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Flowable Fill

Paul Sweet

Sawhorse
Joined
Oct 17, 2009
Messages
2,478
Location
Bedford, VA
NEC table 300.5 note 5 allows PVC conduit to be installed at a lesser depth when covered by at least 2” of concrete when rock is encountered. Is flowable fill (low strength concrete – 200 PSI or so) considered concrete for this purpose, or does it need to be regular (3000 PSI) concrete?
 
I'd say that it needs to be traditional concrete. Concrete provides a formidable barrier from excavation.

Flowable fill can be excavated through by a shovel, thus does not provide any protection of the conduit.
 
I agree. If the installer wants to use something that flows easily, they could use a high strength grout, like the kind used to fill in under light pole bases and heavy machinery in equipment rooms. It flows very easily, and gets up around 5,000 psi.
 
See 2018 IBC section 1904.2 for non-structural concrete. The minimum strength depends on exposure, but there is nothing less than 2500 psi.
 
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