Concrete Guru's: Your Thoughts Regarding Construction Joint Keyways

[lakeroadster]

My concrete contractor wants to pour the slab for my barn in two pours. I'm all in on the idea as it gives them more time to do a good job without rushing to do the entire slab in one day.

The contractor suggested using a keyway at the slab to slab joint. I've done some research and created the sheet shown below.

Questions:

1. In your experience is a keyway a good option?
2. How long should I request they wait before the first pour and the second pour?

Slab Data:

• 5" thick
• 4,000 PSI Concrete
• Angel Hair Fiber
• 6 x 6-W2.9 x W2.9 Wire Mesh installed on 2" concrete dobies spaced on 24" center to center.

Thanks for your input.

 

[nehog]

The keyways seem smart, however a 30x44 slab is not that large. My 30x60 was a single pour, and they had no problems finishing before nightfall.

 

[Ironcrow]

I have a keyway joint down the center of an 800 sq ft garage. Made with QuicKey galvanized thing that is left in place. The floor is smooth finish, no saw cut or groove. Pad is 5 inches thick. Also dobies, and #4 rebar. I forget the spacing. It has been down for 10 years and you can barely see the seam. So, no issues.

In my area, plastic chairs are rapidly replacing concrete block dobies. Last time I looked for dobies, nobody was carrying them.

 

[tlmartin84]

I split my shop into 4 pours. 3 of which were separated by the galvanized key. I also separated my approach slab. It makes it easy to screed.

It is often called screed key or key lock.

Here are the pictures of my approach.

FWIW, WE PUT KEYS IN EVERY BRIDGE DECK THAT YOU DRIVE ACROSS.

 

[tlmartin84]

View media item 60370
View media item 60371
View media item 60372

 

[lakeroadster]

Thanks Guys.

Tlmartin, thanks for the data and pictures of the screed key. I learned something today

Having the steel in the joint makes a lot of sense as opposed to making the key out of wood and attaching it to a wooden form.

I'll check at the local HD White Cap on price and availability.

http://www.whitecap.com/shop/p/bometals-pro-key-4-1-2-x-10-control-joint-4500

 

[tlmartin84]

One additonal thing I would add is..............

It is flimsy, so be aware of what you are driving the stakes into. I would opt for the longer stakes. On my interior pour I had backfilled with 57's so I actually welded rebar onto the stakes to make them longer and stronger.

I also shoot some self tapping screws through the key into the stakes to make for a more rigid connection. It's a little more work, but it keeps things straight. I also trim one end of the keys so that they overlap and screw them together, think bell fitting on a piece of pipe.

And lastly be aware they make different thicknesses depending on your slab.

 

[Radix2]

My slab is 85x40 plus an additional 27x27 room and another 12x10 room - with 3 different floor heights.

It was poured in one day by 5 guys - it was in the 40s, so they said if it was summer they would have poured the smaller rooms on a different day.

There was no rushing around and there was time after power troweling to hand trowel the 27x27 room to a very fine level as a final finished floor, wait for added concrete trucks, etc.

foam/vapor barrier and pex under all of it. 6 bag mix, floor drains with 4 separate drainage areas, ect. I think it was about 75 yards total.

Final finish is beautiful.

I would seriously consider why these guys need to pour that amount of concrete in two days. I know that if there is no vapor barrier to contain the water, things can harden quick - do you have a vapor barrier or insulation - maybe that is the difference?

 

[MagKarl]

How many yards do trucks in your area carry? You might want to consider tuning the slab thickness to get a total volume that prevents needing a short or extra load.

I don't have a problem with multiple pours but I like continuous rebar. When I did mine I notched or drilled the forms to run rebar through, then pull form and pour the next area. I would worry a keyway will not prevent slabs from moving apart unless you have a plan for your mesh that I didn't catch here.

 

[tlmartin84]

Good catch on the mesh wire, the metal keys have punch outs for the rebar (they are on 3" centers so you can space them as you need. There are no provisions for mesh.

Personally, as you can see from above, I like #4 rebar on a minimum of 24" spacing. Shown above are #3's on 24" but I am not loading anything real heavy on it, and it is nearly 6" thick.

A slab with fiberglass and rebar is pretty near bullet proof. My internal slab is 5.5" x 30'x34'. Divided into 3 -10' slabs by key, and saw cut at 13'3" centers. No cracks nearing the second year.............

 

[dankrism]

I just had a 40x60 garage floor poured in one day. They used rebar and wire so they needed a concrete pumper to get the product in the garage. It is 6in thick on one side where the RV will be parked and 4 in elsewhere. There was no problem in getting it poured and finished. They worked late but the floor is beautiful! The contractor said the QC guys at he plant made up one of the best mixes he had ever seen and I should have even more than the 4000 psi he had promised.

