concrete cover for liquid-containing facilities 1

[FRACH23]

I have a recent discussion with a consultant about minimum concrete cover for walls for a waste water containing tank. I read in ACI350 it could be only 2", but our Consultant insisted to use 3". We wish to keep my 2" as the code prescribed. I have also some minor low walls inside which is only 10", and taking this large cover for a double curtain reinforcement would place my rebars oddly close.

Any possible basis for the 3"? I just felt its quite too much? I was just thinking a possible reason is for more safery against deterioration. Any thoughts?

 

[JedClampett]

Two inches always works for me. But if the people paying you want 3 inches, well, that's their decision. If you have 10 inch walls, they're too thin anyway. You can't reinforce them, get in waterstop, and get a stinger in the space. I see 14 inch walls in your future.
Note that the Z factors, predicting cracking, change when the cover is different than 2 inches.

 

[FRACH23]

Thanks a lot for this Jed. I may need to economize some minor walls. They are just interior walls only around 5 ft. Interior wall ( not necessary to put waterstop) and not highly stressed, w/c i could still detail to ensure cracking is controlled. But i'll take note on the the "stinger" item, its a good point.

 

[BridgeSmith]

For a 10" wall, presumably with load only on one side, can't you just use one layer of reinforcing on the outside face?

 

[JedClampett]

Trying to get a contractor to place one layer of reinforcing anywhere but the middle is a challenge. If they do skew it, it's just as likely to be on the wrong side as the right side.

 

[BridgeSmith]

JedClampett, to my knowledge, we've never had an issue with getting a single layer of reinforcement in the correct face of a wall for the culverts, retaining walls, etc. that we do. Of course, we have field engineers on-site for QA. I guess it depends on the contractors you're dealing with and the level of oversight provided.