06-10-2016, 10:25 AM
STRENGTH AND DURABILITY PROPERTIES OF HYBRID FIBRE REINFORCED CONCRETE – AN EXPERIMENTAL STUDY
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ABSTRACT:
Concrete is most widely used construction material, concrete possesses a very low tensile strength, limited ductility and limited resistance to cracking. Concrete is non - durable when it is subjected to highly aggressive environment. The strength and durability properties of concrete can be increased by addition of fibre. Concrete reinforced with single fibre may improve the desired properties to a limited level. Concrete reinforced with two or more fibre that derives the benefits from each of the individual fibre. The combining of fibre, often called hybridization.
Steel and polypropylene fibre as an addition to concrete to make it as a hybrid fibre reinforced concrete. Steel and polypropylene fibres have different properties, steel fibre is to increase the strength parameters and polypropylene fibre resists the initial crack, shrinkage and improves durability properties.Specimens are cast using M30 grade concrete. The specimens are incorporated 1% and 0.1% volume fraction of steel and polypropylene fibre respectively.Mechanical properties such as compressive strength, split tensile strength, flexural strength and durability properties are determined for both conventional concrete and hybrid fiber reinforced concrete specimen.
INTRODUCTION
Concrete is an artificial material, which has wider application in construction industry. Concrete is a brittle material that perform well in compression, but it is considerably less effective when in tension.Conventional concrete has limited ductility, low impact resistance and abrasion resistance, little resistance to crackingand so on that restrict it application. The cracking of concrete may due to structural and environmental factor, but most of the cracks are formed due to inherent internal micro cracks, thereby impairing the water proofing properties and exposing the interior of the concrete to the destructive substances containing moisture, acid, sulphate etc.. The exposure acts to deteriorate the concrete, with the reinforcing steel corrosion. To overcome these deficiencies extra materials are added to improve the performance of concrete.
Fibre reinforced concrete provides solution for this problem. The concrete containing cement, water, aggregate and discontinuous discrete fibres is called “Fibre Reinforced Concrete”. Generally, the length and diameter of the fibres used for FRC do not exceed 76mm and 1mm respectively. Brittle materials are considered to have no significant post – cracking ductility. When subjected to tension, these unreinforced brittle matrices initially deform elastically. The elastic response is followed by micro cracking, localized macro cracking, andfinally fracture. Introduction of fibers into the concrete results in post-elasticproperty changes that range from subtle to substantial, depending upon anumber of factors, including matrix strength, fiber type, fiber modulus, fiberaspect ratio, fiber strength, fiber surface bonding characteristics, fiber content,fiber orientation, and aggregate size effects.
Reinforcement with single fibre may improve the desired properties to a limited level. For optimal result different type of fiber may be combined and resulting composite may known as Hybrid Fibre Reinforced concrete. The use of optimized combination of two or more type of fibres in the same concrete mixture can produce a composite with better engineering properties than that of individual fibres. Hybridization of fibre provide a system in which one type of fibre which is stronger and stiffer improves the first crack stress and ultimate strength and second type of fibre which is more flexible and ductile leads to the improved toughness and strain capacity in the post cracking zone. This project work focus on steel – polypropylene fibre reinforced system.
II. Literature Review
Perumal. Pet al (2010) evaluated the seismic performance of hybrid fiber reinforced beam – column joint. In this research effect of different proportion of hybrid fiber combination (1.5% of steel fiber and 0 to 0.4% of polypropylene fiber) at the joint of exterior beam – column joint connection subjected to earthquake loading using M60 grade concrete. Fly ash and silica fume are used to cast the specimens. They concluded that the HFRC joints undergo large deflection without developing wider cracks when compared to HPC joints. The addition of polypropylene fiber increases the energy absorption capacity, ultimate load. It is possible to reduce the steel reinforcement in beam column joint by replacing the steel and synthetic fiber. The hybrid fiber combinations of 1.5% of steel and 0.2% of polypropylene fiber have best performance.
Patel. A et al (2012) evaluated the engineering properties for polypropylene fiber reinforced concrete. An experimental investigation explored properties such as compressive strength, flexural strength, split tensile strength, shear strength of polypropylene fiber reinforced concrete. The fiber volume fraction ranges from (Vf) 0 to 2%. The result shows that the presences of fiber in concrete alter the failure mode of material. It is found that the failure mode of plain concrete is mainly due to spalling , while the failure mode of fiber concrete is bulging in transverse direction.
Kulkarni. C.V et al (2012) studied the performance evaluation of hybrid fiber reinforced concrete matrix. Recron 3S fiber and continuously crimped steel fibers are used to produce hybrid fiber reinforced concrete. Samples were prepared with and without fly ash and by varying the volume fraction of fibers from 0% to 1% different types of HFRC matrices were prepared. It was concluded that matrix having 1% volume of steel fiber indicate the increase in compressive strength. The combined behaviour of RS37 matrix found more balanced in terms of strength and ductility.
Rajarajeshwari. B Vibhuti et al (2013) conducted a study on mechanical properties of hybrid fiber reinforced concrete for pavements. In this study addition of mono fiber and hybrid on the mechanical properties of concrete mixture studied. Steel fiber 1% polypropylene fiber 0.036% were add individually to the concrete mixtures as mono fibers and then they were added together to form HFRC. Compressive, flexural and split tensile strength of the concrete specimen were studied. Finally they concluded hybridization of fiber improve the mechanical properties of fiber. The improved mechanical properties of HFRC would result in reduction of wrapping stress, short and long term cracking.