Portland Cement

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Engineering Chemistry

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Portland Cement :

Portland Cement Dr m e shelke Associate professor HVPM COET Amravati.

Portland Cement::

Portland Cement: Fine powder of mixture of Calcium Silicate & Calcium Aluminate of varying composition which on hydration (By adding Water & Drying) forms rigid structure having good compressive strength known as Portland Cement

Classification of Cement: :

Classification of Cement: Natural Cement Slag Cement Pozzolana Cement Portland Cement White Portland Cement Colour Portland Cement Rapid hardening Cement High Alumina Cement Low heat Cement Sulphate resisting Portland Cement

Raw material for manufacturing of Portland Cement: :

Raw material for manufacturing of Portland Cement: Calcareous material (Limestone [CaO], Chalk powder, Alkali wastes.) Argillaceous material (Alumina [Al 2 O 3 ], Silica [SiO 2 ], iron Oxide [Fe 2 O 3 ], Clay) Pulverised Coal or Fuel oil Gypsum ( CaSO 4 .2H 2 O)

Raw material for manufacturing of Portland Cement: :

Raw material for manufacturing of Portland Cement: Oxides % Lime [CaO] 60-67 Silica [SiO 2 ] 17-25 Alumina [Al 2 O 3 ] 3-8 Iron Oxide [Fe 2 O 3 ] 2-4 Magnesia [MgO] 1-5 Alkali Oxide { Soda Na 2 O& Potash K 2 O} 0.3-1.5 Sulphur Trioxide (SO 3 ) 1-3

Significance of Chemical Composition: :

Significance of Chemical Composition: Lime (CaO) :- Principal Constituents If excess or Lesser reduces Strength of cement Silica (SiO 2 ) :- Increases strength & Time of Setting. Alumina (Al 2 O 3 ) :- Increases strength & Decreases time of Setting. & If excess or lesser reduces Strength of cement

Significance of Chemical Composition::

Significance of Chemical Composition: Iron Oxide (Fe 2 O 3 ): - Provides gray colour to the Cement & also provides Strength & Hardness to Cement. Alkali Oxides :- Increases strength & If excess Causes the cement efflorescent. Sulphur Trioxide (SO 3 ): - Provides the Soundness. Magnesia (MgO): - Also provides the Soundness.

Methods of Manufacture of Portland Cement: :

Methods of Manufacture of Portland Cement: Dry Process: - Dry Mix. of raw material used Wet Process: - Slurry of raw material used

Dry Process :

Dry Process

Wet Process :

Wet Process

Construction & Working of Rotary Kiln :

Construction & Working of Rotary Kiln

Rotary Kiln:

Rotary Kiln

CEMENT SILO:

CEMENT SILO

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Drying Zone: - Upper part of the Kiln having Temp 100-500 0 C. Water Evaporates & Slurry gets dried (Endothermic) Pre heating Zone: - Upper Central part of the Kiln having Temp. 400-700 0 C. MgCO 3 Decompose MgO + CO 2 Calcining Zone: - Lower Central part of the Kiln having Temp. ranges from 700-1000 0 C. CaCO 3 Decompose CaO + CO 2

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Clinkering Zone: - Hottest zone having Temp. Ranges from 1400 - 1500 0 C. (Lime & Silica, Alumina reacts with each other to form Silicates & Aluminates) 2CaO + SiO 2 2CaO. SiO 2 ( Ca 2 SiO 3 ) i.e. C 2 S Dicalcium Silicates (25%) 3CaO + SiO 2 3CaO. SiO 2 ( Ca 3 SiO 3 ) i.e. C 3 S Tricalcium Silicates (45%) 3CaO + Al 2 O 3 3CaO. Al 2 O 3 (Ca 3 Al 2 O 4 ) i.e.C 3 A Tricalcium Aluminate (10%) 4CaO + Al 2 O 3 + Fe 2 O 3 4CaO. Al 2 O 3 .Fe 2 O 3 (C 4 AF) Tetracalcium alumino ferrite (10%) * Silicates + Aluminate = Cement Clinkers (Hard , Greyish) { Exothermic }

Cooling of Hot Clinkers :

Cooling of Hot Clinkers Cooling of Hot Clinkers: - Cooled in rotary steel cooler by atmospheric air. If rate of cooling of hot clinkers is Medium then Crystalline C 3 S is formed which provide more Binding prop. to the Cement . If slow , Then powdered C 2 S formed - Less Binding prop. to the Cement . If Fast , Then Crystalline C 3 A is formed & C 4 AF Prevented So, Rate of Cooling of Hot Clinkers must be MEDIUM

Additives for Cement :

Additives for Cement Accelerators: - It increases Initial strength of Cement Paste. If added more than 2% reduces Initial strength e.g. NaCl, CaCl 2 , Silicates. Retarders: - Reduces the Initial strength of Cement Paste. e.g. Gypsum (CaSO 4 .2H 2 O) Air Entrainment Materials: - Reduces the % of Entrapped air in Cement Concrete & also increases the durability of Concrete. e.g. Durex , natural Resins.

