Potential Concrete Crack

[JoeBaseplate]

This is more of an academic question for my knowledge. Please see the attached sketch for a repair to the top of a retaining wall (primarily aesthetic). The two 4x4 haunches on either side are to be saw cut so that the arch can place reveals for aesthetics. I could ask for the whole top to be taken down by 8” and re-install new but for argument’s sake if I go with the attached layout, would there be a concern for cracking at the locations I highlighted? The only load this may see is college kids sitting on it or may be jumping off to the paved surface below.

FYI- Across the length of the wall, we intend to install CJs every 10’ or so for shrinkage control.

 

[a2mfk]

Joe,
I think it'd be easier and much less chance of cracking to remove it in a clean horizontal cut. But for argument's sake, I'd be more concerned with a potential horizontal crack as the top shrinks and the notches resist that shrinkage. But your hooked rebar should take care of that. Although that is not much concrete and such a short width, the shinkage would be minimal in the short direction.

 

[TXStructural]

You can reduce corner cracks by chamfering the top corners of the base , but this will likely be meaningless unless the concrete material used is low shrinkage. If you use a bond-breaker and possibly a voiding material between old and new, you might get good performance of the "cap." Alternatively, bond the two together well and use a high-range water-reducer and low water-cement ratio (unless you use a bagged repair concrete). Also, be sure the base concrete is wet to avoid premature drying along the interface. Damp cure the new material more than you think necessary, and dry it slowly (or as the supplier recommends, for bagged material.)

Your architect might consider a reveal along the side, corresponding with the top of the base material, so any crack will be where planned, like a control joint.

 

[a2mfk]

That's a good idea TX- cut it horizontal and provide a reveal at the cold joint. Easiest and best chance for success. My 2 cents...