August 8, 2020

Chemical composition of Cement & Bogue’s Compound

Cement

Cement is a material which has cohesive & adhesive properties in the presence of water. It was invented by Joseph Aspdin of UK in 1824 & its colour resemblance to strom found in Portland (England). So it is called Portland cement.John Smeaton is considered as father of civil engineering. In this post you will get information about chemical composition of Cement & Bogue’s Compound.

Basic calculation about cement volume is given as follow :

Standard Density = 1440 Kg/m3

Weight of 1 bag of cement = 50 Kg

Volume = 50/1440 = 0.0347 m3

The tolerance in measurement of cement is 2% positive and negative. Impart more strength.

Unit weight of various materials in Kn/m3

  1. Brick Masonry : 19-20
  2. Plain cement concrete : 22-24
  3. Reinforced cement concrete : 24-25
  4. Cement Mortar : 20-21
  5. Steel : 78-80
  6. Cement : 14.4

Cement is having 2 types of classification given below :

There are 2 types of raw materials use in cement manufacturing which are Argillaceous and calcareous.

ArgillaceousCalcareous
Blast furnace SlagLime stone
Cement RockChalk
MarlMarine Shells
Shale and clay 

Chemical composition of Raw Materials

OxideComposition %AvgFunction
Lime (CaO)60-6562Deficiency reduce strength & setting action
Silica (Sio2)17-2522Excess of it cause slaw setting
Alumina (Al2O3)3-86Responsible for quick setting , excess of it lower strength (No contribution in strength)
Iron Oxide (Fe2O3)0.5-63Gives colour & help in fusion of different ingredients of cement colour & hardness
Magnesia (MgO)0.1-42Colour & hardness
Soda & Potash (Na2O)0.5-1.31If in excess cause efflorescence & K2O ) Cracking
Sulphur Trioxide SO31-31.5Makes cement Sound

Cement Storage

  1. Floor area occupied by a cement bag in warehouse is 0.3 m2 & heights is 0.18 m.
  2. The length of one bag of cement is 0.70 m.
  3. The width of one bag of cement is 0.42 m.
  4. It must be kept above from the ground level about 45 cm.
  5. The distance of cement bag from the wall should be 30 cm.
  6. As per IS 4082:1996 the stacking & storage of cement shall be done as follows :
  7. It shall be stored at the worksite in building or a shed which is dry, leakproof & moisture proof as possible.
  8. The bags shall be staked off the floor in godown on the wooden piles in such a way that as to keep about 150 mm to 200 mmc clear above the floor.
  9. A space of 600 mm minimum shall be left around between the exterior walls & the stack.
  10. The height od stack shall not be more than 10 bags to prevent the possibility of lumping up under pressure.
  11. The width od stack not be more than four bags length or 3 meters
  12. In stack more than 8 bags high the cement bags shall be arranged alternatively lengthwise & crosswise so as to tie the stack together & minimize the danger of topping over.
  13. The bags shall be stacked in manner to facilitate their removal & use in order in which they are received, a label showing date of receipt of cement shall be put on each stack to know the age of cement.
Period of storage% Strength at 28 days of concrete
Fresh100
3 months80
6 months70
12 months60
24 months50

Bogue’s Compound

When these raw materials are put in kiln. Then it fuses & following four major compounds are formed. It is very important to understand the Chemical composition of Cement & Bogue’s Compound.

Principal MethodCompoundFormulaAvgSymbol Function
Tri calcium silicate (Alite)3CaO.SiO2C3S40%7-Days strength & hardness, best cementing material (Resistance to the freezing, thawing)
Dicalcium Silicate (Belite)2CaO.SiO2C2S32%Ultimate strength (1 Year Strength)
Tri calcium Aluminate (Celite)3CaO.Al2O3C3A10%Flash Set, Initial setting
Tetra Calcium Alumina ferrite (Felite)4CaO.Al2O3.Fe2O3C4AF8%Poorest Cementing value

It is found that ordinary Portland cement achieves 70% of its final strength in 28 days & about 90% in one year but for design purpose we take 28 days strength as 100%

Flash Set

It is the stiffening of cement paste without strength development with heat evolution which also called premature hardening. It is cause by C3A high alkali. Tricalcium aluminate react immediately with water & its responsible for flash set.

  • Gypsum Is added to cement to reduce flash setting.
  • After flash set mixing is not allowed because no gain in strength developed after mixing.
  • Gypsum retards setting time of cement
  • It is usually mixed with clinker at the time of final grinding.
  • Gypsum retards setting time of cement
  • Gypsum is usually mixed with clinker at the time of final grinding. Excess gypsum makes cement unsound. So gypsum added to clinker should not be greater than 2.5 to 3%.
  • Water requirement for hydration.

Hydration of cement is an exothermic reaction. Bound water 23% by weight of cement and Gel water 15% by weight of cement thus total 38% of water is required.

Rate of Hydration C4AF > C3A > C3S > C2S

Rate of heat evolution C3A > C3S > C4AF > C2S

Normal amount of water use to mix each 50Kg bag of cement is in range 20-30 litres. For ordinary Portland cement it is 27 liter/bag for PPC it is 25 liter/Bag at W/C 0.45.

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