108 posts
Free Lime
Dears,
How to calculate/analyse a moistened clinker for its free lime (CaO), since after
absorbing moisture C3S and C2S will release Ca(OH)2 which will react with
HCl on titration and thus increase its value.(Ethylene Glycol Method).
Regards,
Gulam Dastgir
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324 posts
Re: Free Lime
Absolutely right. This is why the free lime content of a quenched, white clinker cannot be reliably measured by the ethylene glycol titration method. The loss in weight involved in driving off the combined H2O in the Ca(OH)2 should be determined to arrive at a correction factor.
108 posts
537 posts
Re: Free Lime
Hello Gulam,
It really depends on how long the clinker has been exposed to moisture and whether or not it has also been significantly exposed to the atmosphere. (pretty much unavoidable really)
Freshly moistened clinker will only contain free lime as CaO and Ca(OH)2. However, fairly quickly you will also get carbonation of the Ca(OH)2 into CaCO3 by exposure to atmospheric CO2.
This complicates the matter of calculating the free lime by determining the loss in weight of the combined water because the CaCO3 that has formed will also lose CO2 when heated. Even if you heat the sample to only 580 deg C. ( the decomposition point of Ca(OH)2), substantial CO2 will also be lost from any CaCO3 present during the analysis.
Any free lime result calculated in this way will, at best, be a very rough estimate.
The only way to accurately analyse the Free CaO content of clinker exposed to moisture and atmospheric CO2 is by XRD.
These days many cement plants use XRD for routine clinker free lime analysis.
Best Regards,
Ted.