1156 posts
Cement blending Question 3
What would be the recommended ball charge and combination to produce masonry cement at 6000 cm2/g. the component percentage are clinker= 50 per cent, limestone=45 per cent, gypsum=5 per cent. I tried researching on this, but the suggested ball charge and combination would always refer to OPC at 3000-3200cm2/g. We are still in the process of rehabilitating an old cement mill, and except for the ball charge, the mill internals are in good condition. What frequency of axial tests would you recommend? We intend to start the tests at 85 per cent ball charge.
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1156 posts
Re: Cement blending
I am not surprised that you could not find what you were looking for by research. You will have to find the optimum ball charge for your particular mill making this masonry cement by a series of axial tests while charging the mill to 100 per cent media loading. The only thing you can predict is that you will need a much smaller overall ball charge due to the high fineness you require and the easy grindability of the limestone. I would start the axial tests at a lower filling degree. Probably 60 per cent. If you leave it to 85 per cent you might not be able to correct the total charge to the optimum with the remaining 15 per cent.
1156 posts
1156 posts
Re: Cement blending
The simple answer is "around one per cent", but the exact response may rather depend what you mean by "lime" and what class of cement you are talking about! Portland cement is ground from a clinker produced by heat treatment of a raw mix that consists mainly of finely-ground limestone and shale. On heating, the limestone forms lime which, in due course, conbines with other substances to form calcium silicates and aluminates and there is only one per cent or so residual uncombined lime remaining. Cement sets and gains strength through the reaction of these substances with water. So, some people would say that a lot of lime goes into cement: if you analyse the clinker and do not take account of the fact that the lime is combined as aluminates and silicates, then about 65 per cent of ordinary Portland cement is "lime". Now when it comes to making mortar, we have a different story. A long time ago, lime/sand mortars were used (about 25% lime in the mix); then, to get more rapid strength development and higher final strength, people started to add cement. (Just using cement and sand leaves you with a lot af sand and not much cement and a harsh mix that is difficult to work with a trowel - and if you add more cement to overcome this then the mortar becomes too strong for general use.) So, some traditional mortar mixes are 2 parts of cement plus 1 of lime and 9 of sand ( or 2 - 2 - 12, or 2 - 6- 24 are also OK). You can buy masonry cements instead: in North America these are typically made from about 50% Portland cement interground with an inert material such as limestone and a plasticiser to aid workability and you can mix 1 part with 3 parts of sand to get a mortar roughly equivalent to one of the traditional mixes. Now, if someone says "lime" instead of "limestone" - as is common in some regions of the world - you need to change our first answer quite a bit! Concrete mix design is quite another field. Concrete is basically a mixture of aggregate - crushed stones or gravel - in which the voids have been filled by a mortar mix (sand and cement) that yields suitable flow properties when fresh and, in due course, appropriate strength. (Add too much water to get it to flow OK and you lose out on ultimate strength; add too little water and the mix will not flow into all the corners where it is needed!) Most builders' merchants, do-it-yourself outlets and suppliers of cement will give you rules of thumb as to what mixes to use for different jobs.