Intermittently exposed rebar

[mijowe]

Is there any provision in ACI that allows rebar to be exposed, or to have reduced cover for small portions along its length? For instance if I wanted to trench the top of a slab 1/2" deep x 2" wide, perpendicular to the top rebar to install some electrical lines? I would actually prefer a reference that specifically says you cannot do it.

 

[STrctPono]

Think about this.... when you need to make structural repairs to deteriorating concrete, you have to remove the concrete over the rebar.

There are 2 levels of concrete removal. One where you remove only the clear cover (No more than 50% around the diameter of the bar. Essentially, you leave half the bar bonded to the concrete. I don't take much reservation with these types of conditions and sometimes impose very little restrictions on the Contractor in terms of how large of an area they can remove. I might limit the live load during this time but that's about it. The second is where you remove all the material around the reinforcing steel. You normally need to pay a bit closer attention to this situation to make sure that this isn't in a high stress location... say at the bottom midspan of the beam. Even then, I've done it, but not normally large removal areas. I rationalize it sort of like unbonded PT. For these conditions, we typically limit or eliminate Live Load altogether.

If you are trenching 1/2" deep x 2" wide, and it's running transverse to the main top reinforcing.... that doesn't sound like something that I would be concerned with at all. How are you going to fit an electrical conduit in a 1/2" deep trench? You wouldn't even be exposing your steel with that shallow of a removal.

 

[Agent666]

Minimum cover isn't an optional thing in terms of durability, that is why tolerances on cover are -0 + some dimension.

You can of course get products that reinstate 'x' mm or inches of equivalent cover.

However you also need to consider the impact of cover removal in terms of member capacity, removing 1" of cover in a 4" deep slab for example would need careful thought about the structural implications, removing 1" concrete from an 18" thick slab might be more tolerable.

 

[mijowe]

I agree with the above, but I am also concerned with the fire rating, or at least the protection the cover gives the reinforcement. I was hoping to find commentary that would quantify the amount of allowed compromised cover, or something that I could point to that allowed none at all.

 

[r13]

This is not to say no, but from an experience point of view, the difficulty in making the new repair concrete/agent to have the same property as the original, and bond the two materials together without separation, discourages such practice, except, my opine, absolute necessity.

I've noticed many repair works that cracked again, the failure most likely started with the original concrete been weaker the repair material, and expended in a different rate. Also, if the electric line is a live line, even with steel casing/conduit, is the slab a good place for it from the electrical code point of view?