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

The primary purpose of bull floating is to level ridges and fill voids left by screeding, while also embedding coarse aggregate particles just below the surface. This process prepares the slab for subsequent finishing operations like edging, jointing, and troweling.

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

When the surface of fresh concrete sets or seals before the underlying concrete, rising bleed water and entrapped air can get trapped beneath the densified surface. Finishing operations, especially troweling, can exacerbate this, causing blisters or larger delaminated areas.

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

ACI recommends that the depth of a saw-cut or tooled contraction joint should be at least one-quarter (1/4) of the slab thickness. For a 6-inch slab, this calculates to 1.5 inches (6 inches / 4 = 1.5 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

For exterior surfaces exposed to weather, a hard, smooth trowel finish can be very slippery when wet. A light broom finish is applied after floating (and sometimes a single trowel pass) to create a slip-resistant texture, which is crucial for safety on sidewalks, patios, and driveways.

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

Plastic shrinkage cracks occur when the rate of moisture evaporation from the surface exceeds the rate at which bleed water rises to the surface. This condition is most common on hot, dry, and windy days, causing the surface to shrink and crack before it has hardened.

ACI (American Concrete Institute Certification) Practice Test

ACI (American Concrete Institute Certification) Practice Test

ACI Concrete Flatwork Finishing Questions and Answers