Slab-on-grade maximum pour size
Slab-on-grade maximum pour size
(OP)
Two questions:
1) Is the ACI recommendation for slab-on-grade pour size 9000 SF? If so, in which ACI document is this?
2) Is there a maximum recommended length of pour?
1) Is the ACI recommendation for slab-on-grade pour size 9000 SF? If so, in which ACI document is this?
2) Is there a maximum recommended length of pour?






RE: Slab-on-grade maximum pour size
RE: Slab-on-grade maximum pour size
If the pours are too long, then the construction joints between pours may open excessivly, when the concrete dries and shrinks; the sawcut control joints don't necessarily break open and accommodate the shrinkage movement, particularly if placed on a low friction surface (we have had this problem many yeras ago), so I think it is prudent to have a maximum length of pour.
I had thought that one of the ACI Standards had a suggestd limit in maximum area...I expect it would be the Standard on construction...I should also check books on slab-on-grade.
RE: Slab-on-grade maximum pour size
RE: Slab-on-grade maximum pour size
You seem to be talking apples and oranges here. Ron is talking capacity and you seem to be talking control joint spacing or design.
The 9000 square foot figure would be more related to capacity, but, as Ron says, that is very arbitrary and not in any code document I know of.
However, relating to construction joint spacing, areas of 400 to 900 square feet have been regularly used to control crack width from shrinkage.
Mike McCann
MMC Engineering
RE: Slab-on-grade maximum pour size
I am not concerned with how much a construction crew can place in a day or how many crews may be needed. I am also not asking about control joint spacing (for that we conform to the 4.5 m maximum spacing and not to exceed a certain multiple of the slab thickness depending on exposure conditions i.e inside heated building envelope or not; low shrinkage mix, etc.).
My question might perhaps be most clearly put as follows:
What is the maxium length of pour between construction joints that can safely be used (when sawcut control joints are made at the appropraite timing and spacing in accordanc with good practice) without causing performance issues with the slab? I generally take about 20 m, although this may depend on whether low shrinkage concrete mix is used (a relatively expensive thing to do) but I would be interested in hearing your views. One of my concerns is that the construction joints will open excessively due to shrinkage, if the distance between them is too great, irrespective of how well the sawcut control joints are done.
RE: Slab-on-grade maximum pour size
RE: Slab-on-grade maximum pour size
Maybe I am nissing something here.
RE: Slab-on-grade maximum pour size
RE: Slab-on-grade maximum pour size
It seems from the responses that the general feeling is that our experience is not typical of slab placed on the usual subgrade, even if there is a polyethylene sheet below. That is interesting and I will attribute our experience to the particularities of that job.
However, it leaves me wondering why ACI 223 limits the area of a pour. Why do you suppose that this would be?
RE: Slab-on-grade maximum pour size
RE: Slab-on-grade maximum pour size
RE: Slab-on-grade maximum pour size
RE: Slab-on-grade maximum pour size
RE: Slab-on-grade maximum pour size
RE: Slab-on-grade maximum pour size
RE: Slab-on-grade maximum pour size
RE: Slab-on-grade maximum pour size
Have you found that is the North American Practice in your experience?
I have not seen that specified or done around here but perhaps I am wrong because it has been about 30 or 40 years since I was on site while a slab on grade with mesh was being placed, but I will check with my colleagues when I get into the office. Maybe others on this forum can comment. Like I said earlier, we and many other firms generally stopped specifying mesh in slab on grade about 30 or 40 years ago.
Have you gone to the site to check that it is done?
What do you mean by "large mesh"? For the usual 6"x6" 6/6 mesh, it usually ends up on the bottom of the slab, as many articles have noted and as we have proven by cores. That is why they developed the much wider spaced mesh that the workers can theoretically step between the wires, but which I have not seen used in this area of the continent (Toronto area).
RE: Slab-on-grade maximum pour size
Now i have not done an entire slab on foam so i cannot comment on increasing the saw cut depth but that would be my first thought as well.
RE: Slab-on-grade maximum pour size
Think about the different problems the OP is combining as well: He has mentioned both expansion/contrsction (temperature movement) and settlement: the difference between say a 6 kilometer long uniform road expanding/contracting in the 6 km direction but bending easily as the earth moves up and down under each 5 meter length, and a uniform 45 m x 45 m slab inside a large temperature controlled building on top of a "slippery" insulation.
In the first case, the cut cracks will occur across the road at each 5 cut even if the mesh or rebar isn't cut at the 5 meter joints: There is a lot of resistance between concrete and ground, and the mesh is going to be "flexible" the long way. So the concrete cuts (or joints) at 5 meters are going to work: each 5 meter section will probably not break within the 5 meter, and each section will move independently of its neighbor. Even more so if each lane is separated from adjacent lanes also.
But the big building slab on a well-compacted dirt/fill/prepped area has little reason to "break" at the small 4.5 meter distances, and a lot of reason to behave like was mentioned: the concrete stays together as it contracts (slides over the slippery insulation underneath). So, in the big building, you need to cut much, much more rebar (all of it ?) at each joint to prevent all of the little squares from moving sideways at the same time as the concrete contracts/expands.
Could you put in deeper keyways into the insulation so all of the joints don't have to have cut rebar to support rolling lods like forklifts or trucks? I don't that would work - the keys would be stress risers instead. Pour a fancy (more expensive!) (much slower!) overlapping joint?
RE: Slab-on-grade maximum pour size
http://www.danley.com.au/Product_Joints_Plate_Dowe...
We always use WWF (aka mesh or fabric) with min of 8mm dia deformed wires at 200mm c/c, chaired up on correctly sized plastic supports chairs so it stays in the top of slab - way different to the US practice of "chicken mesh" in SOG.
The only SOG's that I have seen without reinforcement (other than engineered unreinforced pavements of significant thickness) are council/city footpaths, and driveway crossings to dwellings.
RE: Slab-on-grade maximum pour size
RE: Slab-on-grade maximum pour size
RE: Slab-on-grade maximum pour size
60 feet?
75 feet?
100 feet?
150 feet?
200 feet?
no limit?
RE: Slab-on-grade maximum pour size
RE: Slab-on-grade maximum pour size
There are literally thousands of miles of interstate highways and freeways as well airport runways and taxiways, all constructed of jointed plain (un-reinforced) concrete. Some state DOT's do require full slab reinforcement, but plain un-reinforced concrete is by far the most commonly used.
http://www.pavementinteractive.org/article/pcc-pav...
http://www.pavementinteractive.org/article/jointed...
RE: Slab-on-grade maximum pour size