composite materials -properties and uses
- 2. RCC • Reinforced cement concrete (R.C.C) is the combination of ordinary concrete with the reinforcement to increase its compressive and tensile strength to a great extent. • Concrete is a versatile material for modern construction which is prepared by mixing well-proportioned quantities of cement (even lime in some cases), sand, crushed rock or gravel, and water. • It has been used from foundations to the rooftops of buildings, in the construction of highways roads traffic, and hydro-power tunnels, irrigation canals, drains, and all other conceivable structures.
- 3. Purpose of Reinforcement in Concrete. • As you know that, Concrete has a very high compressive strength, but it is low in tensile strength. • Thus, when only the compressive loads are acting on the concrete surface, then there is no need of using reinforcement in it. • But where tensile forces are also involved, as in, beams and slabs, there is a very high risk of its failure when plain concrete is used. • Steel, however, as we know, has a very high tensile strength (and also have good compressive strength). • Hence, when these two (concrete and steel) are combined together, • a material of construction is obtained that is capable of withstanding all the three types of forces likely to act upon a structure, i.e., compressive loads, tensile stresses, and shear forces. • Such a material is known as Reinforced Cement Concrete.
- 4. Nature of Reinforced Cement Concrete: • The main principle in the preparation of the reinforced cement concrete is to make a structural material in which • (i) Steel serves the purpose of bearing the main tensile stresses; • (ii) concrete bears the main compressive forces, both acting in complete unison; • Concrete and steel are compatible in following aspects: • (i) Concrete is basically alkaline in nature, (the principal component being Calcium hydroxide) and this prevents rusting of the steel reinforcement used within it; • (ii) The bond or ‘grip’ between the steel and concrete is established easily; • (iii) The coefficient of thermal expansion of concrete is almost identical with that of steel.
- 5. Placement of Reinforcement: • it requires very complex and careful design considerations for each member of reinforcement concrete. • Thus, the size, shape, spacing, and location of reinforcement will be entirely different in a slab or beam or a column. • In beams, for example, steel bars may be required more in the lower sections and in fixed beams, in the end, sections as well where the tensile stresses are most effective. • The top section of the beam may need no reinforcement. • The horizontal reinforcements are often tied up with square stirrups at suitable intervals. • These stirrups also provide additional strength to the Reinforced Cement Concrete against shearing stresses. • The reinforcement requires the minimum prescribed covering of concrete. • The covering is essential to protect the reinforcement from deterioration under attack from weathering agencies and also from casual fires. • The concrete covering varies from 25 mm to 80 mm depending on the environment in which the RCC member has been placed. • It is also important that the reinforcement must be clear of rust, dust, and grease at the time of placement. • This will ensure a better bond between concrete and reinforcement.
- 6. Advantages of Reinforced Concrete (RCC). • (i) Structures made from Reinforced Concrete are durable. • (ii) It has a high compressive strength (due to concrete). • (iii) It has a high tensile strength (due to reinforcement). • (iv) It is resistant to fire and other climate changes. • (v) Easily available almost anywhere in the world. • (vi) Too much expertise is not required for working on it, normal skilled labor can also do it. • (vii) It can be molded in any form, shape. • (viii) It can be used in any part of the structure i.e., from foundation to the top roofing. • (ix) Repairing cost is almost nil. • (x) It is more economical compared to other materials.
- 7. Fiber-reinforced concrete (FRC) • Fiber-reinforced concrete (FRC) is concrete containing fibrous material which increases its structural integrity. It contains short discrete fibers that are uniformly distributed and randomly oriented. • It includes mixtures of cement, mortar or concrete and discontinuous, discrete, uniformly dispersed suitable fibers. Fibers are usually used in concrete to control cracking due to plastic shrinkage and to drying shrinkage. They also reduce the permeability of concrete and thus reduce the bleeding of water.
- 8. Benefits • Advantages of Fiber-reinforced concrete • Fibers reinforced concrete may be useful where high tensile strength and reduced cracking are desirable or when conventional reinforcement cannot be placed • It improves the impact strength of concrete, limits the crack growth and leads to a greater strain capacity of the composite material • For industrial projects, macro-synthetic fibers are used to improve concrete’s durability. Made from synthetic materials, these fibers are long and thick in size and may be used as a replacement for bar or fabric reinforcement • Adding fibers to the concrete will improve its freeze- thaw resistance and help keep the concrete strong and attractive for extended periods.
