ACI Flatwork Placement & Leveling 3

Question 1

What is the recommended maximum free-fall height when depositing concrete to minimize segregation?

Accepted Answer

3 feet

Answer

ACI guidelines recommend limiting free-fall to no more than 3 feet to prevent coarse aggregate from separating from the mortar.

Question 2

When screedng concrete between forms, the screed should be moved with what motion?

Accepted Answer

A sawing side-to-side motion while advancing forward

Answer

A sawing back-and-forth lateral motion while advancing forward fills voids and levels the surface without leaving ridges.

Question 3

What is 'subgrade drag' and why does it matter during flatwork placement?

Accepted Answer

Friction between the subgrade and concrete slab that can cause cracking as the slab shrinks

Answer

Subgrade drag is the restraint force between the slab and subgrade that resists shrinkage movement, potentially causing cracking if not relieved by joints or proper subgrade preparation.

Question 4

Which type of screed is best suited for large flatwork areas requiring high flatness tolerances (high FF numbers)?

Accepted Answer

Laser-guided or GPS-controlled vibratory screed

Answer

Laser-guided or GPS-controlled vibratory screeds provide the precision and consistency needed to achieve high FF/FL tolerances on large slab areas.

Question 5

When pumping concrete for flatwork, the discharge hose should be positioned to deposit concrete:

Accepted Answer

As close to final position as possible to minimize movement

Answer

Depositing near the final position minimizes the need to rake or move concrete, reducing the risk of segregation and maintaining mix uniformity.

(ACI) American Concrete Institute Concrete Finisher Practice Test

(ACI) American Concrete Institute Concrete Finisher Practice Test

ACI Flatwork Placement & Leveling 3