Encasing DIP in Concrete, Bad Idea?

[sportsnut44]

I've heard mixed opinions about having a cast-in-place concrete encasement around DIP, say for water systems. I've seen it done many times, but I've heard that some people have concern over the concrete being in direct contact with the DIP. What is the concern, and is it valid? Would a possible fix be to put Poly-wrap around the pipe before casting the concrete? Are there concerns regarding the joints, i.e. concrete getting at the rubber gaskets? Maybe another reason to use the poly-wrap before pouring the conrete? Your thoughts are much appreciated.

 

[rconner]

I think this subject has been discussed many times on this and other forums over the years e.g.

http://eng-tips.com/viewthread.cfm?qid=154610

(you could probably get many more perspectives using the "Advanced Search" feature). I suspect more concrete in the past century or more has probably been cast directly against iron than otherwise, and I personally have not heard of problems with pipes or joints as a result of this practice (or for that matter wrapping). If the soils are corrosive adjacent the concrete, it might well make sense to extend the wrap at least a few inches into the encasement. In the process of thrust blocking bolted mechanical joint bends, I suspect some folks wrap the joints and at least bearing side of the fitting, perhaps to keep them reasonably clean of unintentional concrete, or to facilitate more ready bolting/removal if anyone wants to in the future etc. If waterstop function is desired e.g. through a wall, you probably don't want to wrap, at least all the way through a wall! Where pipelines enter and exit concrete encasements or structures/walls etc., some designers like to provide a close flexible joint, or two in the form of a for sure "rocker pipe" where a pipeline exits and/or enters the structure or encasement, to provide for future relative movement of these joining features without unnecessarily stressing the pipeline or the structure.

 

[bimr]

The manufacturers of ductile iron generally state that concrete is not corrosive to ductile iron because concrete has a high pH.

Chlorides from road salt are probably more of a concern for corrosion to ductile iron than concrete.