Joints in Retaining Walls, again... 1

[sybie99]

Good day all,

We are building a retaining wall along the sea front so the wall will be continously exposed to sea water spray, its in a very windy area and thus very aggressive environment for concrete.

The wall is total about 300m long. I am thinking of placing joints at 6m centres. My questions are:

1. Should I have rebar running through the joint so that, in time there is no differential movement between wall sections?
2. If so, is this not a bad detail in such a corrosive environment, of course there will be a joint sealant which should ensure no moisture gets to the rebar, but there is no guarentee the sealnt will be maintained in yeras to come.
3. Should rebar have to run accross joints, should these then be stainless steel dowels?
4. What about no joints, controlling cracking by placement of a large amount of horizontal distribution steel, is this an option?


Thanks for your opinions and advice

 

[JedClampett]

I'd place construction joints at about 24 to 25 ft. These joints have full horizontal steel crossing the joint. They should be given 7 to 14 days between pours of adjacent sections. I wouldn't put an expansion joint (I think you're describing those) in unless they're at about 100 ft. or even more.
As far as differential movement on either side of the joint, you can get different opinions on that. Some engineers like to place in smooth dowels (stainless if necessary), embedded in one side and in a sleeve on the other. I prefer nothing. If you're getting forces enough to move the walls differently, the dowels are not effective. Retaining walls are designed deflect uniformly and I would trust that.
As far as sealants, some are very good, but by their nature you're only going to get 20 years out of them. Maintenance is vital.

 

[dik]

Australia? what is your climate? 1000' is too long without a joint... 30' sounds like a reasonable number. How high?

Make sure you have lots of cover to main reinforcing... 2-1/2" to 3" is not too much... For permanence, can you use HDG rebar?.. I don't like epoxy bars...

Stainless steel dowels sounds like a plan; make sure you pick the right SS...

I've not done much in marine environments... maybe someone else can fill in the blanks...

Dik

 

[sybie99]

Wall height varies from 2 - 6metres. Jed, are you saying one should maybe pour alternate sections so that one can wait 7-14 days before the "infill" wall panels are cast? Does one then place a timber section on the shutter face to create a recess for joint sealant?

 

[JedClampett]

As far as the construction joints (the ones at 25 ft.), we ask for a 1/4 inch chamfer at the exterior of each pour and put in a small bead of caulk. Use a high quality 2 part polyurethane sealant. The chamfer is formed with a a triangular piece of timber or a manufacturered item. These joints have no gap. The contractor needs to have forms that allow the bars to project through. For the expansion joints, they're bulkheaded off.

 

[charliealphabravo]

For expansion joints I would prefer keyed joints to dowels if you must enforce deflection compatibility.

 

[ron9876]

I would use joints at a spacing which is about the same as the height. Unless there is some problem with the face of the walls having a slight offset I wouldn't put anything across the joints. I would stop all steel 2"-3" from the joint and I would form V joints on both faces to control location of cracks in joints. Lots of cover and some of that chemical magic that helps stop water penetration. All steel hot dip galvanized.

 

[hokie66]

What ron9876 said...for a seashore retaining wall. You don't want steel running through those joints.