Concrete Flatwork Finishing Flashcards
6 cards from real ACI Certification practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 6 Concrete Flatwork Finishing flashcards as text
What is the recommended minimum thickness for a concrete slab-on-grade used in a residential garage, per ACI 302.1R?
Answer: 4 inches (100 mm)
ACI 302.1R recommends a minimum 4-inch (100 mm) thickness for residential garage slabs; thinner slabs are prone to cracking under vehicle loads.
What is 'bleed water' in fresh concrete, and why must flatwork finishers wait for it to evaporate before finishing?
Answer: Excess mix water that rises to the concrete surface; finishing before it evaporates traps water beneath the surface and weakens the wear layer
Bleed water migrates upward through the paste; finishing while bleed water is present dilutes the surface paste, reducing surface strength and causing scaling and dusting of the finished slab.
When cutting contraction joints in a concrete flatwork slab, what is the recommended joint depth relative to slab thickness?
Answer: One-quarter (1/4) of the slab thickness
ACI 302.1R recommends saw-cutting contraction joints to a depth of at least one-quarter (1/4) the slab thickness to create a plane of weakness that controls where cracking occurs.
What type of surface finish is produced by dragging a burlap or broom across freshly screeded concrete, and where is it most commonly specified?
Answer: A broom or burlap-drag finish, commonly specified for exterior flatwork such as sidewalks, driveways, and ramps to provide slip resistance
Broom or burlap-drag textures create surface ridges that improve traction on wet surfaces, which is why exterior flatwork that must handle foot and vehicle traffic requires this type of finish.
What is 'curling' (or warping) in concrete slabs, and what is its primary cause?
Answer: Upward or downward bending of slab edges due to differential shrinkage between the top and bottom of the slab
Curling occurs when the top of the slab dries and shrinks faster than the bottom, causing edges to lift (upward curling) or curl downward depending on the moisture gradient direction.
What is the purpose of placing a vapor retarder directly beneath an interior concrete slab-on-grade?
Answer: To prevent moisture transmission from the subgrade through the slab into the building interior, protecting floor coverings and occupant comfort
A vapor retarder (e.g., 10-mil polyethylene film) limits moisture vapor transmission from soil beneath the slab, preventing moisture-related failures of adhesive-bonded flooring, hardwood, and carpet.