Concrete and Ballast Calculator

The proportions of materials for a C20P (P = Portland cement) mix are 1 x cement, 2 x fine aggregate (sand) and 4 x coarse aggregate. If you are using a premixed ballast, then 6 of these are mixed with 1 cement. If the sand and aggregates are dry, then a water to cement ratio of approximately 0.55 should be used, For example, if you require 25kg of cement in your mix, then 25 x 0.55 = 13.75kg (liters) of water. This is the maximum amount of water that should be used. Most of the time however, the sand etc is damp, or even very wet, and care has to be taken to ensure your mix does not become too sloppy. It should be able to support itself, almost fully, in a heap on the shovel.

When mixing a very strong mix, normally labeled C35P the mix is 1 cement, 1 stone and 2 sand or 1 cement to 3 ready mixed aggregate.

When mixing concrete you will find that, while the ballast will heap up nicely on your shovel, the cement will slide off. This will give you incorrect proportions when mixing,1 of cement should be equal to 1 of ballast. It is better to measure your quantities using a bucket to ensure correct proportions. Mixing by hand is a bad idea unless you only have a tiny amount to do. Only very rarely will you be able to get the cement evenly distributed throughout the mix and this leads to weak concrete so always use a cement mixer.

To ensure a well mixed batch we suggest you add your ingredients to the mixer in the following order. 75% of the water followed by 50% of the aggregates. Add all of the cement and then the rest of the aggregates and the remainder of the water.

Input your dimensions in meters I.E.  500mm = 0.50 meters then click the volume button the answer will be given in cubic meters. Then click on the quantities button to get the amounts of cement sand and aggregate.