The compressive strength of concrete in the UK is measured with a cube test which provides the manufacturer and customer with the strength of the concrete at both 7 and 28 days. Concrete cubes are crushed in a testing laboratory where the compressive strength can be accurately measured.
The compressive strength of concrete depends on many factors such as the water-cement ratio, cement strength, quality of aggregates used and quality control during the production of concrete.
When concrete cubes are made, in order to check the quality of the concrete, there are a set of rules which need to be followed to ensure that the results are accurate. All concrete cubes should be made in accordance with BS EN 12390-2, ‘Testing hardened concrete. Making and curing specimens for strength tests’.
Cubes should be cast, in sets of 2 or 3, as soon as the concrete has been sampled and made as near to their final storage position as is practical.
The cube mould should be clean and lightly oiled. The mould should then be filled in 50mm layers and compacted with a steel tamping bar (a minimum of 25 or 35 tamps per layer for a 100 or 150mm mould respectively).
After tamping each layer, the mould should be lifted slightly and dropped or the sides tapped to close the top surface of each layer. The final layer should slightly overfill the mould. Finally, the top layer should be trowelled off and made level with the top of the mould.
All sampling and test equipment should be cleaned immediately after use.
The fresh cube should be kept away from extremes of heat and cold. Ideally, they should be covered to prevent surface evaporation and stored as close to 20°C as possible, ideally in a temperature controlled environment. After 24 hours the moulds are stripped and the cubes placed into the curing tank, which will be maintained at the required temperature.
The cubes are then sent for testing, with the first cube being crushed at 7 days, and the second being crushed at 28 days. This is done to establish the compressive strength of the hardened concrete and is measured in N/mm2 or MPa. For example, an RC28/35 concrete would be expected to reach a minimum strength of 35N/mm2. The “28” in RC28/35 refers to the strength requirement in the rest of Europe, as they do cylindrical tests, rather than cubes.
We deliver to the following towns and their surrounding areas: Bedale, Boroughbridge, Catterick, Easingwold, Harrogate, Knaresborough, Leeming, Leyburn, Masham, Northallerton, Ripon, Thirsk and Wetherby.
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