I would like to know how to estimate the quantity of grinding media of each size required for a ball mill using the data mill size, number of chambers and type of material to be ground. Kindly explain me what formula is to be used.

The total quantity of media required for each chamber is determined by calculating the internal volume of the chambers. A rule of thumb is to change the first chamber to 30 per cent of this volume and the second chamber to 27 per cent. You can use 4.6t/m₃ as the density of grinding media. As for the individual ball size gradings this has to be determined by conducting a series of axial tests in the mill while you are building up the media charge.

What ratios can be suggested for ternary blending of cement with PFA and GGBS. Taking into account that the cement will be of Cem I quality and we would like to achieve a 32.5MPa product.

The ratios for blending GGBS or fly ash to achieve a 32.5MPa product will depend on the hydraulic activity of the individual components. The only way to define these ratios is going to be by the process of producing trial mixes and physical testing of concrete made from the mixes. It may be possible to add up to 65 per cent GGBS as this material is both cementitious and pozzolanic. The limit of PFA addition will be much lower, perhaps around 25 per cent, as this is only pozzolanic.