Slab question
Slab question
(OP)
I am designing a concrete slab on grade. It is going to be 4 inches thick. This slab is 23'x 60' and i decided to put a longitudinal control joint in the center (at 11.5 feet) and control joints every 12 feet transversely. I am thinking about adding #3 reinforcement but i'm not sure I even need it. I don't know if the joints will be enough...I have read about every post on this forum about slab on grade and I still cannot decide what to do...Any advice? Thanks.





RE: Slab question
4" is also a standard NY City sidewalk, in which joints are generally placed at 5'.
RE: Slab question
Bridgebuster... most areas I've been involved with in Canada, the sidewalks are 6" thick, with sawcuts at 4' centres and panels separated at 12'-16' centres. Current practice in Winnipeg, or at least a couple of locations with new sidewalks, they have omitted the tentest at 12-16 centres and only relied on sawcutting... sidewalk panels have heaved a foot from thermal movement.
RE: Slab question
RE: Slab question
I suggest that you consider two options:
1. Forget the rebar and stay with 4" thick unreinforced concrete.
2. Use the money that would have been spent on rebar to purchase more concrete and increase thickness of the unreinforced slab from 4" to 5" (or so).
www.SlideRuleEra.net
RE: Slab question
Slab on grade design is as much art as it is science. There are many acceptable ways to achieve good performance. There are also many ways to run into problems. So when you read various posts, you will find a wide range of opinions. I have found that 4" slabs with rebar work fine if they are done correctly. But besides just the thickness, reinforcing and jointing, you also need to consider many other factors like water content, aggregrate size and grading, vapor barriers, etc. Read up on the subject as much as you can and find an experienced designer to review your work.
slideruleera,
3" cover is not necessarily required for slabs on grade. 3" is the ACI 318 requirement for structural elements that are cast directly against soil and is meant to account for the irregular surface of the soil and the possibility of soil contamination in the bottom layer of concrete.
Slabs that are placed over vapor barriers and/or compacted gravel eliminate the irregular surface and contamination concerns. Also, most slabs on grade are not considered structural elements so ACI 318 does not apply anyway.
RE: Slab question
www.SlideRuleEra.net
RE: Slab question
RE: Slab question
For such thin slabs, thickness control is extremely important, coupled with early saw-cutting. Cut the joints as soon as you can use the saw without raveling the cut. That can be anywhere from 4 to 8 hours after placement. Don't wait until the next day. As for thickness control, you have a tolerance of -1/4 to +3/8 on a slab of this thickness. Since that is a total variation of 5/8", it is important that you not allow sudden transitions of thickness. This means that your subgrade must be relatively flat and it you use a plastic sheet vapor barrier, it must not have wrinkles in it.