1156 posts
Quality control Question 39
How can the bulk density of cement change? Kindly describe the factors responsible? What are the consequences of bulk density of cement on concrete? How to increase the bulk density of cement? Do you suggest to increase iron ore content in raw meal to increase cement density? What is the range of bulk density and specific gravity for ordinary Portland cement (BS 1997)?
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1156 posts
Re: Quality control
The bulk density of a particular cement can vary due to compaction or due to chemical reactions with the atmosphere or any water the cement comes into contact with. If you specifically want to change the bulk density of freshly ground cement then you would need to adjust the chemical and mineralogical composition. Increased iron oxide would do this but the effects would be very slight. I would also expect problems with excessive coating and ring formation in the kiln. There are certain concrete applications where high density concrete is specified (eg radiation shielding). This is achieved by using heavyweight aggregates such as barium carbonate or sulphate rather than by increasing the bulk density of the cement itself. The bulk density of cement is around 1.5 tonnes per cubic metre.
1156 posts
Quality control Question 40
Our clinker chemical composition is as follows: SiO2= 21 per cent; CaO= 64 per cent; Al2O3 = 6.0 per cent; Fe2O3= 5.2 ; K2O = 0.4 per cent; SO3 = 0.55 per cent; MgO =1.0 per cent; Free CaO = 1.0 per cent and the liquid = 34.5 per cent. Liter Wt 1380g/ l. If there is slight reduction in the liquid the clinker becomes dusty though the free CaO is under control. Here it seems the Al2O3 comes from limestone does not get into liquid though the calculated liquid is high.If slight reduction in Fe2O3 content results in dusty clinker. We add aluminous laterite and hematite ore as fluxes. The question is how to differentiate between the actual liquid and calculated liquid.Does the optical microscopy help in this regard? From your experience give a clear picture on how to reduce the liquid content with improved nodulisation and to have better refractory life in the burning zone. Even the Spinel bricks give only( refra mag-85 of refratecnik) six month's life.
1156 posts
Re: Quality control
You are correct the theoretical liquid content of your clinker is very high. The litre weight is also high indicating a very dense (almost fused) clinker. Some Al2O3 will undoubtedly be taken into solid solution in the alite phase. Optical microscopy can indeed tell you the true liquid content (and the true alite, belite and free CaO content). There are photographic and computer pattern recognition systems available that will do this for you and eliminate the variation between microscopists. With regard to refractory life the liquid content and its properties are important. The viscosity of the flux is a critical consideration. Too fluid a flux can lead to dusting. These inter-relationships are very complex. To answer your questions properly would require a full and detailed process investigation involving microscopic analysis of frequent samples coupled with detailed process data over an extended period.