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Concrete Cube Tests Explained

pdf icon. download how to guide for concrete cube testing

Tell me about concrete cube tests…

The concrete cube test is a simple, inexpensive test of the compressive strength of concrete, providing you peace of mind that your concrete is fit for purpose and in line with BS EN 12390. Samples are taken from the concrete as it is cast into the structure, cured under standard conditions and crushed to determine the maximum compressive strength in our UKAS accredited Laboratory. If this test is not carried out, or not done properly, there can be costs and losses to your business due to delay, further investigation, possible litigation process or removal and replacement of faulty concrete. Click on the following link for more information on the BSI standard BS EN 12390.

Download our UKAS certificate here

This is the main compliance test and concrete testing service for all structural concrete, which tends to be specified in terms of required strength at 28 days. E.g. a C32/40 grade of concrete should achieve a minimum strength of 40N/mm² at 28 days. (The 32 figure refers to a cylinder tests common in some European countries but rarely used in the UK)

The concrete cube test remains almost unchanged from when we first opened our doors forty years ago and was well established even then. Many thousands of concrete cubes pass through our UKAS accredited laboratories every year. Visitors to our Testcrete Head Office at Carlton cannot fail to notice that we have about half a mile of access roads made form surplus concrete cubes!

What will the results tell me?

You will receive a Testcrete certificate stating the density of the concrete tested and the compressive strength of the concrete in N/mm², which can be compared with the specification.

There may be other items in the specification such as minimum cement content and maximum water: cement ratio. Although the concrete cube tests will not tell you directly whether these have been complied with, they are strength related and a low strength may indicate problems with water or cement content.

What constitutes a pass?

Strictly speaking, if the 28 days cube results are above the specified strength, then that is a pass result. However there are more factors involved over a period of several tests. If the results are only just above the minimum or are very variable, then, statistically, there may be a very high probability that there will be some failures over a period of time.

To allow for the inherent variability of concrete, the average results should be about 8-10 N/mm² above the specified strength to minimise the possibility of failures. Please be aware that many concrete cube failures are due to poor quality cubes.

Ok, so who makes these cubes?

You can make your own concrete cubes if you wish, but we are finding that more and more of our clients are having these concrete cubes made by our trained technicians. This lessens the likelihood of poor quality cubes being made and a concrete cube failing through no fault of the concrete itself. A trained technician can come to your site, to coincide with your planned concrete pour, and collect a sample of concrete to make into cubes. The concrete cubes will then be bought back to the laboratory for curing and testing.

What if I want to make my own concrete cubes?

No problem. You will need;

  • a quantity of purpose made, machined, steel moulds
  • sampling equipment
  • tools and mould oil for stripping and cleaning
  • a thermostatically controlled curing tank to store the cubes
  • a shed with a bench and a power supply
  • you will also need someone who is trained to use all the equipment listed and keep proper records.

We can supply all of the equipment on a purchase or hire basis and train your staff, just contact us for details. When is this most common?

A few dont’s for concrete cubes

Cube failures can be very expensive, in terms of both time and money, whilst they are resolved. Ensure that you avoid them if at all possible by following our tips;

Don’t make your own moulds - Over the years we have seen a wonderful selection of home-made concrete cube moulds, from those that a cabinet maker would be proud of, to those made from five old bits of chipboard nailed together. None were any good whatsoever. The moulds must be made from machined steel to ensure perfect contact with the testing machine.

Don’t be tempted by single use polystyrene moulds that you may have seen, to make concrete cubes. These are suitable for very low strength concrete such as trench fill. When used for structural concrete, you will be left with an orange peel surface that, again, will not make full contact with the testing machine.

Don’t give the job to your most junior, inexperienced member of the staff unless you are satisfied that they are conscientious and fully trained.

What if Testcrete make the concrete cubes?

We can’t guarantee that you will never have a cube failure, but we can promise you that it won’t be due to badly made cubes.

All you need to do is book our technician at the same time as you order the concrete and we will take it from there.

The procedure relieves you of all the problems of finding and maintaining equipment, looking after the cubes and ensuring that someone is available to make them. Your site staff probably have plenty to do during a concrete pour without worrying about cubes, after all you wouldn’t want the hassle of mixing your own concrete – why make your own cubes?

On the day:

1. Our trained technician will arrive at the appointed time with his own equipment.

2. He will sample the concrete in the prescribed manner

3. Make rge required sets of cubes

4. Complete all necessary paperwork.

All he needs from you is access for his van to the point of discharge next to the truck mixer.

What happens after the cubes are made?

If we make them, we will take them straight back to the laboratory. They will be stripped and placed in our curing tanks as soon as possible.

If you make them, strip them, mark them with a date and reference number and place them in your own tank, call Testcrete and we will collect them when we are next in your area.

When the due date arrives, we will test the cubes in accordance with our UKAS accredited procedures and issue a report.

How many cubes do we need?

Cubes should always be made in sets. The number of cubes in the set will vary according to your needs but we recommend a minimum of 4. One for 7 day test, 2 for 28 days test and a spare. Each set should be made from one batch of concrete. Although the 28th day strength is the main criterion, a 7 day test gives a good idea of whether the strengths are pregressing properly.

How many sets are required will depend upon the Engineers requirements and the importance of and confidence in the concrete. A starting point may be a set of cubes every 3rd load, relaxing this with the Engineers consent when a good pattern of results has been established.

I need cube results for stripping formwork – is this the same procedure?

More or less. The concrete cubes are made in the same way but should be additional to and separate from the quality control cubes. The stripping cubes should be kept at the same ambient temperature as the shuttered concrete until they’re taken to our laboratory. If you tell us your requirements, we will then cure them in a similar way until we start crushing them.

pdf icon. download how to guide

What next?

We hope that this gives you a basic understanding of concrete cube procedures. If you would like more information or would like to arrange for us to make or collect your cubes, please call us or follow the links below;


Concrete Cube Collection and Test Request Form

Request for concrete cube making or collection

What to do in the event of cube failures

Monitoring of concrete pours

Workability (slump) tests

If not done properly can mean costs and losses to your business due to delay, further investigation, possible litigation process or removal and replacement of faulty concrete.
Contact us now

01405 860905