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by Amity Kumar
Type: NoteInstitute: Amity University Specialization: Civil EngineeringDownloads: 65Views: 1973Uploaded: 7 months agoAdd to Favourite

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Concrete Technology Definition: Cement is defined in many ways as follows, • Cement, any material that hardens and becomes strongly adhesive after application. • Manufactured substance consisting of gypsum plaster, or Portland cement. • Portland cement hardens and adheres after being mixed with water. History of Cement: • The term “Portland cement” was first used in 1824 by Joseph Aspdin, a British cement-maker, because of the resemblance between concrete made from his cement and Portland stone, which was commonly used in buildings in Britain. • At that time cements were usually made in upright kilns where the raw materials were spread between layers of coke, which was then burnt. • The first rotary kilns were introduced about 1880. Portland cement is now almost universally used for structural concrete. Manufacturing Process: • Main ingredients used in the manufacture of cement are: • Limestone – Calcium • Clay, shale – Silica/Alumina • Quarrying – local resources necessary: no market • Limestone (CaCO3) and Clay are two main raw materials used for manufacturing Portland cement clinker. • Clays have various amount of SiO2 and Al2O3. • In the manufacturing process of Portland cement, clinker consist essentially of grinding the raw materials, mixing them in appropriate proportion, burning the raw material in a kiln at a temperature of 1400-1500oC until material partially fuses into balls known as Clinker and grinding cooled clinker together with a small amount of gypsum rock. • The mixture of raw material is burned in a rotary kiln. THE KILN The heart of the cement plant • Largest moving part of any machine. • inclined, rotates. • up to 50m long and 5m diam. 1
• • • • • • • • • • • • • • • Heated by fire jet The rotary kiln is along steel cylinder lined with refractory brick (length /diameter ~30). Modern kilns may reach 6m in diameter and over 180m in height with a production capacity exceeding 1000 tones a day. The kiln is inclined a few degrees from the horizontal ( about 4 cm\m ) and is rotated about its axis at a speed of about 60 to 150 revolution\hour ). Pulverized coal or gas is used as the source of heat. The heat is supplied from the lower end of the kiln. The max. temperature near the lower end of the kiln is generally about 1400-1500 OC. The upper end of the kiln the temperature is around 150 OC. The mixture of the raw material is fed from the upper end of the kiln.This material move toward the lower end by effect of inclanation and rotation of the kiln. Thus the materials are subjected to high temperature at lower end of the kiln. The materials that are introduced into the rotary kiln are subjected to several distinct process as they move downward. When the raw materials are fed into the kiln, drying of the material takes place, and any free water in the raw material is evaporated. Clay losses its water about 150 to 350 OC. Clay decompose at a range of 350 to 650 OC. Magnesite in raw material loss about 600 OC. The limestone losses its CO2 at about 900 OC. At 1250 to 1280 OC some liquid formation begins and compound formation start to takes place. Clinkering begins at about 1280OC. The liquid that forms during the burning process causes the charge to agglomerate into nodules of various size, usually 1 - 25 mm in diameter known as Portland cement clinker. All exhaust gases produced during the burning process of the materials leave the kiln through the stack. 2
COOLING & GRINDING • Rapid cool - glassy • Grinding – Starts at golf ball size – ends about 2-80 microns, 300 m2/kg – depends on application • Typical plant: 1 MT/y • Portland cement is manufactured by inter grinding the portland cement clinker with some (3 to 6 %) Gypsum rock. QUANTITIES • Worldwide: ~2 GT/y – China: 860 MT/y US: 100 MT/y – India: 200 MT/y UK: 12 MT/y • CONCRETE: ~15 GT/y – cf. steel ~1 GT/y, wheat ~0.6 GT/y, rice ~0.4 GT/y – 2.5 T for each of us! – 2mm Earth surface ECONOMIC IMPORTANCE • Availability & price crucial to national development – Cement: 1-2% of total construction costs – Construction: 5-10% of GDP – Demand for cement is key economic indicator APPLICATIONS • Structural – Reinforced concrete • Structuro-functional – bone/dental cements • Functional – waste immobilisation, land remediation • Sculptural • Improbable CONCRETE Concrete is a mixture of Cement paste and aggregate • Compression: up to 120 MPa – Comparable to Al • Tension: <10 MPa • Tension reinforcement – steel bars 4

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