undercut/over excavated footing w/flow-able fill

[boffintech]

Got a 10'x10' spread footing that needed to be undercut, over excavated in depth, to get down to suitable bearing material (rock).

Used 19yds3 of 4500psi concrete as backfill to get back up to bottom of ftg elevation.

The contractor wants to place the forms, the rebar, the column dowels, and then place the concrete for this foundation later today even though the flow-able fill was placed this morning. To speed up the flow-able fill set time a couple of bags of calcium chloride were used. No rebar was placed in the flow-able fill so no worries there...and this won't affect the rebar in the footing? Right?

 

[BAretired]

I doubt that there is enough calcium chloride to affect the reinforcement in the footing, but to be safe you could put a layer of 6 mil polythene between the two pours.

BA

 

[doka1]

i like the thought BA, very practical. Not letting them pour the concrete would be impractical, once the get their initial set, enough to place their forms, where is their reason for concern. why 4500??????????

 

[boffintech]

Reason for concern: just curious if that salt can migrate.

Too late for plastic; already poured. The EOR wanted and got a 2'x2'x6"D key in the middle and a rough surface overall.

Why 4500 psi: there is one approved concrete mix for the project so they just used that.

Thanks.

 

[BAretired]

Salt can migrate by capillary action in the presence of moisture, but unless the contractor used more than 1% by weight of cement, I don't think the reinforcement will be adversely affected.

BA

 

[TXStructural]

Assuming that the footing is under a building, the moisture available to facilitate migration of the chloride ion will probably be minimal over the life of the building.

The contractor probably used 3 inch cover for a footing cast against earth, which will provide substantial protection to the rebar.

Except for ease in correctly placing the rebar, I'm not sure why you would need to place the concrete in two lifts, rather than simply locating the rebar in the top of a deeper footing.