10 secrets of clinker

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10 secrets of clinker

First Rule

Reducing raw mix rejects lowers burning temperature and grinding energy. This is particularly the case with siliceous rejects.

This action is also beneficial to strength properties.

Key Figures:

When the amount of 100µm rejects is reduced from 20 to 10%, the global raw mix cement energy consumption is lowered by about 4 kWh per tonne of cement at a fineness of 350 m2/kg.

Grind the raw mix finer

You will save on

  • Fuel at burning
  • kW at finish grinding

Finer raw mix = Fuel saving


Finer raw mix = Fuel saving

Finer raw mix = Fuel saving

Finer raw mix = kw at raw mill

Finer raw mix = kW savings at finish grinding

Finer raw mix = kW savings at finish grinding

Second rule

A short profile promotes grindability and strength


Key Figures :

The optimum is achieved when the kiln torque is at the minimum value compatible with stable kiln operation.

A hot and short burning zone

Gives easy grinding clinker

Shorter burning zone: better grindability

Third rule

Steady production requires an oxidizing atmosphere because a reducing atmosphere increases volatilization, causing both “ cyclical ” operations and sulfate and alkali fluctuations, hence producing an irregular clinker.

Give the kiln a breath of fresh air

A big reduction in volatilization

With, in addition,

* Steady kiln operation

* Stable clinker quality

Oxygen  and Sulfates  Volatility

Fourth rule

Increasing the clinker free lime content reduces both initial and final

setting times in the same proportion.

Adding lime also accelerates both initial and final setting times.

Key figures :

When free CaO increases from 0.5 to 1.5%, initial set decreases by

about 40 to 50 minutes. This impact may vary greatly from clinker

to clinker (-10 to -100 minutes).

 Lime quality (specifically the burning temperature, its degree of

hydration etc.) and clinker quality have an influence on the results


Add a pinch of free-lime Your clinker will be quicker – Shorter initial setting time

Free lime and setting time reduction

Limestone injection  BATH kiln outlet

Limestone injection at the cooler

Fifth rule

Increasing clinker C3S (to the detriment of C2S) improves strength at 1, 2, 3 and 7 days. After 28 days, the gain may be less because of the C2S contribution.

Key figures :

+10% C3S  >>  +2 to +5 MPa   for early strengths

Strengths = f(C3S)  

Sixth Rule

For a given Blaine specific surface (SSB), grinding energy increases with C2S content. Conversely, it decreases with increasing  C3S.

Key figures :

+10% C2S, (or -10% C3S) => +5 kWh/t (@ 3500 cm2/g).

Grindability = f( chemistry)

Seventh rule

Alkalies, whatever their form, are never favorable to 28-day

compressive strength.

Key figures :

+ 0.1 % Eq Na2O total >= -1 N/mm2 at 28 days

Influence of Total Alkalies   on 28-day strength

Strength = f (alkalies)

Eighth rule

At optimum sulfate addition for early ages, soluble alkalies, especially alkali sulfates, improve early strength.

Key figures :

+ 0.1 % Eq. Na2O soluble –> + 0.5 à 1.5 N/mm2 @1 day

Sulfate increase

Alkalie increase

Ninth rule

The molar saturation of alkalies by SO3 in the clinker facilitates workability control

Gypsum addition in raw meal    (lab test)

Gypsum addition in raw mix    ( Industrial tests)

Tenth rule

If clinker SO3 is increased beyond the molar saturation of alkalies, an increase in both clinker fineness and grinding energy is noted.

Key figures :

+1% Excess SO3 –> + 5 kWh/t @ 350 m2/kg

excess SO3 = SO3 clinker – 1,29 (% Eq. Na2O total)

EXCESS  of  Sulfates


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