ACI Concrete Finishing Defects & Troubleshooting Flashcards

Blistering of a concrete slab surface is caused by:

Answer: Air or bleed water trapped under a surface that has been prematurely sealed by troweling

Blisters form when gas or bleed water trapped beneath a dense, troweled surface layer cannot escape, creating raised bubbles.

How does map cracking (crazing) differ from structural cracking?

Answer: Map cracking is confined to the surface mortar and does not affect structural integrity

Crazing involves only the thin surface mortar layer and has no structural significance, though it may affect appearance and durability.

Concrete discoloration is most commonly associated with which of the following?

Answer: Uneven curing or the use of calcium chloride admixtures

Calcium chloride can darken concrete, and uneven curing creates moisture gradients that result in patchy color variations.

Efflorescence on a concrete surface is the result of:

Answer: Water-soluble salts carried to the surface and deposited as water evaporates

Efflorescence is a white, powdery deposit left when water migrates through concrete, dissolves soluble salts, and evaporates at the surface.

Surface popouts in concrete flatwork are most often caused by:

Answer: Reactive aggregate particles absorbing moisture and expanding near the surface

Popouts occur when a reactive or frost-susceptible aggregate particle near the surface absorbs water, expands, and breaks off a cone of concrete.

To prevent blistering during power troweling, the finisher should:

Answer: Wait until the concrete has reached proper stiffness and bleed water has fully evaporated before closing the surface

Blistering is prevented by not sealing the surface until the concrete is ready — all bleed water must be gone and the mix stiff enough to support finishing.