Questions on joints for 4" concrete slab

For a 4" concrete slab, how long of a run before an expansion joint is necessary? 50', 100'?
At the expansion joints, what is the best way to maintain the two separate slabs on the same level over time. Dowel and sleeve or keyway (tongue and groove)?
For cutting of the control joints, I hear within 24 hours (green) and also 10 days ("cured") after the pour. So what is the best time to cut the control joints and why is this timing so important?
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Frank wrote:

Depends on what you are pouring. If its a sidewalk, we usually do an expansion joint every 12-15 ft. If it is a slab for a house, we don't generally put expansion joints, if it is a commercial building, the engineer will spec when and where to put the EJs, but it is usually about every 200-400 sf. Different situations need different remedies.

Sleeved smooth dowels. Sometimes sleeved on both sides, sometimes only one. Sometimes standard rebar dowels without sleeves. It is difficult if not impossible to put a keyway into a slab when you are pouring both sides of the joint at the same time.

Within 24 hours. Cutting at this time is easy, plus if the slab is going to crack, it usually does it pretty quickly after the first few days. If you wait 10 days, the cracks you are trying to control may have already happened.
But, different soils, different situations, require different things. In my history with concrete, I have seen so many different specifications that there IS no general rule you can go by. Engineers do wonders in deciding those kinds of things.
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Robert Allison
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Expansion joints every 60 feet or less in my experience. Also needed at change of dimension, use, and to prevent locking a slab.
Construction joints are for your convenience to give yourself manageable pours. They can be directed by architect or dictated by the equipment being used. Greased or sleeved slick dowels, load transfer plates, and keyway will all work. The plastic sleeves fastened to the forms sure beat drilling and fighting dowels. None of them will make up for poor subsoil preparation and compaction. All will require high concrete strength (14 or more days) before loading
Saw joints (contraction joints) need to be cut as soon as you can get on the concrete without raveling. Depending on temperature and humidity conditions, you might chance waiting to the next morning, but concrete will usually have decided where to crack by then.
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So cutting after a few day is useless?
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Yes, cutting after several days is useless other than making a pattern. The internal shrinkage cracks are already established.
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