Flowable Fill

[Paul Sweet]

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?

 

[classicT]

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.

 

[fatboy]

I would agree with Ty J.

 

[e hilton]

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.

 

[Phil]

See 2018 IBC section 1904.2 for non-structural concrete. The minimum strength depends on exposure, but there is nothing less than 2500 psi.