- Glass fiber reinforced concrete
Glass Fiber Reinforced Concrete (GFRC) is a type of
fiber reinforced concrete. Glass fiber concretes are mainly used in exterior building façade panels and as architectural precast concrete. This material is very good in making shapes on the front of any building and it is less dense than steel.
Glass fiber reinforced composite materials consist of high strength glass fiber embedded in a cementitious matrix. In this form, both fibers and matrix retain their physical and chemical identities, yet they produce 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.
The most common form in which fiber-reinforced composites are used in structural application is called a laminate. It is obtained by stacking a number of thin layers of fibers and matrix and consolidating them 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.
The potential for using a glass fiber reinforced concrete system was recognized by Russians in the 1940s. The early work on glass fiber reinforced concrete went through major modifications over the next few decades.
borosilicate glasscaused reduction in strength due to alkalireactivity with the cement paste. Alkali resistant glass fibers (AR glass) were then produced resulting in long term durability, but other strength loss trends were observed. Better durability result was observed when AR glass is used with a developed low alkaline cement.
The design of GFRC panels proceeds from a knowledge of its basic properties under tensile, compressive, bending and shear forces, coupled with estimates of behaviour 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 behaviour, 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. 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 the flanges 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 steel stud 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 all the sides of the steel frame are covered with two or several 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 pre-cast concrete, yet it is strong and durable and can easily be handled.
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