What Is Fiber Reinforced Concrete?
Fiber reinforced concrete is Simple concrete that has very low tensile strength, limited ductility, and low resistance to cracking. Internal microcracks are inherent in the concrete and its poor tensile strength causes the dispersion of such microcracks, ultimately leading to fracture Concrete.
In the past, there have been attempts to improve the tensile properties of concrete members by using conventional reinforced steel bars and applying blocking techniques. Both methods provide tensile strength for concrete
Members, however, do not enhance the inherent tensile strength of concrete.
In simple concrete and similar stable materials, structural cracks (micro-cracks) develop even before loading, especially due to other causes of drying shrinkage or volume change. The width of these initial cracks may exceed a few microns, but their other two dimensions may be greater.
Advantages Or Uses Of Fiber Reinforced Concrete:
- Although every type of fiber is tried in cement and concrete, not all of them are used effectively and economically.
- Each type of fiber has its unique characteristics and limitations. Some fibers that can be used are steel fibers, polypropylene, nylons, asbestos, coir, glass, and carbon.
- Fiber is a small piece of reinforcing material that has some unique properties. They can be circular or flat. Fiber is usually described by a convenient parameter called “aspect ratio”. The aspect ratio of the fiber is proportional to the diameter of its length. The typical aspect ratio is 30 to 150.
- Steel fiber is one of the most commonly used fibers. Generally, rounded fibers are used. The diameter can vary from 0.25 to 0.75 mm. Steel fiber is corrosive and can lose some of its energy. But the investigation revealed that the corrosion of the strands only takes place on the surface.
- The use of steel fiber makes significant improvements in the flexibility, impact and strength of the concrete, which is widely used in a variety of structures, especially for surfaces of roads, airstrips, and bridge decks. Thin shells and plates are also constructed using steel fiber.
- Polypropylene and nylon fibers are found to be suitable for enhancing impact strength. They have very high tensile strength, but their low elasticity and high elongation do not lead to flexible strength.
- It is the most successful of all fibers as it can be mixed with asbestos mineral fiber and Portland cement. The tensile strength of asbestos varies between 560 and 980 N / mm2. The composite product, called asbestos cement, has substantially greater flexibility than Portland cement paste. For non-core fiber concrete, organic fibers such as choir, hemp, cane partitions are also used.
- Glass fiber is the latest introduction in the manufacture of fiber concrete. It has a tensile strength of 1020 to 4080 N / mm2. The glass fiber originally used in conjunction with cement was found to be influenced by the alkaline state of the cement. Therefore, the brand name “CEM-FIL” alkali-resistant glass fibers have been developed and used. Alkali-resistant fiber shows considerable improvement in reinforced concrete durability compared to conventional e-glass fiber.
- Carbon fibers perhaps possess very high tensile strength 2110 to 2815 N/mm2 and Young’s modulus. It has been reported that cement composite made with carbon fiber as reinforcement will have a very high modulus of elasticity and flexural strength. The limited studies have shown good durability. The use of carbon fibers for structures like cladding, panels, and shells will have a promising future.
Factors Effecting Properties of Fibre Reinforced Concrete:
- Relative Fibre Matrix Stiffness
- Volume of Fibres
- Aspect Ratio of the Fibre
- Orientation of Fibres
- Workability and Compaction of Concrete
- Size of Coarse Aggregate
- Fiber-reinforced concrete is increasingly used on account of the advantages of increased static and dynamic tensile strength, energy-absorbing characteristics, and better fatigue strength.
- The uniform dispersion of fibers throughout the concrete provides isotropic properties not common to conventionally reinforced concrete. Fiber-reinforced concrete has been tried on surfaces of air-grounds, road pavements, industrial floors, bridge decks, canal lining, explosive insulation structures, refractory lining, etc.
- The fiber-reinforced concrete can also be used for the fabrication of precast products like pipes, boats, beams, staircase steps, wall panels, roof panels, manhole covers, etc…
- Fiber-reinforced concrete sometimes called fibrous concrete is manufactured under the trade name “Wirand Concrete”. After extensive research, Wirand Concrete is widely used in the United States.
