A residential foundation in Hawaii requires concrete with a minimum compressive strength of 2,500 psi. If the concrete cylinder test results show 2,350 psi at 28 days, what action should be taken?
Correct Answer
C) Reject the concrete and require remedial action
Concrete that fails to meet the specified minimum compressive strength must be rejected and remedial action taken, as there is no acceptable tolerance below the specified minimum.
Why This Is the Correct Answer
Concrete that fails to achieve the specified minimum compressive strength at 28 days must be rejected and remedial action taken. There is no code-acceptable tolerance below the specified minimum — 2,350 psi is a failing result when 2,500 psi is specified. Remedial actions may include core sampling, load testing, or removal and replacement.
Why the Other Options Are Wrong
Option A: Accept the concrete as it's within 5% tolerance
There is no '5% tolerance' allowance in concrete compressive strength specifications. The 2,500 psi figure is a minimum, not a target with a tolerance band. Accepting substandard concrete on the assumption of a tolerance that does not exist is a code violation.
Option B: Reduce the design load on the foundation
Reducing the design load does not correct the concrete's deficiency and is not a standard code response to a failed cylinder test. The structure must be built to design specifications, not redesigned around failing materials.
Option D: Test additional cylinders for verification
Testing additional cylinders for verification can be a step in the investigation process but is not the required immediate action when results clearly show 2,350 psi vs. a 2,500 psi minimum. The primary action is rejection and remediation, not simply gathering more data.
Memory Technique
Below minimum = Reject. No tolerance, no negotiation. Think of the 28-day test as a pass/fail exam — if the number is below spec, the concrete fails, full stop.
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