How do they dowel rebar into an existing slab?
How do they dowel rebar into an existing slab?
(OP)
I am curious as to what a typical detail is when it comes it doweling rebar into an existing slab-on-grade. Do they drill a hole on the edge of the slab and epoxy rebar in the holes or do they saw cut the slab from the top and place the rebar that way? How is it usually done? Does anyone have a standard detail they would like to share or communicate to me?
Thanks!
Thanks!
Clansman
If a builder has built a house for a man and has not made his work sound, and the house which he has built has fallen down and so caused the death of the householder, that builder shall be put to death." Code of Hammurabi, c.2040 B.C.






RE: How do they dowel rebar into an existing slab?
Make sure the hole diameter is in accordance with the epoxy manufacturer's recommendations. It makes a difference in the load capacity of the dowel, particularly in tension.
RE: How do they dowel rebar into an existing slab?
Clansman
If a builder has built a house for a man and has not made his work sound, and the house which he has built has fallen down and so caused the death of the householder, that builder shall be put to death." Code of Hammurabi, c.2040 B.C.
RE: How do they dowel rebar into an existing slab?
RE: How do they dowel rebar into an existing slab?
RE: How do they dowel rebar into an existing slab?
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: How do they dowel rebar into an existing slab?
Clansman
If a builder has built a house for a man and has not made his work sound, and the house which he has built has fallen down and so caused the death of the householder, that builder shall be put to death." Code of Hammurabi, c.2040 B.C.
RE: How do they dowel rebar into an existing slab?
RE: How do they dowel rebar into an existing slab?
You can use plate dowels instead of rod dowels, particularly for thin slabs. A saw-cut is made into the side of the exposed slab, and a plate dowel is placed, then the new concrete placed adjacent. Works well for those slabs in the thickness range Mike noted.
RE: How do they dowel rebar into an existing slab?
RE: How do they dowel rebar into an existing slab?
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Whenever doweling into an existing slab on ground, I have always provided round bar dowels, 16mm diameter (5/8"), hot-dipped galvanized, 450mm long (18"), 200mm (8") into the existing slab and spaced at 1000crs (3').
I have never give any consideration to the shrinkage of the new slab or spalling of the existing slab due to inadequate edge distances during drilling.
RE: How do they dowel rebar into an existing slab?
The old slab has already done its shrinking, or most of it, and the new slab will want to shrink, both normal and parallel to the joint. The idea of diamond dowels is that shrinkage in the perpendicular direction also provides clearance to allow the parallel shrinkage to occur without stress. This can also be accomplished with square dowels with compressible material on the sides, and these are also furnished by Danley.
I haven't used plate dowels in thin slabs, and would be concerned about consolidation under the plates and also that the concrete on top of the plate would break out.
The size and spacing of dowels, regardless of the type, needs to be related to the slab thickness and loading.
RE: How do they dowel rebar into an existing slab?
Ive always used R20 dowels at 600mm centres in 150mm RC concrete pavements used for industrial applications. Ive just drilled holes and inserted the dowels, always thinking of shear transfer, never of shrinkage parallel to joint, but I guess for long joints it would be significant. Also Ive attended quite a few workshops on pavement design and the point was never discussed.
Maybe I'll bring that up in my next workshop. (It's a very good point !)
Cheers
RE: How do they dowel rebar into an existing slab?
What you have been doing is fairly typical, but the shrinkage parallel to the joint can be a problem, especially if there is some time between pours. The corners are the most vulnerable for cracking if dowels are placed too close. The Danley site which asixth referenced has some good information, and the Danley folks will probably come and give you a lunchtime presentation if you wish, and may even bring sandwiches.
RE: How do they dowel rebar into an existing slab?
Shrinkage along the joints can be a significant issue especially at the corners where a diagonal crack often forms.
Best to avoid placing too long a section at once and also other items of good practice to minimise this..
I would recommend against dowelling into a 150mm slab as it very often breaks out the concrete. Undercut the slab and pour a lip of the new slab under the existing.