Estimating the quantity of dryblended concrete
When concrete is to be mixed on site rather than ordered from a readymixed concrete supplier, an estimate of the materials requirement is necessary. The concrete can be purchased in bags already proportioned as dryblended cement/sand/aggregate.
Concrete in dryblended bags for the DIY market will have printed advice on the bag stating the volume of concrete it will provide when water is added. Generally dryblended concrete is sold in 25kg bags. By dividing the estimated concrete volume needed for a project by the stated volume the required number of bags for the project can be determined
Example:
The estimated concrete volume for driveway slab = 1.65 m^{3} Using 25 kg bags of dryblended concrete (each producing say 0.010 m^{3} of concrete) Number of bags needed = 1.65 / 0.010 = 160.6 = 165
