the principal load-carrying members, while the surrounding matrix keeps them in the desired locations and orientation, acting as a load transfer medium between them, and protects them from environmental damage. In fact, the fibers provide reinforcement for the matrix and other useful functions in fiber-reinforced composite materials. Glass fibers can be incorporated into a matrix either in continuous lengths or in discontinuous (chopped) lengths.
A widely used application for fiber-reinforced concrete is structural laminate, obtained by adhering and consolidating thin layers of fibers and matrix into the desired thickness. The fiber orientation in each layer as well as the stacking sequence of various layers can be controlled to generate a wide range of physical and mechanical properties for the composite laminate. However, GFRC cast without steel framing is commonly used for purely decorative applications such as window trims, decorative columns, exterior friezes, or limestone like wall panels.
The potential for using a glass fiber reinforced concrete system was recognized by the Soviets in the 1940s. The early work on glass fiber reinforced concrete went through major
The design of GFRC panels proceeds from a knowledge of its basic properties under tensile, compressive, bending and shear forces, coupled with estimates of behavior under secondary loading effects such as creep, thermal and moisture movement.
There are a number differences between structural metal and fiber-reinforced composites. For example, metals in general exhibit yielding and plastic deformation whereas most fiber-reinforced composites are elastic in their tensile stress-strain characteristics. However, the dissimilar nature of these materials provides mechanisms for high-energy absorption on a microscopic scale comparable to the yielding process. Depending on the type and severity of external loads, a composite laminate may exhibit gradual deterioration in properties but usually would not fail in catastrophic manner. Mechanisms of damage development and growth in metal and composite structure are also quite different. Other important characteristics of many fiber-reinforced composites are their non-corroding behavior, high damping capacity and low coefficients of thermal expansion.
Glass fiber reinforced concrete architectural panels have general appearance of pre-cast concrete panels, but are different in several significant ways. For example, GFRC panels will, on the average, weigh substantially less than pre-cast concrete panels due to their reduced thickness. The low weight of GFRC panels decrease superimposed loads on the building’s structural components. The building frame becomes more economical.
A sandwich panel is a composite of three or more materials bonded together to form a structural panel. It takes advantage of the shear strength of a low density core material and the high compressive and tensile strengths of the GFRC facing to obtain high strength to weight ratios
The theory of sandwich panels and functions of the individual components may be described by making an analogy to an I-beam. Core in a sandwich panel is comparable to the web of an I-beam, which supports theflanges and allows them to act as a unit. The web of the I-beam and the core of the sandwich panels carry the beam shear stresses. The core in a sandwich panel differs from the web of an I-beam in that it maintains a continuous support for the facings, allowing the facings to be worked up to or above their yield strength without crimping or buckling. Obviously, the bonds between the core and facings must be capable of transmitting shear loads between these two components thus making the entire structure an integral unit.
The load carrying capacity of a sandwich panel can be increased dramatically by introducing light steel framing. The light steel stud framing will be similar to conventional steel stud framing for walls, except, that the frame is encased in a concrete product. Here, sides of the steel frame are covered with two or more layers of GFRC, depending on the type and magnitude of external loads. The strong and rigid GFRC provides full lateral support on both sides of the studs, preventing studs from twisting and buckling laterally. The resulting panel is light weight in comparison with traditionally reinforced concrete, yet is strong and durable and can be easily handled
Light weight: Although GRC has a similar density to concrete the products made from it are many times lighter due to the thin 10-15mm skin thickness used. A cladding panel manufactured from 100mm thick precast concrete would weigh 240kgs per m2 compared to a similar GRC panel of 40-50kgs/m2.
In fact many GRC products can be lifted and carried by hand an important consideration with strict manual handling regulations now being introduced in many countries.
Appearance: GRC has a wide flexibility in design and manufacture, which enables it to reproduce most architectural styles and features. It can replicate virtually any surface detail and reproduce the appearance of materials such as stone, slate, terracotta and marble. Carved stonework involves specialised skills and is slow to produce making the end product expensive.
GRC can match stonework in appearance and as it can be produced in thin sections it is easier to handle and fix.
Cost effective: GRC Products have been shown to provide economic solutions to many applications.
Although the manufacturing costs may be higher than say concrete when the reduced handling, transport and fixing costs are considered there can be an overall saving.
Corrosion and rot proof: GRC products do not contain mild steel reinforcement and the problems associated with corrosion of reinforcement do not apply.
GRC is unaffected by external exposure and will not rot. It is completely unaffected by exposure to UV light.
Incombustible: Most GRC formulations comply with non-combustible criteria for UK and EU standards.
Polymer GRC is not classed as non-combustible but conforms to the requirements of Class O defined by the British Building Regulations.
Hand Spray is the most versatile and popular production technique and the one normally chosen by new start-ups. A special spray gun is used to simultaneously deposit chopped glass fibre and cementitious slurry onto a mould.
This is then compacted by hand using a spring roller. A second layer is then sprayed and again compacted. Using the spray technique allows high glass percentages to be used and this gives the highest mechanical properties. In turn this allows for reduced skin thickness and lighter products.
Auto Spray: The hand spray process can be automated or semi-automated. More common are semi-automatic processes where the spray gun is mounted on a reciprocating traverse with the moulds passing underneath on a conveyor.
Compaction can be by hand or via a dewatering system. These systems are ideal for the production of flat products and they can also be very versatile when used with folding moulds.
Cast Premix: As the name suggests the glass fibre is mixed into the cementitious slurry and the resulting material is poured or pumped into moulds and compacted using vibration or by using special additives in the mix.
The premix process can be easily automated and is often chosen for standard product manufacture. The moulds used are more complex than those for the spray process. The mechanical properties are lower but they are consistent allowing optimum design.
Sprayed premix: This is a combination method where the premixed material is sprayed onto the mould.
It combines the advantages of both methods and is becoming the method of choice for many small architectural items.
( Reference http://fibretech.org/, Wikkipedia )