Waterproofing CIP Box Culvert Joints?

[damorim]

Hey everyone, I'd like to get a feel for typical waterproofing details that are used for construction joints on CIP box culverts. I am wrapping up a design on a twin barrel CIP reinforced concrete box culvert that will be constructed in two stages (i.e. there is a construction joint the full perimeter of the box section splitting the box into two halves). This is being done to stage construction. Additionally, there are the typical construction joints between the floor slab/walls and walls/roof slab. I've seen several details now ranging from nothing, to internal PVC waterstops, to blueskin being applied externally, to a combination. Example, see this one below.

A colleague asked me why even bother placing a waterproofing membrane on the exterior of the joints at all seeing as the culvert is flowing full of water anyways. It got me thinking, what would be the purpose and why have I seen it many times before? One can argue it is to prevent soils from washing in but that would require quite an opening of the joint. Any thoughts on the matter?

 

[damorim]

And to add to that, the Client would like blueskin on the Staged construction joint between culvert halves but would like to forego the blueskin on the typical joints at floor slab/walls and walls/roof slab joints.

 

[MotorCity]

There are two possible scenarios for flow across the construction joint: groundwater seeping in and contaminating the culvert contents (such as treated water) or culvert water seeping out and contaminating the soil (such as sewage or untreated water.)
Structurally, a waterstop can also prevent intrusion of water into the joint and corroding the rebar but you would need 2 waterstops. A bentonite waterstop on each face of the wall would work.

 

[damorim]

Thanks MotorCity, in either of those cases (treated water or sewage water within), that makes sense to me. But, in my case and in the case of the common details I've seen, the culvert is simply under a roadway on a minor river/creek. I agree with the double waterstop if the intent is to protect the rebar. But, most of the ones I've seen either have a PVC waterstop half way through the wall (between reinforcing layers), or only on the exterior side of the wall such as in the detail above. In these cases, whats the point?

 

[MotorCity]

In your case, if you did nothing the only issue I would be concerned with is rebar corrosion. You might want to consider epoxy coated bars. Caveat on my previous statement.....don't place bentonite waterstops too close to the face of the concrete. When they expand, they have the potential to spall the finished face of concrete. If it were me, I would make some attempt to mitigate the issue.

 

[cvg]

There are three possible scenarios for flow across the construction joint - the third is that water flowing through the box sucks soil into the box culvert through an open joint. this will eventually result in voids around the culvert, settlement and potentially sinkholes. So making the joint "soil-tight" is critical. The blueskin should do it. With adequate reinforcing, this is not usually a problem. With pre-cast it is a big problem.

 

[damorim]

Thanks cvg, I think that is probably the intention of the blueskin on the details that I have seen. But as you mention, I feel protecting the joints to be much much more of a concern on precast units. The client wants blueskin on the staged joint, so I'll just go with it.

 

[dik]

I almost never raise the pour joint above the slab or put 'haunches at the top of walls... very costly and additional rebar is cheaper. I know it's an old type of detail common with a lot of municipal work, but, I haven't done this for years.

Often use blueskin for electrical vaults. Another good product is BlueStuf by Penkote...

Dik