For a 6000 psi concrete mixture, the superintendent checks the low-test limit in the ACI acceptance criteria. Ignoring the three-test average for a moment, which individual test value is the minimum allowed by that branch?
Correct Answer
C) 5400 psi
ACI 318-19 26.12.3.1 uses a 0.10 f'c limit for specified strengths greater than 5000 psi, so a 6000 psi mix may not have an individual strength test below 5400 psi by that branch. Other choices: 5000 psi and 5200 psi are too low, while 5700 psi is stricter than the ACI 10 percent allowance.
Why This Is the Correct Answer
ACI 318-19 26.12.3.1 uses a 0.10 f'c limit for specified strengths greater than 5000 psi, so a 6000 psi mix may not have an individual strength test below 5400 psi by that branch.
Why the Other Options Are Wrong
Option A: 5000 psi
The trap in A is 5000 psi. That selection is wrong because 5000 psi is a different published number than the cited Strength acceptance value; ACI 318-19 26.12.3.1 supports 5400 psi; For f'c > 5000 psi, the low-test limit is f'c minus 0.10 f'c.
Option B: 5200 psi
Choice B gives 5200 psi. Its specific error: 5200 psi is a different published number than the cited Strength acceptance value; ACI 318-19 26.12.3.1 supports 5400 psi. The accepted answer is 5400 psi.
Option D: 5700 psi
In concrete work, 5700 psi is the wrong selection for Strength acceptance: 5700 psi is a different published number than the cited Strength acceptance value; ACI 318-19 26.12.3.1 supports 5400 psi.
Memory Technique
Use a fastener row memory cue for strength acceptance: the stem's condition unlocks 5400 psi.
Reference Hint
Open ACI 318-19, Building Code Requirements for Structural Concrete; use ACI 318-19 26.12.3.1 to confirm that ACI 318-19 26.12.3.1 uses a 0.10 f'c limit for specified strengths greater than 5000 psi, so a 6000 psi mix may not have an individual strength test below 5400 psi by that branch.
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