Category: Structure & materials
Prepared by Eng. Ahmed Fathy, Projects Manager ·
Definition
The cube test takes fresh concrete during the pour in 150 mm cube moulds, cures them in water, then crushes them in the lab at 7 and 28 days to measure compressive strength against the required grade. The specification sets the number of samples by pour volume.
Why it matters on a project
It is the formal proof that the placed concrete reaches the required strength. Low results mean more testing, strengthening or demolition.
Measurement and pricing
Priced per set or per cube in the lab contract, within testing under indirect costs.
Worked example
Grade C30/37, so 37 MPa on cubes, with three 28-day results of 40, 38 and 41: average (40 + 38 + 41) ÷ 3 = 39.7 MPa, above 37; the lowest result is then checked against the specification limit.
Common mistake
Leaving cubes in the sun without curing in the first days, so results come out low even though the concrete is sound.
Frequently asked questions
Why crush samples at 7 days?
To give an early indication of strength; final acceptance is on 28-day results.
How do cubes differ from cylinders?
150 mm cubes are common in Saudi Arabia and British specifications, cylinders in American ones, and their results are not equal.
Related terms
- Concrete grade (compressive strength)The characteristic compressive strength of concrete at 28 days, e.g. C30 or 300 kg/cm².
- Slump testA simple site test measuring the consistency and workability of fresh concrete.
- Concrete core testDrilling cylinders from hardened concrete to measure its actual strength.
- Third-party inspectionIndependent testing by an accredited body separate from contractor and owner.
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