Joint Layout & Crack Control Flashcards
7 cards from real ACI practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Joint Layout & Crack Control flashcards as text
In hot weather concrete work, which action best reduces the risk of plastic shrinkage cracking before finishing is complete?
Answer: Using an evaporation retarder on the concrete surface
Evaporation retarders form a thin monomolecular film on the concrete surface that slows moisture loss during the finishing window.
The joint sealant placed in a control joint after curing is intended to:
Answer: Prevent water and incompressibles from entering the joint
Joint sealant keeps moisture and debris out of the joint, protecting the sub-base and preventing incompressible materials from restricting slab movement.
According to ACI guidelines, the maximum joint spacing for a 5-inch thick unreinforced concrete slab is approximately:
Answer: 10 feet
ACI 360R recommends contraction joint spacing of no more than 24–30 times the slab thickness in inches, placing a 5-inch slab at roughly 10–12.5 feet.
What is the main reason for greasing or sleeving one end of a dowel bar at a contraction joint?
Answer: To allow the slab to move horizontally while still transferring vertical loads
The lubricated or sleeved end can slide freely so the slab panel can contract and expand without restraint while vertical (shear) loads are still transferred.
A slab that receives heavy forklift traffic should have contraction joints spaced:
Answer: Closer together to keep panels smaller and reduce curling stresses
Closer joint spacing reduces panel size, limiting curling and warping that can cause joint edges to chip under repeated forklift loading.
Which type of crack typically runs diagonally from the corner of a slab panel toward the interior?
Answer: Corner crack caused by excessive panel length-to-width ratio
Panels with a high length-to-width ratio (greater than 1.5:1) tend to develop diagonal corner cracks because shrinkage stress concentrates at the corners.
When a contraction joint is placed adjacent to a column, what additional joint type is typically required around the column itself?
Answer: An isolation joint to allow independent column movement
An isolation joint around a column allows the slab to move independently from the column, preventing cracking where two structures with different settlements or movements meet.