- Fiber-reinforced concrete is also being tried for the manufacture of “U” shaped preformed molds for casting lintels and small beams.
Different Types Of Fiber Reinforced Concrete:
1.Glass Fibre Reinforced Cement (GRC):
Glass-reinforced cement or cement is 4 to 4.5 percent by volume of glass fiber mixed in a sand mortar. This glass
Reinforced cement mortar is used to make concrete products 3 to 12 mm thick. The methods of preparation vary and are sprayed, casting, spinning, stripping, and pressing. Each technique gives different characteristics to the final product. Spray storage is the most suitable and most developed processing method.
In the simplest form of sprinkling, simultaneous sprays of cement or cement sand mortar and cut glass fiber are stored in a dual spray gun or in a suitable mold. The mortar slurry is fed to the spray gun by the metering pump unit and atomized by compressed air. The glass fibers are fed to the chopper and feeder unit embedded in the same gun assembly.
Glass-reinforced cement (GRC) is used for building cladding, permanent and temporary formwork, pressure pipes, doors, and door frames, decorative grills, sun breakers, bus shelters, and park benches. It can be used as building units in many applications.
Current Development in FRC:
The following are the three new developments taking place in FRC.
- High fiber volume micro-fiber systems.
- Slurry infiltrated fiber Concrete (SIFCON).
- Compact reinforced composites
- High Fibre Volume Micro-fibre Systems:
Micro-fibers are fibers generally of size about 3 mm long and 5 to 25 µ in cross-section in contrast to macro-fiber of length about 25 mm and a cross-section dimension of about 0.5 mm. The specific surface of micro-fibers is more than 200 cm2/gram in contrast to a specific surface of less than 20 cm2/gm.
Conventional mixing techniques and mix proportions usually lead to fiber balling, improper dispersion, and poor workability in micro-fiber cement with large volumes of fiber. Various innovative techniques of mixing in mixers called Omni mixer, use of admixtures such as carboxyl methylcellulose, Silica fume, and ground granulated blast furnace slag are practiced.
The System also requires large dosages of superplasticizers, low sand/cement ratio, longer mixing time, and sand particles of size not exceeding one mm.
- Slurry infiltrated fiber Concrete (SIFCON):
Slurry infiltrated fiber concrete (SIFCON) was invented by Lankard in 1979. The steel fiber bed is made and the cement slurry is infiltrated. With these techniques, micro-fiber contents up to about 20% by volume can be achieved, with a consequent enormous increase in both flexural loads carrying capacity and toughness.
With such high fiber volume, a very high compressive strength is also achieved. SIFCON can be used for explosion-proof structures and blower-resistant safe arches in banks and residential buildings.
- Compact reinforced composites:
Compact Reinforced Composites (CRC) is a material consisting of an extremely strong, dense cement matrix, 20 – 30% silica fume by weight of cement, 10 – 20% by volume off conventional reinforcement, and 5 – 10% of fine fibers of 6 mm long and 0.15 mm diameter.
While such material is extremely expensive, it exhibits a flexural strength of up to 260 MPa and compressive strength of about 200 MPa. It is a material almost as strong as structural steel. The advantage is that it can be molded and fabricated at the site.
Continuous research by concrete technicians to understand, improve and develop the properties of concrete has led to a new type of concrete called “polymer concrete”. It is mentioned time and again in previous chapters that concrete is porous. Porosity
Due to the inherent porosity of air voids, water voids, or gel formations.
Due to porosity, the strength of the concrete naturally decreases. It is conceived by many research workers that reduction of porosity results in an increase of the strength of concrete.
Therefore, processes like vibration, pressure application spinning, etc., have been practiced mainly to reduce porosity. All of these methods have been found to be very helpful, but none of these methods have really helped to reduce the inert porosity of the water volatiles and gel, which is estimated at about 28%.
Type of Polymer Concrete:
- Polymer Impregnated Concrete (PIC).
- Polymer Cement Concrete (PCC).
