If air cooled slag is used as a raw material for kiln , replacing uncalcined calcium carbonate, will the calcium silicates, aluminates, etc. revert back to free state, so they can reform clinker crystals of cement design proportions? Will the existing sicates go to C₂S state with the increased temperature and time. In other words could this slag combined with correction proportions of silica, iron, alumina, calcium be used as a primary raw material for a kiln feed? If there is a reversion of the state of the compound will there be a requirement for additional heat (as opposed to the exothermic heat released to compound formation) ? Would there be any big color changes if air cooled slag was used as a primary raw material.

There could be a number of causes of the high free CaO content of your clinker despite the fact that the lime saturation of the clinker is only 92 per cent. The fineness of the kiln feed is one factr and also the contents of MgO and K₂O. If you can tell me those I will be in a better position to diagnose the problem.

We are getting very high free lime in clinker. Some times it goes up to 5 per cent. Normally it remains 2 to 2.5 per cent. We are firing 100 per cent South African and Chinese origin coal. Our kiln feed analysis is 95 -96 per cent LSF, 2.35 Silica Modulus, and 1.85 - 1.900 Alumina modulus. In clinker we get 92 per cent, LSF, 2.10 SM and 2.1 AM. We are using Duoflex burner of FLS. What is your opinion about the causes of free lime.

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.