ACI Certification Concrete Flatwork Finishing 2

Question 1

What is the recommended minimum thickness for a concrete slab-on-grade used in a residential garage, per ACI 302.1R?

Accepted Answer

4 inches (100 mm)

Answer

ACI 302.1R recommends a minimum 4-inch (100 mm) thickness for residential garage slabs; thinner slabs are prone to cracking under vehicle loads.

Question 2

What is 'bleed water' in fresh concrete, and why must flatwork finishers wait for it to evaporate before finishing?

Accepted Answer

Excess mix water that rises to the concrete surface; finishing before it evaporates traps water beneath the surface and weakens the wear layer

Answer

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.

Question 3

When cutting contraction joints in a concrete flatwork slab, what is the recommended joint depth relative to slab thickness?

Accepted Answer

One-quarter (1/4) of the slab thickness

Answer

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.

Question 4

What type of surface finish is produced by dragging a burlap or broom across freshly screeded concrete, and where is it most commonly specified?

Accepted Answer

A broom or burlap-drag finish, commonly specified for exterior flatwork such as sidewalks, driveways, and ramps to provide slip resistance

Answer

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.

Question 5

What is 'curling' (or warping) in concrete slabs, and what is its primary cause?

Accepted Answer

Upward or downward bending of slab edges due to differential shrinkage between the top and bottom of the slab

Answer

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.

ACI (American Concrete Institute Certification) Practice Test

ACI (American Concrete Institute Certification) Practice Test

ACI Certification Concrete Flatwork Finishing 2