11 posts
Re: Cement Shelf life
Dear Ted, Ghulam
Thank you for your technical support related to the subject.
I need one more help.
1. Is there any problem to add limestone with cement intergrinding ( up to 5 % in OPC)?
2. What is the factor can influence the cement production up to 10 %.
3. Is there any formula to calculate the grindablity test by the lab ball mill?
With regards,
Sundar
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537 posts
Re: Cement Shelf life
Hello Sundar,
Cement testing:
1. Is there any problem to add limestone with cement intergrinding ( up to 5 % in OPC)?
No, intergrinding limestone with clinker and gypsum to produce PLC (Portland Limestone Cement) is common in many parts of the world.
5% limestone is fairly typical, however some standards allow much more. (up to 20 or 30%) From a grinding point of view, 30% is pretty much the limit because studies have shown that limestone contents above 30% obstruct the grinding of both clinker and limestone.
In addition, the more limestone you add the less clinker minerals are available for hydration. Therefore, at high limestone addition rates, care must be taken to ensure that the strength and workability of your concrete is maintained withinin acceptable limits. Limestone quality should be kept as high as possible, as significant clay content can adversely effect concrete properties
So, depending on the quality of the limestone and the reactivity of your clinker, 5% limestone addition should not affect the final concrete properties too much.
Limestone not only acts as an inert filler (which makes the concrete more dense by filling small pores in the concrete which would normally be filled by water), it also reacts chemically with the clinker minerals, particularly C3A with which it forms carboaluminate phases. See this paper for more information;-
http://www.allbusiness.com/manufacturing/nonmetallic-mineral-product-mfg-cement/13705935-1.html
Limestone content can be controlled by measuring the Loss On Ignition of the cement. (I can supply more information on this procedure if you need it.)
2. What is the factor can influence the cement production up to 10 %.
There is evidence to suggest that only small changes to cement properties are required in order to increase from 5% limestone to 10% limestone addition. All of the points mentioned above apply even more so to 10% limestone addition.
The introduction of limestone addition, or any changes in limestone content should always be verified by plant trials, including extensive testing of mortar and concrete properties.
3. Is there any formula to calculate the grindablity test by the lab ball mill?
The grindability index is often calculated from the number of mill revolutions required to achieve a predetermined cement fineness.(either Blaine or sieve residues)
This can be determined by taking representative samples from the lab ball mill after successive incremental numbers of revolutions, and testing these samples for fineness. The number of samples should be sufficient to cover a range that includes two or three values both below and above the target fineness.
These values can be plotted on a graph in Excel and the exact number of revolutions required to achieve the desired target Blaine can be determined. The number of revolutions is then divided by a scaling factor to obtain a grindability index. This factor depends largely on the size of your lab mill, the ball charge mass, ball size distribution, and the load mass.
Note that a grindability index determined in this way can only be used for comparing samples ground in the same lab mill, under identical conditions. If you need a standard grindability index you will have to use the Bond Work index method, which is available in many places in the scientific literature and on the internet.
Regards,
Ted.
17 posts
11 posts
Re: Cement Shelf life
Dear Ted Thank you.
How to avoid the pack setting ?
With regards,
Sundar