Influence of minor elements

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Influence of minor elements

 

Free lime

o It is the lime which is not combined to other elements. This CaO in too large amount brings expansion. A too low content is a sign of an over burnt clinker which is going to be much less reactive.

o The optimum is around 1%

Free lime and setting time reduction

Magnesia

o It is also dangerous in too large amount because it leads to expansion and cracks

Influence of alkalies

Definitions

« the alkalies which are in the cement come from the raw materials. They are Sodium and Potassium »

o Soluble

it is the fraction which is associated with the sulphate coming from the raw materials or from the fuels

o Insoluble

it is the fraction which is not combined with the sulphates. The alkalies enter into the cristals of silicates or aluminates

Total

it is the sum of both Soluble and Insoluble

Where are the alkalies to be found in clinker

A pinch of alkalies and… … strength falls

Increasing the soluble alkalies increases the early strength

Other minor elements

P2O5

< 0,5% of clinker: no action

  > 0,5% of clinker increase C2S and free   Cao make the burning more difficult with a   decrease in early strength and an increase   of setting time

Zn

< 0,5% of clinker: no incident

  > 0,5% setting time and strength are   retarded

Cl

dangerous for the dry process, it increases the early strength

 

 

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