Cured In Place Pipe Rehab

[gbowen]

I am currently working on a project where we are using a cured in place liner that consists of an unsaturated polyester resin that is used to impregante a tube.

The question I have is that samples taken from the tube in the field and cured in a plate configuration are consistently achieving higher flexural strength results than samples restrained inside of a section of pipe and removed to be tested. The curing is identical, the major difference is that the pipe sample has to be planed to make a flat sample, therefore removing the curvature.

Any ideas?

 

[Demon3]

Strength and modulus both depend heavily on fibre orientation and length. When I imagine the planing process it seems to me that it would cut across the fibres and reduce the mean length of fibre right where they are needed most. So, as you probably suspect the effect you see is probably not real but due to the sample preparation. The other factor is that the planing will expose bare fibres on the surface and these may lead to easy crack formation and premature failure. This would also explain the low values you are seeing.

 

[gbowen]

Demon3

I appreciate the response. We have also seen reduction in strength when we don't plane the sample but leave the curvature. Any thoughts on this? Is there any reason to believe that curing the sample inside of a pipe and then releasing it to prepare for testing would lower the strength?

 

[Demon3]

I don't have any really solid answer. The only speculations I can some up with are:

1. The pipe, if made of metal may alter cure of the resin (some metals decompose peroxides)

2. In the pipe I assume one side is open to air and oxygen inhibits cure. In contrast when cured between two plates the oxygen is better excluded