ACI Flatwork Placement & Leveling 2

Question 1

When placing concrete in hot weather (above 90°F), which practice best prevents rapid moisture loss during flatwork placement?

Accepted Answer

Use sunshades, windbreaks, and mist the subgrade before placement

Answer

Sunshades, windbreaks, and pre-moistened subgrade reduce evaporation rate and prevent premature surface drying during hot-weather placement.

Question 2

What is the primary purpose of using a highway straightedge (10-foot screed) during flatwork leveling?

Accepted Answer

To detect and remove high and low spots across the slab

Answer

A highway straightedge spans across the slab to identify and correct high and low spots, ensuring a flat, even surface.

Question 3

During concrete placement, why should concrete not be moved horizontally with a vibrator?

Accepted Answer

It causes segregation of aggregates and weakens the concrete

Answer

Moving concrete horizontally with a vibrator causes aggregate segregation, pushing coarse particles away and creating weak zones in the slab.

Question 4

What does 'F-number' (FF/FL) system measure in flatwork?

Accepted Answer

Flatness and levelness of the slab surface

Answer

The F-number system uses FF (flatness) and FL (levelness) values to quantify surface tolerance and waviness of concrete floors.

Question 5

Which condition indicates the concrete surface is ready for bull float finishing after screeding?

Accepted Answer

Surface water (bleed water) has completely evaporated

Answer

Bull floating should begin after initial bleed water disappears so the tool does not trap water beneath the surface, which would weaken it.

(ACI) American Concrete Institute Concrete Finisher Practice Test