Super Flat Floors & Construction Joints
Super Flat Floors & Construction Joints
(OP)
I've got a 250 thick SOG on good soil. It's going to support some serious rack loads and will be travelled by a fancy cherry picker that runs on guided wires saw cut into the slab. Super flat floor requirements apply.
Our original design was rebar and frequent construction joints.
We met with the GC and the specialist slab placing/finishing contractor. The told us that the way to go was to omit the rebar and use BASF steel pins. More importantly, they said that we should pour the slab in a series of strips the full length of the building (200') with no construction joints perpendicular to the strips. This would involve the use of a low shrinkage concrete mix etc.
The specialist slab contractor advised us that control joints fare very poorly when steel pin reinforcement is used. Curling of the concrete at the saw cut joint. They also pointed out that our flatness requirements are not aesthetic, they are for the benefit of these wire guided lifts. Therefore, a random but small crack in the slab may well be less detrimental than a curled control joint.
We went along with all this more or less. We still haven't decided on the construction joints however. On Friday, we spoke with the company that will be providing the testing machine (one of only four in North America apparently) for assessing the flatness of our floor slab in real time. They seem to be quite expert at this super flat slab business. They recommend that substantial rebar be used as well as frequent, well dowelled construction joints. They too seem to be most worried about curling.
So... does anybody have any experience with super flat slabs that they would be willing to share? Control joints? No control joints? Rebar? No rebar? It's getting to be a bit nebulous for my liking.
Our original design was rebar and frequent construction joints.
We met with the GC and the specialist slab placing/finishing contractor. The told us that the way to go was to omit the rebar and use BASF steel pins. More importantly, they said that we should pour the slab in a series of strips the full length of the building (200') with no construction joints perpendicular to the strips. This would involve the use of a low shrinkage concrete mix etc.
The specialist slab contractor advised us that control joints fare very poorly when steel pin reinforcement is used. Curling of the concrete at the saw cut joint. They also pointed out that our flatness requirements are not aesthetic, they are for the benefit of these wire guided lifts. Therefore, a random but small crack in the slab may well be less detrimental than a curled control joint.
We went along with all this more or less. We still haven't decided on the construction joints however. On Friday, we spoke with the company that will be providing the testing machine (one of only four in North America apparently) for assessing the flatness of our floor slab in real time. They seem to be quite expert at this super flat slab business. They recommend that substantial rebar be used as well as frequent, well dowelled construction joints. They too seem to be most worried about curling.
So... does anybody have any experience with super flat slabs that they would be willing to share? Control joints? No control joints? Rebar? No rebar? It's getting to be a bit nebulous for my liking.






RE: Super Flat Floors & Construction Joints
Curling is a huge issue with SOG's and the type of vehicle I believe you have. If I was to use a SOG I would go without joints, using a system called joint free slabs, basically they create lots of small cracks in your slab at small spacing's. I use this system once when no joints were allowed and PT was not allowed. http://www.jointfreeslabs.com/.
As for the first issue, I would put REO in, a small crack is ok, a large crack will get you in huge amounts of trouble.
Arguing with an engineer is like wrestling with a pig in mud. After a while you realize that they like it
RE: Super Flat Floors & Construction Joints
RE: Super Flat Floors & Construction Joints
Arguing with an engineer is like wrestling with a pig in mud. After a while you realize that they like it
RE: Super Flat Floors & Construction Joints
These actions will reduce the curling potential.
Saw cut joints and backfill with semi-rigid epoxy. You can increase joint spacing over standard.
RE: Super Flat Floors & Construction Joints
RE: Super Flat Floors & Construction Joints
Design to a large degree was based on recommendations by the concrete contractor and floor "specialist".
I wish that I could tell you how this project specifically turned out, but the owner backed out and construction did not happen.
RE: Super Flat Floors & Construction Joints
RE: Super Flat Floors & Construction Joints
RE: Super Flat Floors & Construction Joints
For what it's worth, I toured another facility in town with a similar slab and a wire guided lift system. The building is about six years old. The stats are as follows:
Thickness = 6"
Reinforcing = 30 kg/m^3 steel pins only (no rebar)
Control joints = none down the lift isle
Racking = 40' high furniture storage (moderate load)
Mix = low shrinkage mix with relative little cement or fly ash
Placing = non-pumped concrete
The slab looks alright for the most part. Most isles only have one or two spots that required grinding to meet FL65. Cracks tended to be small and spaced at about 15' o/c. As was purported, no curling was evident at these cracks.
There was, however, one large crack that formed with a width of about 2mm. This crack did in fact exhibit some curling.
Does anyone have an explanation for why curling seems to occur at cracked control joints but NOT at randomly formed cracks? That's still something of a mystery to me.
RE: Super Flat Floors & Construction Joints
can I query what you mean by pins, I am getting confused by the kg/m3 because I thought that pins were dowels.
I like Hokies idea of seeing some previous jobs, but I would want to know more than just the stats as you have reported.
I would want to know:
Was the slab poured with or without the roof?
what was the bedding material? (as Ron pointed out the vapor barrier should be under 4" of gravel or similar).
What was the machine used for finishing? (Lazer level ect)
did they lazer level the bedding?
what do they do different from then to now.
as for the crack, I would assume the crack occurred due to thermal movement, thus the curling due to differential shrinkage between the top and bottom of the slab was relived due to the self weight of the slab around. I have linked two PDF's that are worth the read.
http:
http://www.nrmca.org/aboutconcrete/cips/19p.pdf
Arguing with an engineer is like wrestling with a pig in mud. After a while you realize that they like it
RE: Super Flat Floors & Construction Joints
Because while we are discussing the slab, The base is also important. but I'm sure your well aware of this fact.
Arguing with an engineer is like wrestling with a pig in mud. After a while you realize that they like it
RE: Super Flat Floors & Construction Joints
Still pins in my market are steel fibers of sorts. They resemble flattened out paper clips. They're about 50 mm long and have simple deformations at the ends to facilitate anchorage.
Of the extra data that you mentioned regarding the existing slab, all that I know so far is:
1) The finishing machine was lazer level.
2) The big difference between the existing and proposed slabs is that the proposed will shrink more. The original slab concrete was not pumped. The proposed slab concrete will be pumped. As such, it requires a higher cement content (at least according to our supplier).
What is "CBR"? A compaction measure? Thanks for the PDF's. I'll check 'em out tonight. I don't quite get your explanation of the larger crack. Maybe it'll come to me after I read up on it.
RE: Super Flat Floors & Construction Joints
Even i don't understand what I have written half the time :).
CBR is the California bearing ratio, htt
I don't know what you use in the UK (I think your in the uk but most probably your not) to spec the subgrade. Here in Aust we use CBR's and level of compaction.
I don't know much about steel pins, Ron from memory has a large knowledge of this type of reinforcing. Maybe he can shed some light on using these pins in a pump situation, from my knowledge this can be problematic.
Arguing with an engineer is like wrestling with a pig in mud. After a while you realize that they like it
RE: Super Flat Floors & Construction Joints
When you look at the pins, it is quite surprising that they can be pumped at all. They're going to be mixed in at the plant no less.
RE: Super Flat Floors & Construction Joints
Arguing with an engineer is like wrestling with a pig in mud. After a while you realize that they like it
RE: Super Flat Floors & Construction Joints
The use of "pins" in this threads is new to me too. I call them steel fibres. Steel fibre concrete can be pumped, although it can cause problems for the uninitiated.