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

2 inches (50 mm)

Answer

6 inches (150 mm)

Answer

8 inches (200 mm)

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

Water added during consolidation that improves surface hardness

Answer

Chemical admixture water that retards setting time uniformly

Answer

Water introduced by curing compounds applied immediately after screeding

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

One-half (1/2) of the slab thickness

Answer

One-third (1/3) of the slab thickness

Answer

One-eighth (1/8) of the slab thickness

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

A smooth trowel finish for use in industrial warehouse floors

Answer

An exposed aggregate finish for decorative interior applications

Answer

A hardened steel-troweled finish for parking structures

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

Lateral sliding of the slab due to inadequate subbase friction

Answer

Heaving of the slab center caused by expansive subgrade soils

Answer

Horizontal delamination of the surface mortar layer caused by bleed water

Question 6

What is the purpose of placing a vapor retarder directly beneath an interior concrete slab-on-grade?

Accepted Answer

To prevent moisture transmission from the subgrade through the slab into the building interior, protecting floor coverings and occupant comfort

Answer

To increase slab compressive strength by slowing curing

Answer

To prevent upward migration of aggregate during vibration

Answer

To serve as a bond breaker so the slab can slide freely over the subbase