Shrinkage, WWM & Synthetic fibres
Shrinkage, WWM & Synthetic fibres
(OP)
I have a 4" slab-on-grade with in-floor heating tubes for an elementary school. 6x6-10/10 WWM is placed at the bottom of the slab so that the tubes can be held in-place.
If the WWM is lifted 1/2" from the bottom will it be somewhat effective in controlling temperature/drying shrinkage? The WWM has to be located in the upper 1/3rd of the slab to be effective correct?
Basically I have to add a second layer of mesh or use synthetic fibres/ The second layer will be hard to accomodate so I don't want to go with that.
I know that many new schools in our area have been constructed with only polypropylene fibres (fibremesh) in the slab-on-grade (NO WWM except at bottom). This does nothing to control temperature shrinkage. I don't think this is good practise. Should I use a better fibre product to control long term temperature change effects?
What do you suggest.
Thanks,
P
If the WWM is lifted 1/2" from the bottom will it be somewhat effective in controlling temperature/drying shrinkage? The WWM has to be located in the upper 1/3rd of the slab to be effective correct?
Basically I have to add a second layer of mesh or use synthetic fibres/ The second layer will be hard to accomodate so I don't want to go with that.
I know that many new schools in our area have been constructed with only polypropylene fibres (fibremesh) in the slab-on-grade (NO WWM except at bottom). This does nothing to control temperature shrinkage. I don't think this is good practise. Should I use a better fibre product to control long term temperature change effects?
What do you suggest.
Thanks,
P






RE: Shrinkage, WWM & Synthetic fibres
RE: Shrinkage, WWM & Synthetic fibres
I know this is not the conventional view, but it is not mine alone. The best and most compelling argument I have seen for this theory is a paper by Cesar Kiamco in the July 1997 Concrete International magazine, entitled "A Structural Look at Slabs on Grade".
I don't think you can get 2 layers of mesh and heating tubes in a 4" slab. If you decide you must have the top layer, may have to increase thickness to say 5".
RE: Shrinkage, WWM & Synthetic fibres
I agree with hokie that reinforcing located near the bottom of the slab is effective. I would use a lot more than 6x6-10/10 though. In fact, I would use #4@18" E.W.
RE: Shrinkage, WWM & Synthetic fibres
thread507-144777: WWF vs Rebar
thread507-126594: Support of wwf in slab on grade
thread592-152445: Slab on grade-no reinforcing
RE: Shrinkage, WWM & Synthetic fibres
My sawcut spacing will be 10 feet o.c. governed by the geometry of the classrooms.
I plan to use fibremesh 300 and specify that the WWM be placed 1/2" from the bottom.
Next job I will try a 4 1/2" slab with 2 layers of mesh.
RE: Shrinkage, WWM & Synthetic fibres
You may want to consider where control joints are in the finish, unless it's carpet.
JW