ACI ACI Concrete Finishing Defects & Troubleshooting

Question 1

What is the primary cause of scaling on concrete surfaces exposed to freeze-thaw cycles?

Accepted Answer

Using deicing chemicals on concrete with low air entrainment

Answer

Over-vibrating the concrete during placement

Answer

Using too much coarse aggregate in the mix

Answer

Finishing the concrete too late

Question 2

Surface dusting of a concrete floor is most commonly caused by which finishing error?

Accepted Answer

Troweling the surface while bleed water is still present

Answer

Using too coarse a broom for the final texture

Answer

Applying the second trowel pass too late

Answer

Over-curing the slab with water

Question 3

Delamination of a concrete slab surface occurs because:

Accepted Answer

Air or bleed water becomes trapped beneath a prematurely sealed surface

Answer

The slab was cured too quickly with a curing compound

Answer

Too much coarse aggregate was used near the top

Answer

The concrete was placed at too high a slump

Question 4

According to ACI, what finishing action most frequently leads to delamination in flatwork?

Accepted Answer

Finishing the surface before bleed water has evaporated

Answer

Using a bull float before screeding

Answer

Applying the curing compound before final troweling

Answer

Placing concrete directly on a dry subgrade

Question 5

Which of the following best describes the ACI definition of surface scaling?

Accepted Answer

Peeling or flaking of the near-surface mortar layer

Answer

Random shallow cracks across the slab

Answer

White salt deposits on the surface

Answer

Loss of surface paste due to abrasion

Question 6

Plastic shrinkage cracking differs from drying shrinkage cracking primarily because it occurs:

Accepted Answer

Before the concrete has achieved initial set

Answer

After the concrete has fully hardened

Answer

Only in slabs thicker than 6 inches

Answer

Only when calcium chloride is used