Concrete Pavement Dowels
Concrete Pavement Dowels
(OP)
I am involved in the construction of a new concrete hardstand (200 mm thick [8"]). The dowels are 20 mm diameter x 400 mm long, spaced @ 300 mm on center. The center of the dowel is at 110 mm below the surface of the concrete surface. Project requirements indicate that the dowels shall be installed by "drilling and epoxy method" (drill holes after concrete is hardened, clean these holes, apply epoxy and insert the dowels). The hardstand will have 200 mm of granular well compacted base course.
My question is: Do you think about any special considerations why placement of dowels using dowel basket installed prior to paving is not allowed? What are the reasons for the "drilling and epoxy method" to be considered? I understand that dowel misalignment may be an issue during concrete placement if dowel baskets are used but this can also occur for the "drilling and epoxy method".
For dowel baskets, I think that dowel misalignment may be minimized if the dowel basket is well fixed on the base course (and also the dowel itself to the basket).
Any input will be greatly appreciated. Thanks !
My question is: Do you think about any special considerations why placement of dowels using dowel basket installed prior to paving is not allowed? What are the reasons for the "drilling and epoxy method" to be considered? I understand that dowel misalignment may be an issue during concrete placement if dowel baskets are used but this can also occur for the "drilling and epoxy method".
For dowel baskets, I think that dowel misalignment may be minimized if the dowel basket is well fixed on the base course (and also the dowel itself to the basket).
Any input will be greatly appreciated. Thanks !
RE: Concrete Pavement Dowels
Drilled dowels suffer from misalignment unless careful inspection is carried out during drilling. Using a drill guide is preferred. If you use a guide and inspect the process, drilled dowels work well. One item that is often neglected in both applications is the addition of a compressible material at the end of the slip side of the dowel.
RE: Concrete Pavement Dowels
I hear what Ron is saying, but I guess I have a hard time believing that the cross wires provide too much restraint that wouldn't be overcome by the shrinkage forces.
RE: Concrete Pavement Dowels
Can you elaborate more on the "a compressible material at the end of the slip side of the dowel". How it looks, and its function?
RE: Concrete Pavement Dowels
Placing the dowels just below the center of the slab seems odd to me and is a strong hint that the Engineer wants to squeeze in a rebar mat, probably just above the dowels. In a "thin", 200 mm slab, considering top and bottom rebar/dowel cover requirements, there is not much room remaining for rebar mat vertical construction tolerance.
If my "guess" is right, I see two outcomes:
Note: If my "guess" is wrong, I don't mind "eating crow".
Numerous interferences between the drilled holes and rebar mat. In that case, both 110mm vertical distance and the 300mm dowel spacing become a "best efforts" goal, not an enforceable requirement. May be a few "cracked" slabs along the way by attempting to drill holes at precise (but impractical) locations.
The other outcome... Contractor successfully places the rebar mat as intended and there are no drilled hole interferences.
If the Contractor can do that, he can also set dowel cages correctly and place concrete without disturbing the dowels... saving much time, trouble, risk, and the Owner's money.
Suggest taking the steps to get drill/epoxy changed to dowel baskets.
As for the reason why drill/epoxy was specified... IMHO, the designer does not significant experience with dowels and is overly impressed with a "neat" drawing, where everything fits perfectly.
www.SlideRuleEra.net
RE: Concrete Pavement Dowels
RE: Concrete Pavement Dowels
In most instances, the concrete will shrink away from the dowel as it cures. For most areas, the dowels do not expand from heat; however, the concrete does and can push the dowel. In some areas, the pavement heats up to the point that this occurs. The other advantage is that the end of the dowel does not bond to the concrete (I've inspected dowels that were greased all around except the end).
Perhaps its an unnecessary precaution, but I specify it anyway
RE: Concrete Pavement Dowels
Never thought about it, a simple and sure way the dowel will perform properly. Thanks.