Extending an Existing Concrete Wall Height

[marinaman]

I've got a client who wants to take an existing site wall, and due to a slight new grade requirement, extend the wall vertically another 6" or so.

The existing wall is 8" thick, about 50' long, and was built 20+ years ago. The top of the existing concrete wall has chamfered edges.

Here are my thoughts to do this:

- If any poor concrete areas are identified, they must be chipped out from the existing wall.
- The top surface of the existing concrete must be roughened.
- Dowels out of the old and into the new must be epoxied into place.
- Some configuration of reinforcing must be determined for the 6" tall by 8" thick continuous extension.
- The existing surface must be prepared with a bonding agent.
- The extension formed

And here's the kicker........what would be poured into the form? Do you guys have any suggestions for such a narrow and thin wall extension?

If typical concrete is used, I'd want low w/c ratio (<0.40), high flowability (slump > 6"...not gotten by adding water but by superplasticer), small aggregate, and admixture added for shrinkage compensation. Should I go this route, or have the GC by a pre-packaged mix of this type? Does a pre-packaged mix of this type even exist?

 

[hokie66]

That is not a narrow extension. 8" wide and 6" thick is quite easy to do. Use normal concrete.

Do your preparation as indicated, except leave out the bonding agent. Most of these require careful timing, otherwise they act as debonding agents. Portland cement is a good adhesive, so you don't need anything else.

Use a couple of bars in the new section, and tie them to your new dowels. But the capping will crack because of restraint of the existing wall, so provide joints at about 10' centres, as well as extending any existing joints to the top.