ACI Concrete Flatwork Finishing Questions and Answers

Question 1

A concrete finisher is preparing to perform the initial floating of a freshly placed slab. Which of the following is the primary purpose of bull floating?

Accepted Answer

To embed large aggregate, level the surface, and remove screed marks.

Answer

To create a smooth, dense, hard-troweled surface.

Answer

To open the surface to allow bleed water to evaporate quickly.

Answer

To cut control joints to a depth of one-quarter the slab thickness.

Question 2

While finishing a concrete slab on a hot, windy day, the finisher notices the surface is drying and crusting over much faster than the underlying concrete. Continuing to trowel under these conditions is likely to cause which surface defect?

Accepted Answer

Blistering or delamination

Answer

Crazing

Answer

Scaling

Answer

Discoloration

Question 3

According to ACI standards, what is the proper depth for a saw-cut contraction joint in a 6-inch thick slab-on-ground?

Accepted Answer

At least 1 1/2 inches

Answer

At least 1/2 inch

Answer

At least 1 inch

Answer

At least 2 inches

Question 4

A finisher is working on an exterior slab that will be exposed to freeze-thaw cycles. After the bleed water has evaporated and the surface has been floated, what is the most appropriate next step to ensure durability without creating a dangerously slick surface?

Accepted Answer

Immediately cover the slab with plastic sheeting.

Answer

Perform multiple hard trowel passes with a steel trowel.

Answer

Apply a dry shake hardener and trowel it into the surface.

Answer

Provide a light broom finish.

Question 5

Which of the following conditions is most likely to cause plastic shrinkage cracks to form on the surface of freshly placed concrete?

Accepted Answer

High wind speed and low humidity.

Answer

Low ambient temperature and high humidity.

Answer

Heavy rain during placement.

Answer

Finishing operations beginning too late.

Question 6

To achieve a dense, smooth, and wear-resistant surface on an interior concrete floor, when should the first troweling operation begin?

Accepted Answer

After the bleed water has evaporated and the concrete can support the finisher's weight with only a slight indentation.

Answer

Immediately after bull floating, while the concrete is still soft.

Answer

After the concrete has reached its final set.

Answer

While bleed water is still visible on the surface.