The testing agency molds 6 by 12 in. cylinders from one concrete sample for a normal compressive strength test. ACI 318 defines the test result as what?
Correct Answer
D) The average strength of at least two 6 by 12 in. cylinders made from the same sample and tested at the same age.
ACI 318-19 26.12.1 defines a strength test for 6 by 12 in. cylinders as the average strength of at least two cylinders made from the same sample and tested at the same age. Other choices: using the highest break, one cylinder, or forcing the three-cylinder rule onto 6 by 12 in. cylinders misstates the ACI definition.
Why This Is the Correct Answer
ACI 318-19 26.12.1 defines a strength test for 6 by 12 in. cylinders as the average strength of at least two cylinders made from the same sample and tested at the same age.
Why the Other Options Are Wrong
Option A: The highest cylinder break from the sample
Choice A gives The highest cylinder break from the sample. Its specific error: the option does not produce the required Strength testing outcome, The average strength of at least two 6 by 12 in.
Option B: Make one randomly selected cylinder break the answer for strength testing, leaving strength testing unverified
Choice B (One randomly selected cylinder break.) is rejected because it points to One randomly selected cylinder break. but.
Option C: Limit strength testing to the average of any three cylinders only
In concrete work, The average of any three cylinders only. is the wrong selection for Strength testing: it leaves the work at an informal or incomplete stage, while Strength testing requires The average strength of at least two 6 by 12 in.
Memory Technique
Treat strength testing like a labeled shelf; only the matching condition belongs with The average strength of at least two 6 by 12 in. cylinders made from the same sample and tested at the same age.
Reference Hint
Open ACI 318-19, Building Code Requirements for Structural Concrete; use ACI 318-19 26.12.1 to confirm that ACI 318-19 26.12.1 defines a strength test for 6 by 12 in.
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