BONDING EXISITNG CONCRETE TO NEW CONCRETE

[PT999]

I have a project where concrete was placed over a month ago, and now the next pour is scheduled at this joint. Should I be asking for a bonding product at the joint. When would you require this.

 

[KootK]

We could use more info here. Vertical or horizontal joint? What kind of element (beam, slab, etc.)?

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[PT999]

The detail is for a 2 ft x 2 ft concrete pile cap (already placed) supporting 8" thick concrete slab. Pile caps are on an 8 ft grid to support the slab.

 

[KootK]

Do you need the slab and cap to be composite for flexure or punching shear?

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[PT999]

Composite for flexure

 

[KootK]

If it's truly composite for flexural purposes, then you do need to achieve positive bond to transfer horizontal shear forces. In a situation such as this, I would expect demand to be pretty high and I would have rebar dowels installed to get the job done.

Frankly, I'm surprised that you need the composite action for two reasons:

1) I wouldn't think that a relatively small, 2' square cap would contribute much to slab flexural resistance and;
2) It's quite common to have a delay between pile cap pours and suspended slab pours.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[hokie66]

A 2' x 2' block of concrete is going to do little for you as "composite for flexure". The slab should have been designed based on the size of the pile cap, just as for a column support, but trying to bond the concrete by unusual means will do nothing for you. Just cast the slab on a clean surface.