A wall form has tight reinforcement, and the concrete supplier asks for the maximum nominal aggregate size allowed by ACI proportioning limits. Which set of limits governs?
Correct Answer
A) Not more than one-fifth the narrowest form dimension, one-third the slab depth, or three-fourths the minimum clear spacing between reinforcement
ACI 318-19 26.4.2.1 limits nominal maximum aggregate size to the smallest of one-fifth the narrowest dimension between forms, one-third the slab depth, and three-fourths the minimum clear spacing between reinforcement. Other choices: the one-half limits are too permissive, one inch is not universal, and pumpability does not override the code limit.
Why This Is the Correct Answer
ACI 318-19 26.4.2.1 limits nominal maximum aggregate size to the smallest of one-fifth the narrowest dimension between forms, one-third the slab depth, and three-fourths the minimum clear spacing between reinforcement.
Why the Other Options Are Wrong
Option B: Not more than one-half the narrowest form dimension, one-half the slab depth, or the full clear spacing between bars
In concrete work, Not more than one-half the narrowest form dimension, one-half the slab depth, or the full clear spacing. is the wrong selection for Aggregate size: the option does not produce the required Aggregate size outcome, Not more than one-fifth the narrowest form dimension, one-third the slab depth, or three-fourths the.
Option C: Exactly one inch for all reinforced concrete
The trap in C is Exactly one inch for all reinforced concrete. That selection is wrong because it describes work from another assembly, while the Aggregate size item is asking for Not more than one-fifth the narrowest form dimension, one-third the slab depth, or three-fourths.; Nominal maximum aggregate size is capped by 1/5 form dimension, 1/3 slab depth, and 3/4 clear reinforcement spacing.
Option D: The largest aggregate the pump can move without plugging
Choice D gives The largest aggregate the pump can move without plugging. Its specific error: the action skips the timing, documentation, or field-control step needed for Aggregate size.
Memory Technique
Treat aggregate size like a labeled shelf; only the matching condition belongs with Not more than one-fifth the narrowest form dimension, one-third the slab depth, or three-fourths the minimum clear spacing.
Reference Hint
Open ACI 318-19, Building Code Requirements for Structural Concrete; use ACI 318-19 26.4.2.1 to confirm that ACI 318-19 26.4.2.1 limits nominal maximum aggregate size to the smallest of one-fifth the narrowest dimension between forms, one-third the slab depth, and three-fourths the minimum clear spacing between reinforcement.
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