Cement Raw-Mix

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Cement is a mixture of calcium silicates and smaller amounts of Tetra-calcium alumino-ferrite & calcium aluminates that react with water and cause the cement to set The requirement for calcium is met by using high calcium limestone (or its equivalent calcareous raw material) and clay as the source of most of the silica, alumina & Iron. Finished cement is produced by finely grinding together around 95% cement clinker with 5% gypsum (or anhydrite) which helps to retard the setting time of the cement.

The quality of cement clinker is directly related to the chemistry of the raw materials used. Around 80–90% of raw material for the kiln feed is limestone. Clayey raw material accounts between 10–15%, although the precise amounts will vary and Iron ore raw material account between 1-2 %. Magnesium carbonate, which may be present in limestone, is the main undesirable impurity. The level of magnesia (MgO) in the clinker should not exceed 5% and many producers favor a maximum of 3%; this rules out dolomite or dolomitic limestones for cement manufacture. Other deleterious materials include excessive alkalis (sodium oxide, Na2O or soda and potassium oxide, K2O) which would be unacceptable because of durability problems with the concrete (due to the reaction of alkalis with some siliceous aggregates to form a swelling gel; a jelly-like substance that increases in volume with adverse effects on cement durability and strength.(1)

Cement Raw-Mix

The raw materials mixture is called Raw-mix or Raw-Meal or Kiln feed, which is characterized:

  1. Chemically according to chemical composition.
  2. Physically according to particle size and shape, particle size distribution & homogeneity.
  3. Mineralogical morphology according to crystal size, and mineral & crystal distribution.

According to raw materials chemical composition raw-mix is designed to achieve sufficient clinker minerals’ content and smooth kiln operation. Mostly the following modules are implemented:


1- Alumina Ratio (AR) (2)

This determines the potential relative proportions of aluminate and ferrite phase in the clinker. An increase in clinker AR means there will be proportionally more aluminate and less ferrite in the clinker, in addition to characterizes the composition of the melt and its viscosity in the clinker; low AR <1.5 increases the Fe2O3 content, decrease the viscosity and increase infiltration of the liquid, deep into the bricks(refractory). In ordinary Portland cement clinker, the AR is usually between 1 and 4.


Effect of high AR

  1. Imparts harder burning & entail high fuel consumption
  2. Increase the C3A & Reduce C4AF contents
  3. Increases both C3S & C2S (C3S > C2S)
  4. Reduces the liquid phase in kiln outpeal
  5. Trends to render quick setting and strong in early ages
  6. Increases viscosity of liquid phase in rawmix

AR determines the flux in raw-mix; if < 1.23 Al2O3 act as flux, if > 1.23 Fe2O3 act as flux.

If AR is too low and raw-mix is without free silica clinker sticking & balling is high.

2- Silica Ratio (SR) (3)

A high silica ratio means that more calcium silicates are present in the clinker and less aluminate and ferrite in addition to characterizes the ratio solid/liquid the amount of liquid phase in the clinker. SR is typically between 2.0 and 3.0.

Effects of high SR:

  1. Harder burning
  2. Higher fuel consumption
  3. Causes unsoundness
  4. Difficulty coating formation
  5. Deterios kiln lining
  6. Slow setting and hardening of cement

Effect of low SR:

  1. Increases liquid phases
  2. Improves burnability of clinker and formation of coating in kiln 

3- Lime Saturation Factor (LSF):

The LSF is a ratio of CaO to the other three main oxides, a clinker with a higher LSF will have a higher proportion of Alite to Belite than will a clinker with a low LSF. There are several formulas to calculate LSF as per the following:

The impacts of high LSF (> 0.95) are:

  1. Harder to burn
  2. Tendency to high F.CaO & C3S Clinker
  3. Causes slow setting with high strength of cement
  4. High fuel consumption
  5. Tends to produce unsound cement
  6. Improves grindability characteristic of clinker.


