ACI Surface Preparation & Finishing Techniques 2

Question 1

What is the primary purpose of screeding concrete after placement?

Accepted Answer

To strike off excess concrete and establish grade

Answer

Screeding strikes off excess concrete and brings the surface to the desired grade or elevation.

Question 2

Which finishing tool is used immediately after screeding to embed aggregate and bring mortar to the surface?

Accepted Answer

Bull float

Answer

A bull float is used right after screeding to embed coarse aggregate and bring cement paste to the surface.

Question 3

When should a finisher begin hand floating operations?

Accepted Answer

When the bleed water sheen has disappeared and the surface can support a finisher's weight

Answer

Hand floating begins when surface bleed water has evaporated and the concrete is firm enough to support a finisher without excessive indentation.

Question 4

What defect results from troweling concrete before bleed water has evaporated?

Accepted Answer

Delamination

Answer

Troweling too early traps bleed water under the surface, causing delamination where the top layer separates from the base.

Question 5

In which direction should a darby or bull float be pushed across fresh concrete?

Accepted Answer

In overlapping arcs, keeping the leading edge slightly raised

Answer

Darbies and bull floats are worked in overlapping passes with the leading edge slightly raised to avoid digging into the surface.

(ACI) American Concrete Institute Concrete Finisher Practice Test