Cube Testing: The Silent Guardian of Concrete Quality
Asking a site engineer about the questions which trouble them prior to concrete slab pouring will most likely bring up "will the concrete hold?" This is the very question which has prompted cube testing. Having worked on site for ten years and reviewed multiple lab reports, I can safely state that no other quality control measure is as important in concrete construction as this one.
What Does Cube Testing Tell?
To put it bluntly, cube testing involves measuring compressive strength of concrete through casting it into molds of certain sizes, curing those molds and then applying pressure to them with a hydraulic press to get the load at which the mold will break down. Depending on the type of concrete being tested, it might have compressive strength of M20, M25 or any other grade required for structural column.
It sounds simple enough, but it is very important indeed. Failing to pass this test can be a sign that your concrete is not strong enough and needs to be reworked.
Any civil engineer should know this by heart – the cube test formula involves dividing the load at which the cube has broken down by the area of the cube face. This area does not change for standard 150mm cubes, so you just plug your figures into the formula and get compressive strength of your concrete sample in N/mm² or MPa.
Following the Code, Not Using Guesswork
None of these numbers are useful without standardized tests, which is where cube test IS code becomes important. In India, IS 516 code defines all parameters of your cube test – from dimensions of the mold to loading rate and curing time. Ignoring or misunderstanding this code is one of the most frequent mistakes made on the construction sites due to rushed schedule of concrete pouring.
The Machines to Do the Job
None of it can be done without reliable machinery, though. Properly calibrated cube testing machine will make sure that the loading rate will remain the same throughout the test as defined by IS 516 code. Even slightest deviation of this parameter can affect the results and give the wrong reading of concrete strength. Calibration tests are essential for these machines.
Curious Case of the Hidden Cube Test
A phrase that frequently confuses new engineers is the hidden cube test, whereby sample cubes are poured and cured at the job site in real world conditions and tested at a later stage. It may be a little used test, but certainly a very useful one, especially for large scale infrastructural projects where laboratory-cured specimens do not paint the whole picture.
Concrete cube testing is not merely a requirement on a quality assurance checklist, it is the line between certainty and speculation in the construction business. Do things correctly and you'll not only meet the regulations, you'll be building for the future.
