Thermal Cracking of Concrete

[kerrboy1987]

I am designing a concrete retaining wall to Eurocode 2. I have a minimum allowed crack size of 0.2mm. The wall is to be cast against a secant pile wall. We have set a minimum thickness of 500mm and we have specified a nominal cover of 50 mm for the exterior face. In reality though the wall cover will vary as the secant wall profile undulates.

Do I need to take a more conservative approach with reference to the cover or is this approach OK?
Do people know of a better way to detail liner walls against secant walls? Is it better to pour some concrete to get a fair flat finish and then pour another independent section of the secant wall and detail it seperately with more confidence in the cover we can specify.

Thanks for any advice.

 

[dik]

What is the environment and is 50 cover the minimum? What is the strength and do you use fly-ash? 500 thick is not quite what would be considered mass concrete and you may want to drape insulated tarps over the exposed face to minimise any thermal differential... shouldn't be too much though?

Dik

 

[kerrboy1987]

Thanks for the response Dik.

The final Ash content is still to be confirmed. I am concerned about the cracking on the external face of the liner wall, adjacent to the Secant Wall. The issue is with this face the concrete cover can't be fully controlled as the secant wall isn't a flat face so the cover will vary as it goes along the wall.

As the cover has a significant effect on the crack width calculations I was seeing if people had experience of casting a liner wall against a secant wall that was designed to stop water seepage. Should this be a concern?

Thanks.

 

[dik]

Can you use a bentonite 'mat' between... stops nearly all moisture...

Dik

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[hokie66]

I assume you mean a maximum crack size of 0.2 mm (not minimum). As the restraint to cracking is along the full length of wall rather than at discrete points, this actually helps in distributing the cracks, so applying the crack control provisions of your code should do the job. I would base the calculation for required reinforcement on the minimum thickness of the wall, not the maximum.