CEMENT,PCC ,RCC ,PSC

CEMENT     Cement is manufactured by calcifying calcarious material (lime) and argillaceous material (shale  and clay) and then clinker so formed is ground to fine powder. Use of cement alone is limited to  filling small cracks with its paste. It is mainly used as binding material in mortar and concrete. PLAIN CEMENT CONCRETE The intimate mixture of cement, sand, coarse aggregate (jelly) and water is known as plain cement concrete. A small quantities of admixtures like air entraining agents, water proofing agents, workability agents may also be added to impart special properties to the plain cement concrete. Uses of plain cement concrete is listed below: 1. As bed concrete below the wall footings, column footings and on walls below beams. 2. As   sill concrete to get a hard and even surface at window and ventilator sills. 3. As coping concrete over the parapet and compound walls. 4. For flagging the area around the buildings. 5. For making pavements. 6. For making tennis courts, basket ball courts etc.         REINFORCED CEMENT CONCRETE     Concrete is good in resisting compressive stress but is very weak in resiting tensile stresses. Hence reinforcement is provided in the concrete wherever tensile stress is expected. The best reinforcing material is steel, since its tensile strength is high and bond between steel and concrete is good. Since elastic modulus of steel is quite high compared to concrete, the force developed in steel is high. A cage of reinforcements is prepared as per the design requirements, kept in the form work and then green concrete is poured. After the concrete hardens, the form work is removed. The composite material of steel and concrete, now called R.C.C. acts as a structuralmember and can resist tensile as well as compressive forces efficiently. Uses of R.C.C. 1. R.C.C. is used as a structural member wherever bending of the member is expected. The common structural elements in a building where R.C.C. is used are: (a) Footing (b) Columns (c)  Beams, lintels (d)  Chejjas, roof slabs (e)  Stairs. 2. R.C.C. is used for the construction of storage structures like: (a)  Water tanks (b)  Dams (c)  Silos, bunkers 3. They are used for the construction of (a)  Bridges (b)  Retaining walls (c)  Docks and harbours (d)  Under water structures 4. R.C.C. is used for building tall structures like (a)  Multistorey buildings (b)  Chimneys (c)  Towers. 5. R.C.C. is used for paving (a)  High ways (b)  City roads (c)  Airports. 6.R.C.C. is used in atomic plants to prevent radiation. For this purpose R.C.C. walls built are as thick as 1.5 m to 2.0 m. PRESTRESSED CONCRETE (PSC)     In prestressed concrete elements, calculated compressive stresses are introduced in the zone  wherever tensile stresses are expected when the element is put to use. Thus in bridge girders, bottom side of beam tensile stresses develop when deck slab is placed and vehicles start moving on the bridge. Hence before girder is placed in its position compressive stresses are introduced at bottom side. This is achieved by pulling the high tensile wires before concrete is poured in the form work of beam and releasing the pull only after concrete hardens (pretensioned prestress concrete). In another method, it may be achieved by providing a duct from end to end in the beam while casting the beam. Then high tensile wire is passed through the duct and after stretching, it is anchored to the ends of beams. This is called post-tensioning prestress beam. ACI committee defines prestressed concrete as the one in which internal stresses have been introduced such that the stresses resulting from given external loadings are counter-acted to a desired degree. Prestressed concrete is commonly used in making the following structural elements. 1. Beams and girders. 2. Slabs and grid floors. 3. Pipes and tanks 4. Poles, piles, sleepers and pavements. 5. Shell and folded plate roofs. PRECAST CONCRETE     Usually concrete structures are built by casting them in their final position in the site by providing form work, pouring concrete and then removing the form work. It is called as cast-in-situ construction. If concrete elements are cast in factories or elsewhere and transported to their final destination, they are called precast elements. Since the elements are cast in factories where controls are better, they are superior to cast in situ elements. However, the disadvantage is cost of transportation and achieving desired connections on site. Precast concrete is used in the following: 1. Pipes and tanks 2. Poles, piles, sleepers and pavement 3. Lintel beams 4. Beams and girders 5. Building blocks 6. Wall panels 7. Manhole covers