Concrete Testing - How Often Should It Be Done?
If ever you’ve asked a materials testing specialist this same question, you’ll know that their response has only succeeded in creating even more confusion. The reason for this is that concrete is a very complex subject and there loads of different factors and conditions that must be taken into account.
The following article seeks to identify the various concrete testing methods in use today and the frequency in which the tests should be conducted.
This test is ideally conducted prior to having the concrete laid. The purpose of this test is to calculate the consistency of fresh concrete, specifically the amount of water and cement present throughout. There are 3 possible outcomes to a slump test:
Collapsed Slump – if your test sample completely caves in while setting, it means that there’s too much water in the mix.
Shear Slump – if your test collapses down one side, the result is deemed ambiguous and the mix test will need to be restarted.
True Slump – if your sample is able to maintain its original form (there will be some unavoidable, albeit minor slumping), then the mix is deemed satisfactory and is classed as a true slump.
Air Content Test
This simply determines the amount of air contained within your concrete sample and should be conducted before the concrete is laid. This test is particularly significant for concrete that is likely to be subjected to de-icing salts. For such concrete, it’s important that microscopic air bubbles are present to help the concrete maintain its strength while water becomes frozen and expands the concrete from within. Air content tests are conducted on multiple occasions throughout the building process to guarantee compliance with required regulations.
This is best conducted before the concrete is laid. This merely involves inserting a thermometer around 2 to 3 inches deep, within a concrete test sample. Concrete temperature is an essential measurement, as it indicates how strong it will be when it finally sets.
Compressive Strength Test
This test determines the amount of pressure that can be exerted upon a concrete sample, before it fails. The compressive strength of concrete depends on a range of factors, as determined by the structural engineers.
How regularly should these concrete tests be conducted?
The specific qualities of a particular concrete mix will decide the frequency and type of tests that will be required to be performed by a qualified concrete testing company. Here is a general guide for how often each concrete test should be conducted throughout the building process.
As this test calculates the consistency and usefulness of new concrete mix, the test is required to be performed for each individual structural sample. It also needs to be conducted every time a compressive strength test is done and in situations where the composition may have altered.
Air Content Test
This test is required to be done for each individual structural sample. The frequency that concrete should be subjected to the air content test differs throughout the building process. The test is conducted on the first 3 sets of concrete and is done so until 3 successive sets result in satisfactory air content values. From here, every 5th set needs to be tested after the 3rd successive value has been taken. If a set of concrete is discovered to possess qualities that are below the structural requirements, then testing should return to the initial rule of three.
This test is vital for deciding if additional tests can be performed, including the calculation of preliminary curing strength of concrete test samples. For instance, if environmental conditions are particularly warm, then a cooling apparatus may be required to ensure a curing temperature that falls within the acceptable range, thus allowing strength based tests to be conducted.
Compressive Strength Test
This test should be performed a minimum of one for every 100 m3 concrete laid, or a minimum of one test a day, per concrete mix. This is a standard, but some projects may demand more regular compressive strength testing.
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