ACI Concrete Finishing Defects & Troubleshooting Flashcards

Crazing in a concrete surface is best described as:

Answer: A network of fine random cracks confined to the surface mortar

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

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

Answer: Rapid drying of the surface before the concrete has set

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

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

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

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

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

Answer: 0.20 lb/ft²/hr

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

Bleed water rises to the surface of fresh concrete because:

Answer: Heavier cement and aggregate particles settle, displacing mix water upward

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

Finishing concrete before bleed water has evaporated traps water under the surface, leading to:

Answer: Delamination and scaling during service

Entrapment of bleed water creates a weak, porous plane just below the surface that later separates under traffic or freeze-thaw action.