PVC Communication Conduit Encasement in Concrete

[theCorkster]

We have a project where a set of communication conduits are immediately adjacent to foundation improvement work(compacted aggregate piers).

The design-build contractor proposes to encase the PVC conduit in 3000 psi concrete to protect it from the drilling, filling and compacting operation associated with CAP.

My concern is with the potential for concrete heat of hydration to damage the conduit and cause problems with the interior communication lines.

I've contacted several pvc conduit manufacturers to see what information they may have with respect to what the pipe can accommodate without deformation.

It's not likely that filling the conduit with water will be acceptable to the communications company.

Thanks for any experience or ideas.

 

[1503-44]

Doesn't sound like a problem, but contact the cable owner and let them know. They may want to attend the event to ensure no damage is done, if nothing else.

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[theCorkster]

Thanks - the owner is aware and just does not want disruption to service in their conduit. While I suspect it may not be an issue, I need soemthing to corroborate. I get the impression that they just want me to say go and then we get to see what happens. I've contact several PVC manufacturers and have got zero response so far. I have been able to find that:

"The tensile strength of plastics decreases with increasing temperature. For example, PVC loses about 2% of its tensile strength for each 1°C rise in temperature, rating zero for long term strength at 70°C (158 °F). Tensile modulus likewise decreases, although non-linearly. Plastics pipes do have short-term strength beyond their maximum operational temperatures, but the rate of visco-elastic creep is so high that to all intents and purposes it is not usable"

And I've also discovered that the calculation of the heat of hydration of concrete is sensitive and requires specific inputs on cement type, content, aggregate temperature, confining temperature, structure configuration, etc. - sufficient to say I cannot find a "back of envelope" approach. that gets me any warm fuzzy feeling.

 

[LittleInch]

What sort of encasement?

You've got to get metres worth of concrete before the heat gets to be an issue - think Hoover dam levels

This is a non issue/ prove a negative.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[1503-44]

Get a couple of bags of cement and some PVC pipe and try to damage it yourself.
I have never thermally burned my hand touching curing concrete. Heat is a problem for concrete hardening too rapidly, insufficient hydration water, rapid expansion, shrinkage on cooling, cracking the concrete itself and its remaining strength. Nothing should affect the PVC at all.


--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[theCorkster]

Thanks for the comments and ideas. I did have a colleague with experience with the heat of hydration issue confirm that the concrete set temperature should not be sufficient to damage electrical conduit PVC. I did obtain some data on current plastic pipe requirements and they typically are not of concerned with temperatures under 70 degrees C. He also raised the question as to why I was responding to this as it did not seem to be in the realm of geotechnical engineering - and I think he is correct. After reflecting on the issue it seems more like trying to expand the liability pool in the event there is damage to the conduit and/or disruption of communications. I see that providing input to a decision that the contractor is supposed to make (means and methods) does create liability. Typical specification language requires the contractor to protect utilities from their operations. And that is the approach I'm going to go with.

 

[1503-44]

Smart move. In any case, don't worry about this issue.

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."