The impacts of low LSF (< 0.95)

  1. Easy to burn
  2. Excess coating
  3. Excess liquid phase
  4. Possible bricks infiltration
  5. Reduced cement strength
  6. Low free lime


And the clinker minerals can be calculated using the following BOGUE equations:(4)


4- Alite;(Tri-Calcium silicate)

Responsible for initial strength

5- Belite;(Di-calcium silicate)

Responsible for final Strength

6- Celite;(Tri-Calcium Aluminate):

Responsible for setting time

7- Felite;(tetra-calcium aluminoferrite):

Responsible for setting properties & Color

8- Percent Liquid @ 1450°C (Liquid Phase) [25 – 27.5%](5)

 (*MgO should not exceed 2%)




If AR > 1.38

If AR < 1.38

If %LP= 30%, Dens and firm coating

%LP= 25%, Good coating conditions

%LP= 20%, Loose and porous coating


Al2O3,K2O & Na2O increasing the viscosity of liquid phase where Fe2O3 & SO3 decrease it;SO3, is not included in the equations for calculation of the amount of liquid phase present at different temperatures in a cement kiln! Alkali sulphates certainly melt contributing the flux and affecting its properties.(6) 



9- Potential Free Lime:

The presence of SrO and BaO in the raw material increases F.CaO

As SrO & BaO react with silica earlier than CaO!


10- Coating Tendency/index [27 – 32] 

If AW< 28 indicate light coating

If AW> 30 indicate heavy unstable coating, rings & snowmen (7)





11- Burnability Index:  [2.8 – 3.5]

12- Burnability Factor [100 – 110]

Parameters influencing burnability

  1. Residue on 212 µ sieve
  2. Residue on 90 µ sieve
  3. Size distribution of F.SiO2
  4. Degree of homogeneity (chemical & physical)
  5. Liquid phase of clinker temperature
  6. Moisture content of raw meals




13- Minimum burning zone temperature: 

14- Alkali Sulfate Ratio (A.S.R.):

This ratio indicate whether there is enough alkali to completely combine sulfur 

Optimum A.S.R. value = 1.0 and range from 0.6 to 1.4, this apply to raw material

Where Sulphate Modulus apply to hot meal

Optimum M.SO3 value = 0.9 and range from 0.8 to 1.0


15- Kiln feed uniformity factor index [KFUI](8)


Target <10


In general the steps to design the mix are:

  1. Analysis of raw materials
  2. Set LSF, SM & AM targets
  3. calculate the feeding proportion percentage required form each material to achieve these targets
  4. Calculate the expected clinker phases BOUGE Equation
  5. Calculate the other modules to predict the behavior of the raw mix in the kiln


Mainly the raw mix consist of three or four raw materials named respectively

  1. Three component system; limestone, Clay & Iron Ore
  2. Four component system; Limestone, Clay, Iron Ore & Bauxite

Calculate the Raw-Mix online; using the following table:-

Get raw-mix calculator for "Four Components System"

(4.99 $)


About the Calculator
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Recommend this page on:


[(2)Cement-Data-Book – Duda – 2nd edition]

[(3)Cement-Data-Book – Duda – 2nd edition]

[(4)Handbook of Designing Cement Plants, S P Deolalkar]

[(5)Cement plant operations hand book for dry process plants – Philip alsop & otheres special edition may 2003]


[(7)cement plant operations hand book for dry process plants – Philip alsop & otheres special edition may 2003]


Write a comment


  • mohamaad (Tuesday, September 15 15 02:58 am EDT)

    I want to ask how much liquid phase must be in white clinker and how must be the modulus LSF,AM,SM in rawmix
    thank you

  • Safwan Elfar (Tuesday, September 15 15 04:27 am EDT)

    Due to less Fe2O3 in the raw meal (<0.25%) SM=4+ , AM = 10+ , LSF = 0.95 & Liquid phase is a round 15%

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  • differences between google plus and facebook (Wednesday, November 04 15 05:36 am EST)

    Thanks for sharing your thoughts about Portland cement.

  • Muhammad Baiz (Sunday, November 15 15 01:21 pm EST)

    How to evalaute the quality of raw materials such as limestone and clay then determining the additives to meet the chemical composition of the raw mix to the standards. Best Regards

  • safwan Elfar (Sunday, November 15 15 02:19 pm EST)

    Thanks Baiz,
    The raw materials should contain the required oxides to maintain the previous modules specially LSF,SM & AM in addition to other oxides; MgO, K2O, Na2O, SO3 & chloride

  • Irfan (Wednesday, December 02 15 01:47 am EST)

    I have calculation of raw mix for 4 materials with using excel such as your mind. With using excel function we get easly proportion of each material

  • ALI (Monday, February 08 16 02:25 am EST)

    Thanks Mr. Safwan
    I got your blog quite helpful. May I know the some references of this article, I want to use them in my literature review?

  • safwan Elfar (Wednesday, February 10 16 12:00 am EST)

    Dear Mr. Ali,
    Thank you very much for your comment.
    kindly find more references via this link:


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