 

[Firebird 1]

No problem with a key way. Its good construction practice. You will need a control joint somewhere it may as well be with that. When we did them we would put rebar dowels to tie the slabs together. We would sleeve the rebar on the side of the keyway that is poured last to allow a bit of movement. We would often place 10,000 sf plus slabs.

 

[lakeroadster]

I would seriously consider why these guys need to pour that amount of concrete in two days.

2 pours... be it 2 days or 2 weeks, it's all good.

It all has to do with resources. How many guys, how many trucks, etc. I respect the contractor that knows his abilities and the constraints of the local mix plant, and stays within those constraints and resources to provide his customer (me) with a consistent quality end product.

I live in a small mountain town. We have a good mix plant, but they are understandably busy with other projects. My contractor knows that, and plans accordingly.

 

[joes169]

If I were pouring it, I'd try to split it right down the middle to limit the amount of mating edge that needs to be finished. Keyway's formed with temp. wood forms have been around for decades, and work well. I've never been a fan of the metal stay-in keys, especially outside. It's inevitable that they're going to corrode and expand at some point. Here's a product we use on a regular basis, simple and effective IMPO:

http://www.greenstreak.com/subpacks/Speed_Dowel_Brochure_featuring_Speed_Load.pdf

 

[Radix2]

2 pours... be it 2 days or 2 weeks, it's all good.

It all has to do with resources. How many guys, how many trucks, etc. I respect the contractor that knows his abilities and the constraints of the local mix plant, and stays within those constraints and resources to provide his customer (me) with a consistent quality end product.

I live in a small mountain town. We have a good mix plant, but they are understandably busy with other projects. My contractor knows that, and plans accordingly.

I hear ya, and that is a good attitude.

But still, here you are looking into now having to make some complex joint and when it comes time for them to finish ( what kind of finish are you planing - broomed, hardtroweled ?) you now have some additional finish work that hey need to get right - hand troweling those edges may not blend well with the power ? troweled middle, hard edges to keep level, troweling mess getting onto the old pour when they come back, etc. It is simply a simpler job to do it all and finish it all at once- seems like a lot to take on just to leave a tiny 7 yard effort for the next day.

what you are doing is not like the example above where the keyway is poured on both sides at the same time and finished together. It is going to take some extra skill to get it to look good and straight.

Contractors and plants can talk and make sure the job is scheduled properly - a 7 yard difference is not going to be the issue.

Are you doing a vapor barrier? expected temps around time of pour ? Is the building over pour?

I know and agree the last thing you want to do is push these guys into doing something they don't want to do, but don't ignore the risk of working with these keyways that they aren't experienced with and I would think have some learning curve, especially using them as a form edge.

IMO if you are going to go with the multi day pour, might as well let them do it their way entirely - however they normally do keys, etc.

Good luck and I hope it looks great !

 

[HemiRamOn22s]

I didnt use keyway in my main pour on my shop but i have it in my shop and basement slab. There is no need for a 5" thick slab with fiber and 6x6 wire mats. Thats just overkill. Your going to want to sawcut the floor from left to right half way back or use zip strip. My concrete crew poured my 40x80 shop and 10x40 side room in one day no problem. Everything was power trowel finished. It was a beautiful 60 degree day. I did use a pump trailer rig and 4,000 lb mix because it pumps better than 3,500 lb mix. They poured my 10x40 covered porch and 3 aprons the following day.

 

[lakeroadster]

The guys showed up to place the forms for the 1st pour on my shop slab. After they left I placed the BoMetal galvanized steel keyways.

I still need to tape up the joints and openings... I wire tied the 10 ft key sections to the forms, so we can simply cut the ties once the forms are ready to be removed.

Thanks for the input, especially tlmartin84 for turning me on to the metal keys.

 

[MagKarl]

Are you going to run rebar through the knock outs in the key strips? Your call, but I would.

 

[lakeroadster]

Are you going to run rebar through the knock outs in the key strips? Your call, but I would.

I am not. I know opinions vary all over the map. Here's how I look at this case:

• The location of the joints, in this instance, is between overhead doors, parallel to vehicle movement. There will be no vehicles driving over these joints.
  
• The sub base was compacted and tested. Average compaction was 97% and all readings taken were within 3%.
  
• The barn support columns trap the slab and prevent slab lateral movement.
  
• 6 gauge 6" x 6" Wire Mesh and Angel Hair Fiber are also being used.

It's been my experience, from an Engineer's perspective, that excessive constraints create high stresses, which lead to material / component failures.

 

[HunterDan]

That job 2 post above mine looks like a nice job.

My contractor talked me into doing a cold key joint splitting my 40x48 slab into 4 squares. The rear of the building was 1 pour and the front was another. Instead of setting the joint they used those half *** metal spikes to try to keep it up

I am EXTREMELY unhappy with the outcome. I asked multiple times if I still needs as cuts, was told no every time. Naturally, it cracked along the joint in both directions and now I have a shittylookkng crack going right through the middle of my garage length ways and side ways.


Just another thing to think about