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.

We will appreciate your support clarifying the following points:
1-False air effect upon the (increase/decrease) of dust load in a closed system of air swept type ball mill (between the mill outlet duct-seperator-cyclones-filter-stack). 2 - Also, will the dust resistivity increase/decrease?

In an air-swept mill false air is usually introduced at the bottom of the ascension pipe in order to ensure there is sufficient volume, density and velocity of air to lift the ground material up the ascension pipe and through the separator. The amount of dust being carried up the ascension pipe is the same, however the volume of air is greater therefore the overall effect is a dilution of the dust load. In principle the false air will cause a reduction of the temperature and this will reduce the resistivity of the dust improving the electrostatic precipitation.