NASCLA Accredited Commercial General ContractorConcreteHard
A concrete inspector is on-site observing the placement of reinforcement for a continuous footing. The design drawings specify #6 rebar with a minimum concrete cover of 3 inches. During inspection, the inspector notices some rebar is resting directly on the subgrade. What is the immediate concern, and what corrective action should be taken?
- AConcern: Reduced bond strength. Action: Spray rebar with a bonding agent.
- BConcern: Corrosion and structural inadequacy. Action: Install proper concrete chairs or blocks to achieve cover.
- CConcern: Difficult concrete placement. Action: Increase concrete slump for easier flow.
- DConcern: Increased concrete consumption. Action: Add more aggregate to the mix.
Show answer & explanationAnswer & explanation
Correct answer: B. Concern: Corrosion and structural inadequacy. Action: Install proper concrete chairs or blocks to achieve cover.
Rebar resting on the subgrade means it lacks the specified concrete cover. Insufficient cover exposes the rebar to moisture and oxygen, leading to corrosion, which compromises the structural integrity of the footing. The immediate corrective action is to properly position the rebar using chairs or blocks to achieve the required cover.
Why the other options are wrong
- A. While bond strength can be affected, the primary concern is corrosion. Bonding agents are not a substitute for proper cover.
- C. Increasing slump could weaken the concrete and would not address the fundamental issue of inadequate rebar cover.
- D. Rebar position does not directly impact concrete consumption in a way that adding aggregate would correct; this is an issue of cover.
Concrete Cover for Rebar
The distance between the surface of the reinforcing steel and the nearest concrete surface.
- Protects rebar from corrosion.
- Ensures fire resistance.
- Crucial for proper bond development.
Memory trick: Cover right, Spacing true, Clean rebar, Secure too.