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)?

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.

We are 3100tpd cement plant situated in the Arabian Gulf. We have four cement silos 10,000t each at our plant, we are facing the problem of lump formation in silos, which is causing cement extraction delays and is also effecting our market reputation as well. Our cement mill is 136tph rated capacity (OPC) closed-circuit with water spray system (made in-house). The humidity reaches 80 to 90 per cent in summer, as it is a coastal area. Till now we have not come to any conclusion about the cause of lump formation in our plant. Can you please suggest us if grinding aid may help in solving the above said problem, how technically, and of course to what extent.

Given your location and the humidity you suffer in the summer, the question you must answer is whether the lump formation is caused by the ambient humidity in the air in the free space in the silo or continued dehydration of gypsum in the silo. I suspect the problem will be continued dehydration of gypsum in the silo. To solve this you must carefully control the temperature of the cement entering the silo. The installation of a cement cooler may be necessary in your climate to bring the cement temperature below 80 degrees Centigrade.