ACI Subgrade & Base Preparation for Slabs Flashcards

Per ACI 318, the minimum concrete cover required for reinforcing steel in a slab-on-grade not exposed to weather is:

Answer: 3/4 inch

ACI 318 specifies 3/4-inch minimum cover for slabs not exposed to weather or ground, protecting the steel from corrosion.

When welded wire reinforcement (WWR) is used in a slab-on-grade primarily to control shrinkage cracking, it should be positioned:

Answer: In the upper one-third of the slab thickness

Shrinkage cracks initiate at the surface, so placing WWR in the upper third maximizes its effectiveness in restraining crack opening.

For light industrial floor slabs, ACI 360R suggests a minimum slab-on-grade thickness of:

Answer: 5 to 6 inches

ACI 360R recommends 5 to 6 inches as a practical minimum for light industrial use to handle typical forklift and storage loads.

According to ACI, control joints in slabs on grade should be saw cut to a minimum depth of:

Answer: One-quarter of the slab thickness

A saw cut depth of T/4 (one-quarter the slab thickness) creates a weakened plane that guides cracking to the joint location.

Synthetic fiber reinforcement added to concrete flatwork primarily serves to:

Answer: Reduce plastic shrinkage cracking during the early hours after placement

Synthetic fibers act as secondary reinforcement while concrete is still plastic, bridging micro-cracks before the concrete sets.

Reinforcing bars and welded wire reinforcement placed in slabs on grade must be supported by chairs or bolsters to ensure:

Answer: Proper cover is maintained during concrete placement and consolidation

Chairs hold reinforcement at the specified elevation so that concrete placement and vibration do not displace it, maintaining code-required cover.