KNOW YOUR CONRETE TESTS

Users of readymix concrete don’t always realize that unless otherwise specified, readymix suppliers only test process control tests for their own purposes and users should always specify further tests if that is required for their own purposes.

professionals know that here is a vast difference between process control testing and testing to meet specifications on site. As a norm readymixers take samples at the plant and not necessary at the point of discharge and only one out of every one hundred cubes are tested.

However, SANS specifications says that for testing concrete to SANS specifications, sampling fresh concrete should be carried out in the middle of a pour per mixer. This must be specified by the user though and if specified must be sampled from the middle 70% of the truck.

Specifications count

If the user does not specify SANS quality readymix then there is no real measure of the concrete being delivered. If nothing is specified then it also does not have to be done, that is why it is important to specify the concrete properties, as well as testing and sampling methods to be used.

In the event of a failure, it has got to be established where the failure occurred, either material, test or specification failure. Remember, the specification must be measurable for any finding to be made if a claim were to arise.

For example, investigators will ask what was specified and how was this specification contravened? It has got to be fit for purpose so even if it is 30Mpa in terms of strength specification but is not workable or pourable (as required on site) and this was not specified, then the specification failed, not the concrete.

Word of warning

The following five critical points need to be considered for the correct testing to be undertaken:

1. What is specified?
2. What are the acceptance criteria?
3. Who is going to do the testing?
4. Find agreement of testing methods etc before the project starts.
5. Plan to test, you must plan how, where and when testing takes place.

What is important to know is that a test has many facets and for the test to be accepted every one of these must be done according to SANS criteria. If any one of these is not done then one cannot determine the influence of any small inconsistency, so the outcome of the whole test cannot be used.

Nor can it be proved what the result of a small inconsistence will have on the end result of the test. Therefore, everything needs to be done according to the agreed specification. This highlights the importance of all parties agreeing upfront to a testing regimen that is acceptable to all the parties involved in a construction project and that is in accordance with SANS specifications.”