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Technical Cement Forum / Issues with a product made with White Cement

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CementUser 12/09/2010 18:41:04

Issues with a product made with White Cement

Hi,

In the recent past we have been facing issues with a product made with white cement, hydrated lime, anhydrous calcium chloride, other calcium based minerals, pigments, water repellant additives, and surface active additives.

The product is made in Ball mills, with the raw materials being grinded and mixed for upto 3-4 hours and is fine powder. The finished product is discharged into bags and allowed to cool and settle before bags are sealed. The bags have plastic liners and the bags themselves are polypropylene bags.

The issue is, the product which initially has a powdery starts to have sand like feel sandy within a few days and later lumps are formed and the entire bag tends to solidify over a period of time which may be as short as 1-2 months.

The formulation of the product is unchanged and neither has the process or storage changed.

We have checked all our raw materials and have found the moisture content within 0.5%. Only white cement shows signs of some lumps. These lumps it seems tend to reappear even after grinding.

Is this due to faulty white cement? Or some other thing? How to prove that the white cement is the culprit or not?

We have also found that the according to the test reports of the white cement company, though all things are in range, they are fluctuating a lot (more than 10%) like setting time, particle size, strength etc.

Ted Krapkat 13/09/2010 03:49:23

One possible explanation could be an increase in the temperature of your product before bagging.

This could result in the continued dehydration of the gypsum in the cement within the sealed bag, causing lumps. The presence of calcium chloride would tend to exacerbate this problem because calcium chloride is a deliquescent dessicant. That is, it takes up water vapour and quickly dissolves into a liquid.

The high C3A content of white cement also means that it is more sensitive to moisture than regular cement, due to the formation of the mineral ettringite (3CaO.Al2O3.3CaSO4.32H2O). Ettringite forms needle-like crystals which can promote lumping of cement.

Do you measure the temperature of your product as it leaves the ball mill, or just before bagging? If so, has there been an increase in exit temperature?

Regards,

Ted.

CementUser 19/09/2010 06:14:39

Thank you for your reply.

The temperature of the mill has been constant and we have not changed any parameter in the working of the mill since the last 8 years. Yes, the temperature of the product in the mill does increase. That is why as a practice, we keep the finished product bag open for 30-45 min to let out the hot air and to cool the product before the bag is finally sealed.

Also this issue is not found in products with same characteristics, but no hydrated lime from the same mill.

Also we see a variation in sulphur content of the white cement from the range of 2.6 to 3.5. We find the issue of lumping more in those white cements where the sulphur content is higher.

Davo 19/09/2010 20:42:39

I agree with Ted. The problem you described, maybe because of content of CaCl2, maybe you have to decrese the content of the salt. CaCl2 absorb the water from the environment (or water from condesation of vapour within th bag).

One more thing too, the smaller particles tend to agregate and the combinations of risons, that described Ted, are the main rison of the problem.

Can I know where will be used such a binding material, you described

Davit Babayan

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