Dowel between new and existing

[JoeBaseplate]

If there is a new vertical concrete pour against existing, I have seen dowels detailed in a way where they are dipped in grease on the new pour. Is there a better alternative to using grease? Could wrapping in building paper be a more reliable method.

 

[DWHA]

I have seen grease, oil and plastic sleeves. I think that you would like the plastic sleeves.

 

[JoeBaseplate]

Thanks DWHA, I have never shown plastic sleeves on my drawings. Sounds like a better alternate to grease.

 

[JAE]

Joe,
Check these sites out:

http://www.connollykeyjoint.com/universaldowelsleeves.htm

http://www.chemstop.com/SubPacks/Speed_Dowel_Brochure.pdf

http://www.chinoproducts.com/concrete-joint-application.php

 

[JoeBaseplate]

JAE, would you use this in horz (slab on grade) as well as vertical applications?

 

[rowingengineer]

I normally wouldn't provide an expansion joint for vertical extensions. I would need to know more detail to make the judgement however.

How could you do anything so vicious? It was easy my dear, don't forget I spent two years as a building contractor. - Priscilla Presley & Ricardo Montalban

 

[JoeBaseplate]

RE, my question about the vertical use was in regards to a renovation job. A concrete balcony curb (about 14' long, 5" thick, 42" high) is in bad shape and needs to be demoed and replaced. Similar curbs next to it are fine, I am planning to drill into existing and grease/plastic the new ends.

 

[rowingengineer]

I don't think I would provide greased or similar dowels. I would add an extra bit of steel in the kerb and epoxy dowel providing full laps.

How could you do anything so vicious? It was easy my dear, don't forget I spent two years as a building contractor. - Priscilla Presley & Ricardo Montalban

 

[TXStructural]

Unless you want the new work to be free-floating, do not debond the dowels. If you need to debond the ends but maintain alignment, then wrapped or sleeved is common. Greased works until it doesn't, due to corrosion or too thin a layer/getting rubbed off during concrete placement. Also, make sure the dowels are exactly parallel to the vector of movement you intend to allow and are parallel to each other, otherwise they will bind and restrain the concrete.

In your 42" tall knee wall, you will need to prevent rotation at the base unless it is otherwise restrained. The most common way of doing this is to drill into the supporting structure, and install deformed rebar dowels using adhesive. Carry the dowels either one development length, or in your case, the full height of the wall.

I don't see a place for debonded dowels at the base unless the wall is purely decorative and supported by other structure.

 

[JoeBaseplate]

TX, the original curb (handrail if you will) is doweled into the slab below (have existing drawings from 1950). I am going to try to preserve the existing vertical bars but also putting in additional vert bars, doweled and epoxied into slab to have the curb cantilever. The reason I want to keep the two separate is because the existing concrete panels, even though cast in place, appear to have sealant/backer rod in between. See attached.

 

[JoeBaseplate]

FYI-In the pic I posted, the panel on the left has a full length crack across the middle and is sagging an 1" more then the other panels. This is the panel I am demoing.

 

[TXStructural]

Sorry, I probably misread the OP "vertical pour" as "vertical bar".
Yes, preventing the old and new walls from being connected is a good detail. Sleeve the bars if you feel the need to provide a connection. It is not necessary and could place unwanted and unnecessary stress on the existing. Also keep in mind that when the old wall is removed and replaced, there could be rotation, making the new wall pull outward on the existing. Are you certain this is not an upturned beam reducing deflection across the span? (Just making sure you have considered it, since you mention deflection issues.)

 

[JoeBaseplate]

hmm, upturned beam!!! Never thought about that. I don't think it is, because the curb is detailed with minimal horiz bars but let me go and check again. Thanks for pointing that out.

I'll be back....