Additives for Cement :

Additives for Cement Water Repellants: - Reduces the moisture loving Characters of Portland Cement. e.g. Calcium & Aluminum Sterates . {Ca (C17H35COO) 2} Inert Fillers: - Reduces the Cost & Increases Strength of Cement. e.g. Sand , Limestone, Dolomite (Ore) Active Silica: - Increases the moisture resistance of Cement & also Increases Corrosive resistance due to Dissolved CO2 in Water. Workability Agents: - Decreases the heat of Hydration of Cement material. e.g. Slag , imestone , Talc, Ca(OH)2.

Properties of Constitutional Compounds :

Properties of Constitutional Compounds {Cement + Water = undergo Hydration at diff. Rates} Tricalcium Silicates (C 3 S): - Rate of Hydration is Medium. & Develops very high early strength. Heat of Hydration is 502 KJ/Kg Dicalcium Silicates (C 3 S): - Rate of Hydration is slow. & Develops low early strength but develop Overall Strength. Heat of Hydration is 251 KJ/Kg (Lowest) Tricalcium Aluminate (C 3 A): - Early strength is good but overall strength is low. Heat of Hydration is 880 KJ/Kg Tetracalcium alumino ferrite (C 4 AF): - Rate of Hydration is low. Both early & overall strength is poor so, It's Heat of Hydration is 418 KJ/Kg

Setting & Hardening of Portland Cement :

Setting & Hardening of Portland Cement Water + Cement = Plastic mass( Cement Paste) Forms Rigid Structure in setting time Kn /as Initial or Flash Time Then after some days final Setting & Hardening of Cement takes place due to Hydration & Hydrolysis reaction.

Setting & Hardening of Portland Cement :

Setting & Hardening of Portland Cement Initial Setting of Cement Paste:- Due to Hydration of C 3 A & Hydration of C 4 AF *3CaO. Al 2 O 3 + 6 H 2 O 3CaO. Al 2 O 3 . 6 H 2 O(Ca 3 Al 2 O 4 ) (Cubic) Crystalline gel *3CaO. Al 2 O 3 + 12 H 2 O 3CaO. Al 2 O 3 . 12 H 2 O (Ca 3 Al 2 O 4 ) (Hexagonal) Crystalline gel *3CaO. Al 2 O 3 + 17 H 2 O 3CaO. Al 2 O 3 . 17H 2 O (Ca 3 Al 2 O 4 ) (Rhombic) Crystalline gel C 4 AF + 6 H 2 O C 3 A . 6 H 2 O + CFH 2 O (Cubic) Calcium ferrite gel ** These Hydrates are Soluble ,hence provide Stiffness.

Setting & Hardening of Portland Cement :

Setting & Hardening of Portland Cement Final Setting & hardness of Cement Paste:- Due to i ) Hydrolysis of C 3 S to form C 2 S 2 gel & Crystalline Ca(OH) 2 & ii) Hydrolysis of C 2 S to form C 3 S 2 gel 2C 3 S + 6 H 2 O + O 2 hydro. C 3 S 2 . 3H 2 O + 3 Ca(OH) 2 28 Tri cal. Disilicate (Crystalline) (Gel) 2C 2 S + 4 H 2 O + O hydro. C 3 S 2 . 3H 2 O + Ca(OH) 2 28 Tri cal. Disilicate (Crystalline) (Gel)

Setting & Hardening of Portland Cement :

Setting & Hardening of Portland Cement

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Uses Main use is in the fabrication of concrete and mortars Modern uses Building (floors, beams, columns, roofing, piles, bricks, mortar, panels, plaster) Transport (roads, pathways, crossings, bridges, viaducts, tunnels, parking, etc.) Water (pipes, drains, canals, dams, tanks, pools, etc.) Civil (piers, docks, retaining walls, silos, warehousing, poles, pylons, fencing) Agriculture (buildings, processing, housing, irrigation) USES

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