OT---Cutting expansion joints in new concrete

My son is pouring a new concrete drive this week. He is doing the work himself, with help, and planes to cut expansion joints with my concrete cut saw with diamond blade.
There will be about 12 cuts through 4"--5" thick 12'-15' wide.
Would expansion boards be better?
Neither of us have ever done this and I would like any advise anyone has.

Cast in place expansion strips are the way to go. Open cuts will fill with debris and water. Cause you trouble in the future. Do it right the first time. With concrete a send try is expensive and labor intensive.

I would never cut all the way through! The cut is just to make it crack in a controlled straight line, if you cut through the re-bar you have reduced it's effectiveness. I think we only cut about 1 inch deep, and make sure the concrete is a consistent thickness. When they did my garage (before we bought the place) they scored it but it cracked 6 inches away from the score! I bet it's twice as thick under the score as where it cracked! That's the way the sidewalk was that I jackhammered out. Idiots!

In general concrete needs an expansion joint at no more than 90 ft if it is reinforced
it needs a contraction joint at no more than 30 ft if reinforced and the reinforcement does not pass thru the joint.
for controlled shrinkage cracking on a slab on grade
I think your spacing is ok and saw cutting to at least 1/2 the slab depth will keep the tensile/cracking stresses in the lower half

The two answers below are correct. As was said, you don't need to cut all the way through. I would cut somewhere LESS than 2", probably around 1" deep. The concrete is going to crack, and the control joint is just allowing that to happen, only on a straight line. Bob

Yes those strips look like really thick tar paper. They work fine! My dad and I poured cow pads along the driveway to feed green chop. That was in 1968 and no cracks. Also 6" deep.

If you decide to go with the expansion strips, don't use the old tar paper strips. Most redi-mix plants carry rubber strips that won't rot out in a few years.

Frankly, I don't see how the strips are a better idea than cuts if the concrete is over 4 inches thick. With a six inch slab the strip only goes through a little more than half the slab. Exactly how is the strip supposed to allow the slab to move when there's solid concrete under it? The contractor who did our 25 foot wide slab insisted on putting an expansion strip lengthwise down the center; I then cut the slab crosswise and lengthwise. We've had no problems with the slab other than cracks in a couple of spots where I should have cut it deeper.

Asphalt impregnated fibrous board, they make a rubber type now

Everyone pretty much answered your questions. Expansion joints allow for just that - expansion. Examples would be a garage floor against the driveway or a pole shed slab against the outside pad. As concrete heats it expands and would push against the another piece of concrete. Friend of mine had a house at the end of a street. No expansion joints between the street and driveway or driveway and garage floor. House was the walkout basement type. Eventually pushed on the back wall. $15,000 to reinforce the back wall and cut out the concrete to install expansion joints so it wouldn"t push on the house again. Yes, an expansion joint should go full depth of the concrete being poured. Concrete will crack. When it does the crack will more than likely go in a random fashion across the slab. Control joints are nothing more than creating a man-made weak area for the slab to crack at. Sometimes it won"t stop the crack, but it might eventually catch the crack to keep it from spreading entirely across the slab. An inch might be deep enough. Before saws everyone used a tool called a "jointer" to put roughly a 3/4 inch groove into the concrete. Curing the slab is extremely important. Keeping it moist will slow the curing process which actually helps slow hydration, which is the curing process of concrete. Burlap bags, lawn sprinklers, tarps, etc. can help keep it moist. The first few days is the most important, but a week or two would be beneficial. Hydration goes on for up to a year, but most of the strength is there after 30 days. Good luck.

Expansion joints are fine but if you're in a colder climate and you really don't want cracks, make sure it is drained. Put gravel and drain tile and crown or slope the soil toward the tile. Water is the enemy and it always wins.

I have had better luck with sawn control joints rather than fiber board strips. The saw cuts were put in one day after the pour. Also do the pour in the Fall when the sun is low in the sky and the weather is cooler to slow down the cure and prevent contraction fractures.

I've never seen concrete expand larger than it's size the day it was poured.

We quit using expansion joints years ago for anything other than a bond breaker.

Even when people are using it they always attach it with mechanical fasteners, which negates any ability to absorb the non-existent expansion.

I assume it's not an early entry saw which allows
you to cut the same day? If it's a regular saw
just make your cuts early the next morning. If it
starts to spall the edges of the cut, wait another
hour and try again.

Timing is everything, like these guys said you
only have to cut partial, next day I like to go
inch and a half deep. If it's a long pour try to
joint one by hand in the center the same day so it
doesn't crack overnight before you can cut.