Wooden pole embedded in concrete vs soil - rot issues 2

[Kom3]

Hello all,

I am wondering which is worst for a wooden pole in terms of rot, embedding it in concrete or soil. The client wants to encase to the wooden pole in concrete so we can increase its diameter in the ground and reduce the required embedment but I feel like encasing it in concrete will be worse for it in terms of rot. My reasoning is that concrete cracks and traps water which will make the rotting faster but I am not sure there is any literature to back that up and make an argument for it. Please note that I will be using pressure treated wood regardless. Any input will be appreciated.

Regards

 

[phamENG]

Dig the hole. Pour in gravel or something capable of draining. Paint the embedded part of the post with a bituminous coating (they sell it specially for fence posts) and set it in the hole - brace as required. Pour concrete, sloping the top surface away from the post. Done. Now you've increased the diameter, maintained a drainage path for moisture trapped in the post, and inhibited moisture from penetrating the sides of the post through cracks in the concrete.

 

[marc.rogue]

I don't think you will find anything other than common sense for this issue. I think if you do a good enough job with your concrete you can limit cracks and how much water will sip in. worse case just paint the embedded side with some hydrophobic type paint and call it a day.

 

[azcats]

Could you use a flowable fill material that is permeable? Wouldn't quite be concrete but would be strong enough to act like soil improvement around the post and transfer compressive loads to the surrounding soil.

 

[Canuck65]

I have recent direct experience that would suggest that the portion of the wood post encased in concrete will significantly outlast the portion of the wood post in contact with soil.

 

[dauwerda]

Make sure the post is properly pressure treated for ground contact (UC-4B) and it shouldn't be an issue with either solution.
Here is a study done on the long-term durability of pressure treated wood:

https://www.fpl.fs.fed.us/documnts/pdf2013/fpl_2013_lebow001.pdf

 

[NorthCivil]

Canuck65

I think the climate and environment this application is in will have a huge effect on how fast the pole rots. They build houses with treated timber foundations in saskatchewan, but not in BC

I am with phameng on this except for the bituminous paint to the base of the post. this paint will trap the moisture inside the post. paint it with latex, or leave it.

 

[Kom3]

Thanks for all the responses. To add a little more detail, these are utility poles designed for the outdoors so they are already specified to be pressure treated. Even if I add gravel to the bottom and pour concrete afterwards, does that ensure a drainage path? If the concrete crack does not reach the bottom where the drainage is, wouldn't the cracks trap the water? I have not seen a utility pole that carries transmission wires embedded in concrete before so I am curious if there is a reason none has done it before.

Regards.

 

[dauwerda]

My experience for direct embed utility poles is that they can be, and are, backfilled with concrete. This is typically not the first option simply because it costs a lot more than using other fill materials (native soils or structural fills). For poor soils where a larger cross section is wanted/needed to resist the ground line moment as you describe I have also seen a culvert installed in the hole with the pole installed inside the culvert. The pole is backfilled with gravel and the culvert is backfilled with native soils.

 

[BridgeSmith]

Even if I add gravel to the bottom and pour concrete afterwards, does that ensure a drainage path?

Nothing fully ensures a drainage path, but if the bottom of the pole is in, or at least on, the gravel, water that makes its way in between the pole and the concrete will at least not be trapped in a concrete 'pit', but should be able to drain into the gravel.

Rod Smith, P.E., The artist formerly known as HotRod10

 

[NorthCivil]

Water always finds a way in. So design considering the 4 D's. Deflection, drainage, drying, Durability.

Deflection: keep as much of the water out as you can.
Drainage: allow a path for water that finds its way in, to weep out.
Drying: don't suffocate and trap water that finds its way to where you dont want it.
Durability: materials should be durable enough to last when things dont go as planned.

keep in mind all of the above will take a back seat to our #1 requirement: economy.

of course some concessions will be made when jamming a wooden pole in the earth as a "permanent" solution.