Concrete Mixes by Weight and Volume

A Table for Concrete Mixes by Weight in Kilograms,

by Bag, and by Cubic Meter, for Various Strengths

We have had numerous requests for concrete mix ratios by weight, by volume, and by mass. Here is a table that was released by the Cement and Concrete Institute for trial concrete mixes from 10MPa to 40MPa. These are trial mixes and should be used to test your concrete before it is used in any construction work. Your “competent person” or project manager should always assess and approve any concrete work undertaken on your site.

The mix proportions in the table are by mass and volume, using different size stones, for different strengths of concrete. You must add water to the mixture until it becomes workable; you can judge this by eye. The difference between various types of cement and aggregates is not taken into account with these mixes. Make sure that the water is kept together with the mix and is not allowed to drain/run away as this could result in a weaker mix.

NOTE:

These proportions are based on the assumption that a CEM-type cement of strength class 32,5 will be used. The cement of strength class 42,5 or higher will give a stronger concrete but may be less economical. Cement with high extender contents (eg CEM 11/B or CEM 11) will develop strength more slowly and will require particular care with curing. Masonry cement complying with SABS ENV 413-1 should only be used with specialist advice.

The amount of water required is not given in the table. The mix should contain enough water to achieve the required consistency. Consistency may be assessed by eye or measured by carrying out a slump test (SABS Method 862-1: 1994)

A mix made according to this table, and to the required consistency, should be assessed for workability and stone content before being used on a large scale.

Quantities of materials per cubic meter of concrete are net. Allow for wastage when ordering – for instance 3% on cement and 10% on aggregates.

A standard bag of cement weighs 50kg so the equivalent quantities and weights are:

1 Bag cement = 50kg = 0.033m³ to 0.035m³ (cubic metre)

Below is the nominal mix proportions (also referred to as the ratios of mixes) for different strength categories, using a 19mm stone.

NB. Low would be average 15MPa, medium 25MPa and high 35MPa. This is a guide only and quantities must be adjusted for the final requirements and specified by a “competent person“.