×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Concrete slab control joints

Concrete slab control joints

Concrete slab control joints

(OP)
I am working on an elevated concrete tunnel, for which the floor must meet "superflat" requirements.  The tunnel width is 20' and is 250' long. The floor is a cast in place concrete, one-way slab with reinforcing in two mats (each direction) top and bottom.  Is it at all realistic to try to cast this slab without control joints?           

RE: Concrete slab control joints

If you don't care about cracks, yes.  If you care about cracks, no.

RE: Concrete slab control joints

I'm confused, oneway slab on ground, what do you mean?

Arguing with an engineer is like wrestling with a pig in mud. After a while you realize that them like it

RE: Concrete slab control joints

Yep, confused.  He didn't mention "ground".

RE: Concrete slab control joints

I picture it as being supported on each side by beams or walls the entire length, making it a 1-way slab.  

Can't quite picture what "(each direction)" means, unless it just means there are two mats with reinforcing steel equally spaced in each direction.  Regardless, it will crack, and the crack spacing will depend on the depth of the slab, the mix design and exposure conditions.

Greg

RE: Concrete slab control joints

Why superflat for a tunnel floor? The added cost will likely be $1 to $2 per square foot for this finish.

Dik

RE: Concrete slab control joints

I must have still been asleep.  

Arguing with an engineer is like wrestling with a pig in mud. After a while you realize that them like it

RE: Concrete slab control joints

The crack spacing and width will also depend on the amount and size of the bars.

RE: Concrete slab control joints

250 ft is way too far to not have joints, no matter how much reinforcing you throw at it.  You might want to re-assess your requirements.

What sort of environment is the tunnel in? Subject to thermal movement? You will have to break it down into a minimum of half a dozen sections and throw in a pile of rebar to minimise crack widths. If a true 'super flat' floor is required, you will have to take extraordinary care at the joints.

Dik

RE: Concrete slab control joints

(OP)
Apparently the original post was not quite clear enough.  It is an elevated concerete slab supported on CMU/CIP concrete walls.  Reinforcing is top and bottom in each direction.  

As Dik mentions I was hoping to use a lot of extra reinforcing to minimize/eliminate control joints, but figured that this distance would be too far to go.  Hariline cracks would not be an issue.  The tunnel is unheated/outdoors and will be subject to thermal movements to make matters worse.   

Thanks all, particulary Ron, very insightful....

RE: Concrete slab control joints

So the problem is more complex... it appears to be a structural slab and you are trying to accommodate elastic and long term deflections and achieve a superflat floor...  Many flatness standards require flatness measurement to be made within the first couple of days...

Good Luck!

Dik

RE: Concrete slab control joints

Maybe you can contact someone who represents a manufacturer of Type K cement.  The slight expansion of the concrete might eliminate the need for standard control joints, but for thermal you're on your own.  I've never used the stuff myself, but it seems interesting.
These guys are always looking for good example projects, so I'll bet they'll be helpful.

RE: Concrete slab control joints

What about using a topping slab?  You could cast the suspended slab and then put down a waterproofing membrane to prevent cracks translating through.  Then pour a topping slab on top and put sawcuts in the topping slab.  You would have more control with the topping slab.  

If the slab was subject to heavy traffic, this may not work though.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources