Raft Foundation on Grade Expension Joints ???
Raft Foundation on Grade Expension Joints ???
(OP)
Do I need to provide expansion joint in on grade raft foundation, if the area of slab is approximately 10000 sqm (100m x 100m) and thickness of slab foundation is 225mm. this slab foundation is for double storey light gauge steel hospital building.
However the maximum pouring per day is limited to 200 cum which mean there will be total 11 construction joints in whole foundation slab.
The second question is that, there is 100 mm finishing concrete on raft foundation so do I need to provide the controlled joint in finishing concrete too at same location ???
However the maximum pouring per day is limited to 200 cum which mean there will be total 11 construction joints in whole foundation slab.
The second question is that, there is 100 mm finishing concrete on raft foundation so do I need to provide the controlled joint in finishing concrete too at same location ???






RE: Raft Foundation on Grade Expension Joints ???
36(0.225 m) = 8.1 m. Thus you want control joints spaced between the construction joints by no more than 8m.
Lay out the pours first, then lay out the control joints. Make sure to have a joint connecting into any re-entrant corners. Also, make sure you have sufficient time between pours for the concrete to set and to prepare the joint surface. You will need control joints in the topping slab also, though probably not at the same locations.
RE: Raft Foundation on Grade Expension Joints ???
In addition, the main reason to provide a control joint is to "control" the location of the cracks in a straight, controlled line to allow joint fillers, etc. for maintenance and appearance reasons.
None of that is necessary in a mat foundation.
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RE: Raft Foundation on Grade Expension Joints ???
RE: Raft Foundation on Grade Expension Joints ???
RE: Raft Foundation on Grade Expension Joints ???
Even so, with a "mat" foundation with reinforcement top and bottom, despite any thickness, the need for a CJ is only there to control the location of the cracks - not to prevent them or somehow make the mat function better.
If the mat is buried and never seen, I see no reason to worry about a diagonal crack vs. a straight crack - both of which are kept closed with the rebar.
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RE: Raft Foundation on Grade Expension Joints ???
RE: Raft Foundation on Grade Expension Joints ???
i am using the minimum area of steel for my raft footing is 0.18% top reinforcement only (which mean 8mm dia @ 125 mm spacing c/c)and bottom reinforcement i am only placing under the load bearing wall in 1 m span as shown below (bottom reinforced calculated as strip footing method).
RE: Raft Foundation on Grade Expension Joints ???
Question - why are you limited to only 200 m3 per day? Is this a restriction due to "noise" or due to permitted working hours or availability of equipment and or batching plant capability? I would think that you should be able to do a continuous placement with enough pumps and proper sequencing of work - if using 500 mm thick slab - it would only be about 5,000 m3.
RE: Raft Foundation on Grade Expension Joints ???
2) That small amount of reinforcement will do little to control shrinkage cracks, but perhaps the cracks don't matter.
RE: Raft Foundation on Grade Expension Joints ???
RE: Raft Foundation on Grade Expension Joints ???
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