I have been in 13 years in the quality assurance and quality control field and I already experienced about concrete works on site. How it will be cast? How it will be cured? And how it will be placed? The most important aspect of concrete is “How it will be checked and eventually be tested?” You as a quality engineer should know about these quality tests of concrete.
By the way, before we go farther, I will give the most common meaning of concrete.
“Concrete is a composite material that consists essentially of a binding medium within which are embedded particles or fragments of aggregates, usually a combination of fine aggregates and coarse aggregates; in Portland-cement concrete, the binder is a mixture of a Portland-cement and water, with or without admixtures.”
In order to determine the quality of concrete on site, it shall undergo quality tests. Here are 6 common quality tests on concrete before and after completion of casting on site.
1. Slump test before leaving the batching plant and on arrival on site
This is to determine the workability of concrete in terms of slump test. After batching the concrete, a sample of fresh concrete shall be taken to test for slump tests and the samples for compressive strength test be taken too. This is to make sure that the batched concrete is complying with the mix design before it’s released from the batching plant.
Upon arrival on site, a sample of fresh concrete shall be tested with slump test again, but temperature shall be checked with the calibrated thermometer beforehand. Three cubes or cylinders of samples shall be taken for compressive strength tests, these will be the samples from the site.
You might ask “What is a slump?” And “Why there is plus or minus sign (+/-) in the slump?” You may go ahead with this article The definition of construction terms to see the meaning of slump. The plus or minus sign is the symbol of tolerance of slump. Let say for example the slump of approved concrete design mix for your suspended slab is 150 mm +/- 25. It means that the drop of concrete after the slump cone is removed should not be more than 175 mm nor less than 125 mm.
2. Compressive strength test (this a common quality tests of concrete)
Three samples of cubes or cylinders shall be taken for compressive strength test, but it is not commonly three samples, sometimes it is two depending on the specification. You might ask why sometimes, is there an extra of one sample? Good that you asked. This one sample extra shall be tested “if!” the two cubes or cylinders samples are tested from the three and if it is failed and the remaining sample is passed. If the consultant is not satisfied with the result (definitely not!) and he wishes to test the extra one. It shall be tested in 60 days.
You might ask why again, because if the concrete cube fails at 28 days the concrete cubes might be having a slow gaining strength, but the required strength might be achieved after 60 days, especially those concrete having pozzolanic cement and cement replacement that has GGBS and FA.
So don’t forget to save extra samples.
3. Water Permeability test
A water permeability test is one of the tests to determine the durability of concrete. Three cubes shall be taken from fresh concrete and tested in accordance with the German Standard DIN 1048 at 28 days age. This kind of test shall be taken from substructures concrete elements like foundations, concrete water tank, retaining wall, etc. The frequency of the water permeability test can be found in this article The Frequency of Various Tests.
4. Rapid Chloride Ion Penetration Test
Like water permeability test, this is also one of the tests to determine the durability of concrete. Three cubes shall be taken from fresh concrete delivered on site and tested at 28 days age. The test shall be done in accordance with ASTM C1202-97.
5. Water Absorption Test
Here is the other test that would determine the durability of concrete. The three cube samples shall be taken from the delivered fresh concrete and kept it in the curing tank for 28 days or after 24 hours the concrete sample would be demoulded and it will be sent directly to the approved third-party laboratory to ensure its curing. The size of the cube sample is 150 mm and tested in accordance with BS 1881-122.
6. Initial Surface Absorption Test
Three cubes samples shall be taken from the fresh concrete delivered on site. It shall be cured and placed inside the curing tank for 28 days prior to testing. The sample is to be tested in accordance with BS 1881-208.
The water permeability test, Rapid Chloride Ion Penetration test, water absorption test, and the initial surface absorption test tests to determine the durability of concrete. To determine its ability to resist weathering action, chemical attack and any process of deterioration.
If you have supplements on the above concrete test of concrete you can write on the comment box below.