Exterior Concrete Slab Question

[dmaxfireman]

I have been getting ready to have a concrete slab poured and it should be done in in the next 7-10 days. Slab is going to be exterior in front of my barn in CT.

Slab details are;
18' wide x 33 long
Base was excavated and 18-20yds of process brought in a compacted.
Rebar started out as #4 on 24" centers with #5 perimeter, then a friend dropped off a truckload of free #6 which is now tied inbetween making 12" centers.
Pitch is 0.6% away from the building
Slab thickness will be 7.5" in the middle and 11" at the edges with 4500psi mix
Will be saw cut into 9' x 11' sections


Now the question, I am wondering what I should do for caulk / filler in the joints to keep water from getting in and freezing this winter and causing damage.

 

[papp101]

1/4" backer rod and sikaflex self leveling caulk would do it, you could also just buy a lot more caulk and skip the backer rod. This would be one of those few times you want that battery operated or pneumatic caulk guns. Pro tip- warm your caulk tubes to 80 degrees or so to save your hand, makes it way easier.

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[ConCretin]

Keep in mind that to help ensure that shrinkage cracks occur at your control joints, the recommended depth of cut is 2" in an 8" slab. Since all the rebar actually increases the likelihood of shrinkage cracks, you'll probably want to follow the recommendation.

Your saw cuts won't open up very much, which makes it a little difficult to get a good joint profile with backer rod a sealant that can accommodate movement. On the other hand, your joints won't see a lot of thermal movement so the sealant doesn't have to do much other than fill the gap.

I'm not sure I'd bother doing anything but you could give the slab a few weeks for the joints to open up as much as they are going to and then fill them as best you can with a good polyurethane sealant. If you are really ambitious, you could open up the joints with a crack chaser blade and create a nice joint profile with backer rod and sealant.

 

[dmaxfireman]

Yes the plan was the cut 1.75-2in deep.

I was under the impression that more steel would result in less cracks not more.

 

[scout57]

Pour at the specified slump don’t add any more water
Wet cure for a week
Sounds confusing I know but concrete that’s over watered can never reach its design strength.
And the biggest mistake folks make is not curing properly
Wet cure as long as possible

 

[ConCretin]

Yes the plan was the cut 1.75-2in deep.

I was under the impression that more steel would result in less cracks not more.

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Most cracks result from shrinkage. Since rebar restrains the slab from contracting, it actually increases the likelihood of shrinkage cracks.

Rebar will also keep cracks from opening up and maintain the integrity of the slab including the cracks that form in the bottom of your control joints.

 

[dmaxfireman]

Most cracks result from shrinkage. Since rebar restrains the slab from contracting, it actually increases the likelihood of shrinkage cracks.

Rebar will also keep cracks from opening up and maintain the integrity of the slab including the cracks that form in the bottom of your control joints.

Thank you for the knowledge, will fiber reinforcement help to avoid the cracking or should I be prepared to just live with it if it happens?

Also I fully expect the cracks at the control joints, is this what you're referring to or will these shrinkage cracks be in addition to what will happen below the surface of the control cuts?

 

[ConCretin]

Fiber can help delay and minimize cracking but it won't hold cracks together once they occur. Cracks in a steel reinforced slab are primarily an aesthetic issue and don't necessarily affect its performance. You will have cracks at the bottom of most of your control joints - that's why you cut them - but what you can't see won't hurt you. Avoid the ugly random surface crack with timely and properly spaced control joints and the cracks will be put of sight and out of mind.

 

[dmaxfireman]

Will daytime snow melt that drains into the control cuts and freezes at night be a problem? That was my primary reason for the joint filler. If it is not something I need to worry about then I will leave it alone.

 

[matt_i]

What are you parking on that which requires that extreme thickness? You could run a truck freight terminal with that thickness!

 

[joes169]

First, this is WAY overkill for 99.9% of applications, but that's your choice. Professionally, as someone who's likelihood revolves around concrete, I'd spare the wasted concrete to help prevent the waste of valuable resources.

Second, .6% pitch works on paper, but if you concrete finishers aren't extremely precise, you may need to expect to see some puddling of water. The industry standard on concrete is 2% minimum pitch.

Best of luck.

 

[ConCretin]

Will daytime snow melt that drains into the control cuts and freezes at night be a problem? That was my primary reason for the joint filler. If it is not something I need to worry about then I will leave it alone.

Sealing the joints is undoubtably the correct thing to do but there are millions(?) of feet of control joint up here in the Northeast that are left as is. Wider joints tend to get sealed but control joints rarely are and it doesn't seem to be a problem.

 

[dmaxfireman]

Sealing the joints is undoubtably the correct thing to do but there are millions(?) of feet of control joint up here in the Northeast that are left as is. Wider joints tend to get sealed but control joints rarely are and it doesn't seem to be a problem.

Great, thank you very much for all of the experience and wisdom, I really appreciate it. I will give it a month to contract after the pour and cut and then re-evaluate.