Always allow for the consolidation of all-in ballast (a mixture of sand and aggregate) when estimating the amount required for concreting. When mixed in water. All-in ballast is reduced to seven-tenths of its original volume.
The following table gives the proportions for various thicknesses of concrete spread over an area of lOsqm 12sqyd. The mix required for a smaller or larger area can easily be calculated from it.
Depending on the strength of the mix required, the amount of cement needed is usually three to four bags per cubic metre or cubic yard. Used to bind the sand and aggregate, cement is absorbed within the ballast and therefore does not affect estimates of volume.