LIMITS OF C3A,C2S,C4AF

KEEPING C3S CONSTANT WHAT IS THE OPTIMUM LEVEL OF C3A,C4AF FOR RAW MIX DESIGN?

WHICH SHOULD BE GREATER C3A OR C4AF & WHY?

WHAT IS THE IMPACT OF LOW C2S ?

ALSO WHAT IS THE OPTIMUM CONTENT OF C3A & C2S IN CASE OF WHITE CEMENT & WHY?

ENGR.

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re LIMITS OF C3A,C2S,C4AF

Hello xxxx,

These are difficult questions to answer because they are rather non-specific.

The optimum clinker mineralogy for any given cement manufacturing plant depends on many things including;-

• Type of cement(s) being produced.
• Market requirements (cement performance).
• Customer expectations.
• Cost and availability of raw materials and corrective materials.

However the clinker manufacturing process itself imposes limits on the levels of clinker minerals.

For grey cement;-

• The clinker LSF needs to be less than 100 (preferably 94 - 98%) to prevent excessive amounts of free lime. The LSF controls the ratio of C3S to C2S in the clinker and this relationship therefore imposes limits on the C3S (50 - 65%) and C2S (5 - 20% ) content of the clinker.
• To promote good coating formation in the kiln burning zone, the liquid phase should be between about 23 - 28%. This automatically limits the total silicates (C3S +C2S) to ~70 - 75% and the S.R. to between 2 .0 and 3.0.
• For proper clinker nodulisation and stable kiln operation the A.R. needs to be between 1.3 and 2.5 to control the liquid phase viscosity. Since the A.R. controls the amount of C3A in the clinker, this means that C3A is limited to roughly 5 -15%.

So you can see that the initial limit ranges for the clinker minerals are set by the kiln process and then these rather broad limits are refined to much narrower ranges according to the type of cement produced, and the performance requirements of that cement in the marketplace.

Regards,

Ted.

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re LIMITS OF C3A,C2S,C4AF

Sir ,

Is there any relation ship / Connection between the toatl cabonet (TC) and LSF. How can i predict if i have one indicator ( TC or LSF) . How much the content of TC to produce good quality of Clinker its C3S over 55 ? And how much the LSF accordingly , Can you please advise

ILA

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re LIMITS OF C3A,C2S,C4AF

Hello ILA,

I presume you are referring to raw meal?  If so, then for raw meal made with pure limestone as the only source of calcium there is a direct correlation between the total carbonate content of raw meal and its LSF because, in this case, the CaO used in the LSF calculation comes exclusively from the calcium carbonate in the limestone.

However, if significant amounts of magnesium carbonate are present in the limestone (eg. dolomitic limestone) then the correlation between total carbonate content and LSF of the raw meal breaks down. This is because that although all of the magnesium carbonate is reported in the total carbonate analysis, normally only about 2% MgO can be incorporated into the clinker minerals, the rest is deposited as free MgO (periclase).

Do you have a high MgO content (>1.5%) in your raw meal and how variable is it?

The C3S content of the final clinker is influenced not only by the raw meal LSF, but also by the quantity and chemistry of the ash from the fuel(s), as well as the quantity and chemistry of any additional AFR material streams (eg spent cell liner) which have a significant SiO2, Al2O3, Fe2O3 or CaO content. This means that, the only case where the LSF of the raw meal directly correlates with the C3S content of the clinker is when you use natural gas (or oil) as the only fuel, and your raw meal is the only other input to the kiln and clinker is the only output. These days very few cement plants are this simple.

Only if you know the quantities and chemical analyses of all your kiln inputs and outputs (including alkali bypass dust etc) can you hope to calculate the final clinker chemistry and hence the potential clinker mineralogy.

I hope this answers your questions.

Regards,

Ted.

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