Support for duct bank encased in mat foundation

[humanengr]

I am designing a pile supported mat foundation that must encase an existing duct bank.
The thickness of the mat above the duct bank is not sufficient. Otherwise, I would have ignored the thickness below the duct.
So, I must rely on the thickness of the mat below the duct.
Since the duct bank is existing, I'm planning to support it temporarily with re-bar (or steel) frame, as the soil is excavated below the duct bank.
If I let those frames rest on the soil, there will be no cover leading to possible corrosion of the frames and possibly wider area corrosion.
Therefore, I'm planning to raise the frames on small conc. blocks (+/- 6" x 6" x 6").
Here's t he question:
Are there products made that could be used in lieu of those conc. blocks to avoid having to form and pour a few dozen of those blocks?
I'm assuming by making the blocks with roughened surfaces, they will essentially become integral to the mat and there should not be any
infiltration into the mat that could cause rebar corrosion or concrete degradation. Is that a reasonable assumption?
Thank you.

 

[humanengr]

Here's a sketch for the post described above:

 

[SlideRuleEra]

I'm assuming by making the blocks with roughened surfaces, they will essentially become integral to the mat and there should not be any infiltration into the mat that could cause rebar corrosion or concrete degradation. Is that a reasonable assumption?

Not a good assumption. There may be aggregate interlock, but it remains a cold joint.

Can the duct bank be replaced either permanently using a route that avoids the mat or temporarily until conduit embedded in the mat can be put to use?

The entire proposed concept (encasing an existing duct bank in a structural mat) is very poor practice.

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