Voids Method:

The principle involved in this method is that the voids in the coarse aggregate are to be filled in by the fine aggregates and the voids in the fine aggregate are to be filled in by cement paste. As like, it is necessary to determine voids in fine and coarse aggregates.

Volume of excellent aggregate need for 1cu-m of coarse aggregate = Total voids in coarse aggregate + 10% aggregate extra to allow for additional voids created by wedging action.

Volume of cement paste need for 1cu-m of coarse aggregate = Total volume of voids in fine aggregate + 15% used with 1cu-m of coarse aggregate extra to allow for additional voids created by wedging action.

The volume of dry cement is usually calculated as equal to 1.2 × Volume of cement paste.

For determining the percentage of voids, aggregate are filled up to the top within a vessel of known volume. Within this vessel, measured volume of water is poured in order to fill it.

Percentage of voids = Measured volume of water added into the vessel/ Total volume of aggregate filled in the vessel × 100