Oct 2017 A SOLID GUIDELINE TO CONCRETE MIXING
Concrete is made up of four elements: cement, sand, stone (aggregate) and water. The cement: sand: stone ratio is critical as it determines the compressive strength of the concrete, which in turn establishes the capacity of the structure you build to withstand loads. We offer a guideline to solid concrete mixing proportions for optimal compressive strength.
Choose the right cement for the right application
Point of departure would be to select the right cement for the right application and to check that it complies with the relevant specifications to ensure a lasting end product. Click here for more information on the types of cement and its applications.
Input equals output
Apart from choosing the right type of cement for the right application, it is also critical to take an uncompromising approach to the quality of the cement you choose, to ensure structures that will last. The range of cement supplied by Sephaku Cement does not only meet, but also exceeds the relevant standards of the built environment in South Africa:
- Manufactured according to the requirements of the National Regulator for Compulsory Standards;
- Sold under a Letter of Authority (LOA);
- Carry the SABS mark certification ; and
- In accordance with the South African National Standards (SANS) 50197-1.
Consult manufacturers’ guidelines for ideal mixing proportions
As soon as you’ve selected the cement that is most suited to your application, you will need to consult the manufacturers’ guidelines to determine the ideal concrete mixing proportions. The mixing proportions are also subject to the strength of concrete you need, which can generally be classified in the following five groups:
- High strength (25 – 30 MPa)
- Medium strength (20 – 25 MPa)
- Low strength (10 – 15 MPa)
- Mortar (5 MPa)
- Dry, lean mixes (7 – 14 MPa)
Examples of concrete mixing ratios
For the purposes of this illustration, we will take a look at the Sephaku 32, a 32,5N general purpose blended cement that reaches compressive strength at a normal rate and that is suitable for an extensive range of building applications, including general domestic or building concrete, mortar, plaster and screed.
The guidelines allow for minimal wastage of between 5-10% and are based on a 65-litre builder’s wheelbarrow. Please note that one 65-litre wheelbarrow load of cement is equal to two 50kg bags in volume.
- Dry, lean mixes for brick and block manufacturing: One wheelbarrow of cement (= 2 x 50kg pockets) and eight wheelbarrows of sand.
- General purpose mortar for bricklaying and plastering: One wheelbarrow of cement and six wheelbarrows of sand.
- Low strength concrete for foundations, domestic flooring, steps, paths and fencing: One wheelbarrow of cement, four wheelbarrows of sand and four wheelbarrows of stone.
- Medium strength concrete for paths, driveways and light-duty floors: One wheelbarrow of cement, three wheelbarrows of sand and three wheelbarrows of stone.
- High strength concrete for columns, slabs and heavy-duty industrial flooring: One wheelbarrow of cement, two wheelbarrows of sand and two wheelbarrows of stone.
These concrete mixing proportions will vary, subject to the type of cement that is required. For a detailed guideline on concrete mixing proportions of 42, 5 and 52, 5 types of cement, click here to download the Sephaku Cement product brochure now.