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Technical Cement Forum / Low early strength of clinker

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BLM 04/07/2009 14:13:39

Low early strength of clinker

Dear Michael Clark

Recently we have changed the fixed grate angle from 18 to 14 deg to get the better secondary air as well as better cooling of clinker. The cooler is FONS (France). After changing the angle anticipated rise in secondary air is not obtained also new problem of red river started from both the sides of cooler.

Clinker produced in such condition when ground with gypsum in pilot ball mill is giving one day strength as in earlier case. Earlier we use to get 25 Mpa, where as now it varying between 5 to 20 MPa. Both 5 & 20 MPa when tested for 3 days are giving almost equal strength i.e.37 to 39 MPa. 7 days strengths are also in good limits.

What could be the reason for drop in one day strength as low as 5 MPa ?

When fly ash based cement produced with the low strength clinker the ement is showing good one day strength i.e.14 MPa. Where as OPC 53 grade cement is also showing similor strengths like PPC

Clinker samples were collected from red river zone as well as normally cooled area and tested for compressive strength. Strength of the both the samples are equal.

We request your kind advise.

Michael Clark 06/07/2009 08:22:06

It is very difficult to diagnose the cause of your problem. The loss of early strength development indicates some loss of reactivity of the clinker.
Perhaps caused by the clinker not being rapidly cooled. That is consistent with the formation of red rivers in the cooler. However, I have encountered many red rivers, without the loss of early strength you describe.

Davo 26/07/2009 18:20:38

Dear BLM

As you've written your cooler efficiency doesn't get better after modification, but worsen as I understand. After changing the angle of your grate, you've added the thickness of clinker and that can worsen the air to fuel balance, as well as the clinker quality. Regarding to early stage strength of cement, I think because of inefficient cooling process clinker phase and crystal's size changes takes place. The larger crystal size of clinker the less the early stage stength of cement etc.

If it's possible try to grind the clinker with smaller quantity of gypsum, maybe it can give you more or less good results.

Regards. Davit Babayan.

Ariel Diaz 11/05/2010 22:32:37

Dear Davit,

Recently we have detected a similar situation in our clinker but without doing any modification in the system.

We found an abnormal growth of the strength.

These are the normal parameters of our clinker average:
2 days strength: 25 MPa
7 days strength: 46 MPa
28 days strength: 56 MPa

The abnormal clinker produced the following parameters:
2 days strength: 19 MPa
7 days strength: 40 MPa
28 days strength: 59 MPa

We were checking the Bogue composition and found no significant changes in the content of C3S and C2S.
We are investigating the possibility that a change in the position of the burner is altering the crystallography of the clinker.
What we should observe in the microscopy analysis?
Do you have another suggestion for us to consider in the analysis?

Thank you. Ariel

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