Glass Fibre Concrete: Investigation on Strength and Fire Resistant Properties

Abstract

Over the decades, there has been a significant increase in the use of fibres in concrete for improving its properties such as tensile strength and ductility. The fibre concrete is also used in retrofitting existing concrete structures. Among many different types of fibres available today, glass fibre is a recent introduction in the field of concrete technology. Glass fibre has the advantages of having higher tensile strength and fire resistant properties, thus reducing the loss of damage during fire accident of concrete structures. In this investigation glass fibres of 450 mm length are added to the concrete by volume fraction of up to 1% to determine its strength and fire resistant characteristics. Comparison of the strength and fire-resistance performance of conventional concrete and glass fibre concrete was made. The paper presents the details of the experimental investigations and the conclusions drawn there from. Generally, concrete is strong in compression and weak in tension. Concrete is brittle and will crack with the application of increasing tensile force. Once concrete cracks it can no longer carry tensile loads. In order to make concrete capable of carrying tension at strains greater than those at which cracking initiates, it is necessary to increase the tensile strength. To increase the tensile and flexural strength, fibres are added in concrete. The addition of fibres to concrete will result in a composite material that has properties different from those of un-reinforced concrete. The extent of this variation depends not only on the type of fibres, but also on the fibre dosage. The incorporation of fibres into a brittle concrete can have the effect of controlling the growth and propagation of micro cracks as the tensile strain in the concrete increases. Care is needed in using fibre as additive in concrete. The use of fibres in concrete has increased with the development of fast-track construction. In fact, nearly 65 per cent of the fibres produced worldwide is currently used in concrete. It offers increasing toughness and ductility, tighter crack control and improved load-carrying capacity. Different types of fibres are available in the market for reinforcing concrete and they are: steel, glass, acrylic, aramid, carbon, nylon, polyester, polyethylene, polypropylene, etc. Besides, natural fibres like sisal, wood cellulose, banana, jute, etc., have also been used. From the above mentioned fibres, glass fibre is more advantageous on the basis of strength and fire resistant characteristics. It has been recognized that adding small, closely spaced and uniformly dispersed fibres to concrete serves to arrest cracks and improve its properties under static and dynamic loading. Round steel fibre is the most common variety in use for improving the tensile, flexural, impact and fatigue strength of concrete. The ductility and toughness of concrete are also improved with the addition of this fibres. Steel fibre have been used in various types of structures such as earthquake resistant structures, road overlays, airfield pavements and bridge decks. Alkali resistant glass fibre reinforcement is a relatively new addition to the family of fibres that impart high tensile strength, high stiffness, high chemical resistance and considerable durability to FRC (Fibre Reinforced Concrete). Adding polyesters fibre to concrete pavements resulted in the developments of the micro shrinkage cracks induced during hydration. These fibres improve the flexural strength and energy absorption of concrete . Glass fibres are useful because of their high ratio of surface area to weight. However, the increased surface area makes them much more susceptible to chemical attack. By trapping air within them, blocks of glass fibre makes good thermal insulation, with a thermal conductivity of order of 0.05 w/(mk). The strength of the glass fibre is usually tested and reported for virgin or pristine fibres those which have just been manufactured. The freshest and thinnest fibers are more ductile. The more the surface is scratched, the less the resulting tenacity. Because glass has an amorphous structure, its properties are the same along the fiber and across the fiber. Humidity is an important factor in the tensile strength. Moisture is easily absorbed, and can worsen microscopic cracks and surface defects, and lessen tenacity. Glass fibres improve the strength of the material by increasing the force required for deformation and improve the toughness by increasing the energy required for