Late setting

Dear sirs,

We are using phospo zypsum (by product of fertilizer industry) for last 25 years for cement production. By using this gypsum we were never found late setting problem in cement as well as clinker ground in laboratory ball mill. Since 4 months it is observed that there is delaying initial & final setting times and also from the market. To control setting time the SO3 content in cement reduced from 2 to 1.4 % even then setting times were delayed.

There is no change in the chemical analysis of the clinker earlier as well as now (last 4 months). Earlier gypsum supplies were from settling pond where as now the fresh gypsum is compressed (for de-watering) and sent. Does this makes any difference which can influences the setting time.

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Re: Late setting

Possible reasons may be as given under,

1.Inadequate dehydration of gypsum.

2.Low C3A content.

3.Low reactivity of C3A.

I suspect also that your raw mix is low alkali content.Alakli rich raw mix additive can also reduce setting time.

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Re: Late setting

Dear Raj Sahu,

I am very much thank full to you for quick response, I request you to kindly  give some more details about low reactivity of C3A.

By maintaining high temperature in the cement mill is it possible to maintain adequate de hydration of gypsum.

Regards,

BLM

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Re: Late setting

With alkali rich raw mix, clinker C3A phase is more reactive and consequently its hydration reaction relatively fast.Mineralogical analysis of your clinker by XRD will tell which form of C3A present in your clinker.

With adequate cement mill outlet material temperature(115-120 deg. cent.) and adequate mill ventilation velocity (1.2-1.5 m/s for closed circuit mill) you may some extent improve gypsum dehydration.Cement SO3 further reduction and optimization may also help to get desired setting time.

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