- And Polymer Concrete (PC).
- Partially Impregnated and surface coated polymer concrete
- Polymer Impregnated Concrete (PIC):
Polymer impregnated concrete is one of the widely used polymer composites. It is nothing but a precast conventional concrete, cured and dried in the oven, or by dielectric heating from which the air in the open cell is removed by vacuum. Then a low viscosity monomer is diffused through the open cell and polymerized by using radiation, application of heat, or by chemical initiation.
Mainly the following types of monomers are used:
(a) Methylmethacrylate (MMA),
(d) t-butyl styrene,
(e) Other thermoplastic monomers
- Polymer Cement Concrete (PCC):
Polymer cement concrete is made by mixing cement, aggregates, water, and monomer. Such plastic mixture is cast in molds, cured, dried, and polymerized.
The monomers that are used in PCC are:
(d) Vinylidene Chloride.
- Polymer Concrete (PC):
Polymer concrete is bonded to a polymer binder instead of Portland cement as conventional concrete. The main strategy in producing PC is to reduce the amount of void in the total mass, thereby reducing the amount of polymer needed to bind the aggregate. This can be achieved by properly grading and mixing the aggregates to obtain the maximum density and minimum void volume.
Stratified aggregates are prepackaged and vibrated in the mold. A monomer is dispersed by aggregation and polymerization is initiated by radiation or chemical means. A silane coupling agent is added to the monomer to increase the bond strength between the polymer and the aggregate. No polymerization is required if polyester resins are used.
- Partially Impregnated and surface coated polymer concrete:
In addition to the increase in strength, partial insertion is sufficient in cases where surface resistance against chemical and mechanical attacks is a key requirement. Even with partial insertion, a significant increase in the strength of the original concrete was obtained.
Initially, dried samples can be soaked in liquid monomers, such as methyl methacrylate, and partially inserted concrete, then covered with hot water to 70 ° C to prevent or minimize evaporation loss.
Application of Polymer Impregnated Concrete:
(a) Prefabricated structural elements.
(b) Prestressed concrete.
(c) Marine works.
(d) Desalination plants.
(e) Nuclear power plants.
(f ) Sewage works—pipe and disposal work.
(g) Ferrocement products.
(h) For waterproofing of structures.
(i) Industrial applications.
Carbon fibers are 5-10 micrometer diameter fibers and are mostly composed of carbon atoms. Carbon fibers have several uses, including high stiffness, high tensile strength, lightweight, high chemical resistance, high-temperature tolerance, and light thermal expansion.
They are usually combined with other materials to create composites. When filled and cooked with plastic resin it forms a carbon-fiber-reinforced polymer (often called a carbon fiber) that has a high strength-to-weight ratio, and is very tough, albeit a little flexible.
Carbon fibers are combined with other materials, such as graphite, to form reinforced carbon compounds, which have high heat tolerance.
4.Macro Synthetic Fiber:
Macro synthetic fibers are made from a mixture of polymers and were originally developed to provide an alternative to steel fibers in some applications. Initially, they were identified as potential alternatives to steel fibers in sprayed concrete, but increasing research and development have shown that ground-backed slabs can play a role in a wide range of applications.
They are particularly suitable for providing nominal reinforcement in invasive environments such as marine and coastal structures, as they do not suffer from stain and staining problems caused by steel corrosion. Moreover, because they are not run, they are used in the tram and light rail development.
Natural fibers are obtained directly from an animal, vegetable, or mineral source and also turned into non-woven fabrics such as felt or paper or woven into yarn. Natural fiber can be defined as the aggregation of cells in which the diameter is negligible compared to the length. While nature is abundant in fiber, especially cellulosic types such as cotton, wool, grains, and straw.
The use of natural fibers in the manufacture of concrete is recommended because many of these types of fibers are locally available and abundant. The idea of using such fibers to improve the strength and durability of stable materials is not new; For example, straw and horse chairs are used to make brick and plaster. Natural fibers are ideal for reinforcing concrete and are readily available in developing countries.
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