Contraction Joints In Structural Topping
Contraction Joints In Structural Topping
(OP)
Hi all.
My questions are regarding contraction joints in structural topping. I am completely new to this topic. Contraction was to lay bonded structural topping (the thickness between 25 up to 50 mm on an in-situ slab) and forgot to apply contraction joints. The topping cracked and they have to lay a new one. The slab has openings as shown on the drawings.
1. They intend to apply contraction joints every 3 m. ,every joint running along the shorter side of the room . The contraction joints will not be aligned with the openings edges. Can it be like that? Are the joints not supposed to match the edges of the openings?
2. They intend to put a mesh ,just in case. I always thought that in bonded system a mesh is not used. If it is ok to use mesh what maximum thickness would be allowed so there is not too much steel in the concrete.
3. Aren’t joints between the topping and the walls supposed to be also applied?






RE: Contraction Joints In Structural Topping
RE: Contraction Joints In Structural Topping
All they apply is 'topping' (cement+sand+water=screed?) bonded to the slab, maybe I got the terminology wrong.
I thought that we always apply joints to screeds thou?
RE: Contraction Joints In Structural Topping
A bonded concrete overlay on existing concrete should be a constant thickness. Patch and prepare the existing slab so that the overlay will be a constant thickness.
Match the location of any existing joints. Extra joints are ok.
Don't use mesh.
Proper, timely concrete curing is essential.
See pages 34 though 37 in "Guide To Concrete Overlays, Third Edition" (free .pdf) by the U.S. National Concrete Pavement Technology Center.
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RE: Contraction Joints In Structural Topping
Dik
RE: Contraction Joints In Structural Topping
SlideRuleEra Are you saying that extra contraction/control joints are ok then.
Are you saying that extra contraction/control joints are ok then.Also,when you lay topping you lay it in stages so for example you divide it into areas,lets say you put a stopper every 3 meters. So apart from those stoppers every 3meters, is it ok to put extra contraction joints every 6 meters? it is what I read in one of the guides.
Once again sorry for being awkward but I am completely new to it.
RE: Contraction Joints In Structural Topping
Dik
RE: Contraction Joints In Structural Topping
Or is this is a slab that is on the ground?
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RE: Contraction Joints In Structural Topping
Per JAE's question, I will assume the question is about a slab on grade. Extra "joints" are ok. I suggest that a name (contraction, control, expansion, etc.) not be used for the joints in the overlay. The bonded overlay must perform exactly like the underlying slab. Overlay joints are there to make that happen... that is all.
You have read other guides... suggest reading the pages noted in the guide linked to above.
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RE: Contraction Joints In Structural Topping
it is on first floor spanning between beams
RE: Contraction Joints In Structural Topping
Do you need the topping for strength or just for leveling? If for strength, then shrinkage control joints make the situation worse. You would be adding mass without adding strength.
RE: Contraction Joints In Structural Topping
I'm going to guess the structural system is beams parallel to the openings and a one-way slab spanning in the short direction. The 3m joint spacing makes a bit of sense for that. This information is also needed to answer the question properly.
RE: Contraction Joints In Structural Topping
The screed is purely for levelling purposes and beams run along the shortest side of the building (across) (obviously there are beams around the openings as well). The building is an electrical substation. Although the screed is for levelling purposes it will have to withstand quite heavy equipment (transformer) before finally placed onto the openings.