I agree with thinfool, if I was excavating above a concrete encased ductbank, I would prefer foil line tape that can be detected, as opposed to red colored concrete that you have to physically come in to contact with in order to locate.The 'red' is in the mind and spec book of an engineer. Nasty, expensive and now that we can install foil backed marking tape above a concrete duct bank, unnecessary.
Don, I was referring to concrete encased conduit, if rmc is encased in concrete, it would be hard to detect with any type of metal detector. Even if it(rmc)is not encased in concrete, foil lined tape placed above the conduit and twelve inches below grade and a metal detector should help to locate your trench.Why would foil backed marking tape be needed for galvanized rigid metal conduit?
Don