New Concrete Pedestal to Existing Concrete Interface

[humanengr]

An existing concrete foundation will be surface prepped to placement of a new concrete pedestal.
The concrete pedestal will support rotating equipment. Epoxy grout will be utilized at the top of the pedestal to
support the equipment.
The surface of the existing concrete foundation will be roughened (aggregate exposed), cleaned, and saturated with clean water prior
to placement of the new concrete pedestal. Post-installed rebar dowels will extend into the existing concrete and will be embedded
in the concrete pedestal.
At the concrete interface surface, I typically do not specify the use of a bonding agent.
Question: Has anyone had experience of this type specifically for supporting rotating equipment? I would like to avoid using an epoxy
bonding agent due to potential drawbacks primarily due to working time and the potential for the bonding agent to set
before the concrete pedestal is fully placed.

 

[AskTooMuch]

Yes we've done this on pump and compressor foundation. No need for bonding agent as long as you surface prep correctly including saturated surface dry (SSD) condition.

 

[Klitor]

+1
If its a short pedestal, steel skid placed directly on existing concrete could be a simpler solution.

 

[milkshakelake]

Yeah, you don't need a bonding agent. The rebar dowels will be in tension, therefore not needing the concrete to be bonded. The roughening you specified will provide the shear friction. Compression will be taken by the concrete-concrete interface. If you need more shear resistance, adding more dowels will do the same thing as a bonding agent. I recommend roughening the concrete to at least 1/4" amplitude.

If this were a totally new footing plus pier, I doubt you'd be using a bonding agent. It would be two separate pours, much in the same procedure as you've currently specified but without the roughening, cleaning, and wetting.