ACI ACI Concrete Finishing Defects & Troubleshooting 2

Question 1

Crazing in a concrete surface is best described as:

Accepted Answer

A network of fine random cracks confined to the surface mortar

Answer

Crazing is a map-cracking pattern of very fine surface cracks that do not penetrate deeply into the slab.

Question 2

What is the most common cause of crazing in concrete flatwork?

Accepted Answer

Rapid drying of the surface before the concrete has set

Answer

Rapid surface drying shrinks the paste-rich surface layer faster than the body of the slab, producing the characteristic map-crack pattern.

Question 3

Surface bug holes (voids) on formed concrete walls are primarily caused by:

Accepted Answer

Air trapped against the form face that was not released during vibration

Answer

Bug holes form when air pockets trapped between the fresh concrete and the form surface are not released by adequate vibration.

Question 4

ACI recommends that protective measures against plastic shrinkage cracking should begin when the evaporation rate exceeds:

Accepted Answer

0.20 lb/ft²/hr

Answer

ACI 305R states that when the evaporation rate exceeds 0.20 lb/ft²/hr, precautions such as windbreaks, sunshades, or evaporation retarders are required.

Question 5

Bleed water rises to the surface of fresh concrete because:

Accepted Answer

Heavier cement and aggregate particles settle, displacing mix water upward

Answer

Bleeding is the natural settlement of solid particles under gravity, which displaces mix water upward to the surface.

(ACI) American Concrete Institute Concrete Finisher Practice Test

(ACI) American Concrete Institute Concrete Finisher Practice Test

ACI ACI Concrete Finishing Defects & Troubleshooting 2