How the Cube Test Register works
Record concrete cube test results for your site and check them against IS 456 acceptance criteria. Enter the crushing loads of each set of three 150 mm cubes; the register converts them to N/mm², checks the 15% variation rule and tells you whether the 28-day results meet Table 11.
Frequently asked questions
How do you calculate cube compressive strength?
Strength (N/mm²) = load in kN × 1000 / (150 × 150) for a 150 mm cube. A load of 562.5 kN therefore gives 25 N/mm².
What are the acceptance criteria for concrete cubes as per IS 456?
For M20 and above, the mean of 4 non-overlapping consecutive results must be at least fck + 0.825 × standard deviation or fck + 4 N/mm², whichever is greater, and each individual result at least fck − 4 N/mm² (Table 11). For M15 the margins are 3 N/mm².
When is a cube test result invalid?
A test result is the average of three cubes. If any cube differs from that average by more than 15%, the result is treated as invalid (IS 456 cl. 15.4).
What strength should concrete reach at 7 days?
Typically about 65% of the 28-day strength for OPC concrete. Early-age results are useful for monitoring, but acceptance is based on 28-day results.
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