A contraction joint is detailed in a slab-on-grade panel. Its primary function is to do what?
Correct Answer
A) Create a planned weakened plane where shrinkage cracking can occur in a controlled line
A contraction joint intentionally weakens a line so shrinkage cracking is controlled at that location. Other choices: it does not thicken the slab, eliminate shrinkage, or automatically serve as a doweled load-transfer construction joint.
Why This Is the Correct Answer
A contraction joint intentionally weakens a line so shrinkage cracking is controlled at that location.
Why the Other Options Are Wrong
Option B: The superintendent should increase slab thickness under rack posts
In concrete work, Increase slab thickness under rack posts is the wrong selection for Control joints: it leaves out the controlling Control joints result: Create a planned weakened plane where shrinkage cracking can occur in a controlled line.
Option C: Eliminate all drying shrinkage in the concrete, leaving control joints unverified
The trap in C is Eliminate all drying shrinkage in the concrete. That selection is wrong because it removes the controlling Control joints requirement instead of meeting it.
Option D: Transfer vertical load the same way a doweled construction joint does
Choice D gives Transfer vertical load the same way a doweled construction joint does. Its specific error: the option does not produce the required Control joints outcome, Create a planned weakened plane where shrinkage cracking can occur in a controlled line.
Memory Technique
Attach control joints to a scope box: remember the function, then the wording Create a planned weakened plane where shrinkage cracking can occur in a controlled line.
Reference Hint
Open The Contractor's Guide to Quality Concrete Construction, 4th Ed., 2018; use the index entry or section for "Slab contraction joints" to confirm that A contraction joint intentionally weakens a line so shrinkage cracking is controlled at that location.
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