- 9. Benefits • Improve mix cohesion, improving pumpability over long distances • Increase resistance to plastic shrinkage during curing • Minimizes steel reinforcement requirements • Controls the crack widths tightly, thus improving durability • Reduces segregation and bleed-water • FRC, toughness is about 10 to 40 times that of plain concrete • The addition of fibers increases fatigue strength • Fibers increase the shear capacity of reinforced concrete beams
- 10. Different types of Fiber-reinforced concrete • Fibers for concrete are available in different sizes and shapes. The major factors affecting the characteristic of fiber-reinforced concrete are a water-cement ratio, percentage of fibers, diameter and length of fibers. Given below are different types of fiber-reinforced concrete used in construction.
- 11. Steel Fiber Reinforced Concrete • Steel fiber is a metal reinforcement. A certain amount of steel fiber in concrete can cause qualitative changes in concrete’s physical property. It can greatly increase resistance to cracking, impact, fatigue, and bending, tenacity, durability, and others. For improving long- term behavior, enhancing strength, toughness, and stress resistance, SFRC is being used in structures such as flooring, housing, precast, bridges, tunneling, heavy- duty pavement, and mining. The types of steel fibers are defined by ASTM A820 are, Type I: cold-drawn wire, Type II; cut sheet, Type III: melt-extracted, Type IV: mill cut and Type V: modified cold-drawn wire
- 12. Polypropylene Fiber Reinforced (PFR) Concrete • Polypropylene fiber reinforced concrete is also known as polypropene or PP. It is a synthetic fiber, transformed from propylene, and used in a variety of applications. These fibers are usually used in concrete to control cracking due to plastic shrinkage and drying shrinkage. They also reduce the permeability of concrete and thus reduce the bleeding of water. Polypropylene fiber belongs to the group of polyolefins and is partially crystalline and non-polar. It has similar properties as polyethylene, but it is harder and more heat resistant. It is a white rugged material with high chemical resistance. Polypropylene is manufactured from propylene gas in the presence of a catalyst such as titanium chloride. Polypropylene fiber displays good heat-insulating properties and is highly resistant to acids, alkalies, and organic solvents.
- 13. Glass Fiber Reinforced Concrete • Glass fiber reinforced concrete is a material consisting of numerous extremely fine fibers of glass. Glass fiber has roughly comparable mechanical properties to other fibers such as polymers and carbon fiber. Although not as rigid as carbon fiber, it is much cheaper and significantly less brittle when used in composites. Glass fibers are therefore used as a reinforcing agent for many polymer products; to form a very strong and relatively lightweight fiber-reinforced polymer (FRP) composite material called glass-reinforced plastic (GRP), also popularly known as “fiberglass”. This material contains little or no air or gas, is denser, and is a much poorer thermal insulator than is glass wool.
- 14. Polyester fibers • Polyester fibers are used in fiber-reinforced concrete for industrial and warehouse floors, pavements and overlays and precast products. Polyester micro- and macro-fibers are used in concrete to provide superior resistance to the formation of plastic shrinkage cracks versus welded wire fabric and to enhance toughness and the ability to deliver structural capacity when properly designed, respectively. Polyester micro- and macro-fibers are used in concrete to provide superior resistance to the formation of plastic shrinkage cracks versus welded wire fabric and to enhance toughness and the ability to deliver structural capacity when properly designed, respectively.
- 15. Carbon fibers • Carbon fibers are fibers about 5–10 micrometers in diameter and composed mostly of carbon atoms. Carbon fibers have several advantages including high stiffness, high tensile strength, low weight, high chemical resistance, high-temperature tolerance and low thermal expansion. Carbon fibers are usually combined with other materials to form a composite. When impregnated with a plastic resin and baked it forms carbon-fiber-reinforced polymer (often referred to as carbon fiber) which has a very high strength-to- weight ratio, and is extremely rigid although somewhat brittle. Carbon fibers are also composited with other materials, such as graphite, to form reinforced carbon composites, which have a very high heat tolerance.
- 16. Natural fibers • The natural fiber is directly obtainable from an animal, vegetable, or mineral source and convertible into nonwoven fabrics such as felt or paper or, after spinning into yarns, into woven cloth. A natural fiber may be further defined as an agglomeration of cells in which the diameter is negligible in comparison with the length. Although nature abounds in fibrous materials, especially cellulosic types such as cotton, wood, grains, and straw. The use of natural fibers in making concrete is recommended since several types of these fibers are available locally and are plentiful. The idea of using such fibers to improve the strength and durability of brittle materials is not new; for example, straw and horsehair are used to make bricks and plaster. Natural fibers are suitable for reinforcing concrete and are easily available in developing countries.
- 17. Application of Fiber-reinforced concrete • Runway • Aircraft Parking • Pavements • Tunnel Lining • Slope Stabilization • Thin Shell • Walls • Pipes • Manholes • Dams • Hydraulic Structure • Elevated decks • Roads • Bridges • Warehouse floors