C3A by XRD

Dear Experts,

The chemical analysis of clinker by XRF is showning 5.0 % C3A, where as the same sample analysed by XRD shows C3A cub: 1.5 % & C3A orho: 2.10%. why is the difference so. Also our initial setting time of cement is very higy (350 mts). To control initial setting time Alumina content increased by 0.50 % in clinker, even then there is no chnage in initial setting time and C3A phase in the XRD.

Your suggesions are invited for increasing the C3A phase in XRD and also controlling the initial setting time or any other suggesions to control initial setting time are highly appreciated.

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Re: C3A by XRD

BLM:

The chemical analysis of clinker by XRF is showning 5.0 % C3A, where as the same sample analysed by XRD shows C3A cub: 1.5 % & C3A orho: 2.10%. why is the difference so.

 The Bogue mineral phase composition calculated using XRFchemical analyses is purely theoretical and assumes equilibrium conditions have been reached in the kiln. Rarely do these calculated mineral contents agree well with XRD analyses. For example C3S by XRF can be up to 20% lower than the actual XRD result. The difference in C3A between XRF (5.0%) and XRD (3.6%) that you quoted above is fairly normal.

BLM:

Also our initial setting time of cement is very higy (350 mts). To control initial setting time Alumina content increased by 0.50 % in clinker, even then there is no chnage in initial setting time and C3A phase in the XRD.

When you increased your clinker Al2O3 content, what happened to your Fe2O3? Did your alumina ratio increase or stay the same? Remember that Al2O3 can also form C4AF, depending on the ratio of alumina to iron.  C3A content is controlled by increasing or decreasing the Alumina Ratio, which is usually achieved by reducing the Fe2O3 content of the clinker. (white cement clinker is an extreme example)

Also, C3A is only one side of the setting time equation. Gypsum content probably has a more important influence than small changes in C3A. Have you performed any gypsum optimisation trials? This is normally a good idea if you intend to significantly change your C3A level in any case.

BLM:

Your suggesions are invited for increasing the C3A phase in XRD and also controlling the initial setting time or any other suggesions to control initial setting time are highly appreciated.

If you wish to Increase your C3A, I suggest you do so by reducing your clinker's iron content to increase your alumina ratio. However I strongly suggest that you also look at possibly reducing your SO3 content somewhat because this can have a strong effect on setting times.

Another thing that can influence setting times is clinker reactivity. Badly over-burned clinker (free lime <0.5%) can have reduced speed of hydration and therefore longer setting times. Aim for an optimum free lime of 1-2%.

You may also consider increasing your cement fineness.

Best Regards,

Ted.

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Re: C3A by XRD

Thank u Mr. Ted ,

Normally our free lime content is in between 1.5 to 2.00 % & SO3 in cement is 1.60 to 1.70%. If we reduce the SO3 content further compresseve strengths are comming down by around 20 kg /cm2. So Iam thinking that better to raise the C3A cntent from 6.00 % to 6.50/7.00% to reduce the initial setting time by increasing heat of hydration. please give your sugestion in this regard. We are using phospho gypsum in cement grinding.

Once again thank u for responding.

Regards,

BLM 

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Re: C3A by XRD

BLM:

Normally our free lime content is in between 1.5 to 2.00 %

Your clinker is certainly not over-burned at that free lime. It is already at optimum. 

BLM:

SO3 in cement is 1.60 to 1.70%. If we reduce the SO3 content further compresseve strengths are comming down by around 20 kg /cm2. So Iam thinking that better to raise the C3A cntent from 6.00 % to 6.50/7.00% to reduce the initial setting time by increasing heat of hydration. please give your sugestion in this regard. We are using phospho gypsum in cement grinding.

I guess that is the only option you have under those circumstances. However, I doubt that a change in C3A of only 0.5% will have a significant effect on setting times. I suggest you try increasing your C3A to 7% and see what happens.

Finer grinding is an easy but more expensive option, if all else fails.

Good luck,

Ted.

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