Cement Manufacture, Nomenclature And Composition

Question 1

What is C3S?

Answer 1

Tricalcium silicate, Alite. Main phase of Portland cement clinker. 40-60%. Fast hydration. High contribution to strength.

Question 2

What is C2S?

Answer 2

Dicalcium silicate, Belite. Phase in Portland cement. 10-25%. Slow rate of hydration. High contribution to strength.

Question 3

What is C3A?

Answer 3

Tricalcium aluminate. Phase in Portland cement. 10-15%. Fast hydration. Can cause flash set and poor sulphate resistance. Alumina acts as flux to help form silicates. Low contribution to strength.

Question 4

What is C4AF?

Answer 4

Tetracalcium aluminoferrite. Phase of Portland cement. 10-15%. Slow rate of hydration. Low contribution to strength. Contains lots of impurities.

Question 5

How does increasing the temperature of a kiln affect the early age strength of Portland cement?

Answer 5

Increasing the temperature produces more Alite which is high strength and therefore increases the strength of the cement.

Question 6

What are the raw materials used in cement production?

Answer 6

Limestone

Clay, shale, mudstone

Minor constituents

Question 7

Describe CEM 1 Portland cement manufacture

Answer 7

1. Limestone and clay mixed in correct proportions.
   2a. Preheat to dry and decarbonate CaCO3
   b. Kiln at 1450C to form clinker, then cooled rapidly to freeze defects in the structure making the material more reactive
2. Grind clinker to a powder, then package

Question 8

Why is the drying process preferred over the wet process in cement manufacturing?

Answer 8

The wet process is easier for processing, intimate mix of calcium and clays but requires more energy.

Question 9

How does the extent of grinding affect the properties of cement?

Answer 9

More grinding, more reactive cement

Question 10

Why is calcium sulphate added to clinker?

Answer 10

Inhibits flash set and is a grinding aid.

Question 11

What is the purpose of ground limestone in cement?

Answer 11

Acts as a filler but also slightly reacts with aluminium phases.

Question 12

Why is ferrous or stannous sulphate added to cement?

Answer 12

Reduces Cr(VI), which causes cancer and dermatitis, to Cr(III), which doesn’t cause cancer. Also produces a shelf life of 6 months, as Cr(III) will slowly re-oxide to Cr(VI).

Question 13

How many tons of raw material are needed to produce 1 ton of cement?

Answer 13

1.6 tons

Question 14

Which stage of cement manufacturing process results in direct CO2 emission and how much is produced per ton of cement?

Answer 14

Preheating, conversion of limestone to CaO + CO2 @600C

0.6-0.8 tons produced