concrete slab question

[fried1765]

All concrete cracks; control joints in slabs put cracks where you want them, not where they want to go. I have built many slabs that after many years show no cracks outside the control joints. Use of fiber as previously mentioned reduces stress and shrinkage cracks. Low slump concrete (finishers will hate you) and water reducing additives also are key to minimize cracks. I never allow water to be added at the site unless the delivery can prove the water to be added is part of the mix design (only needed when haul time is close to maximum). Concrete batch plants will accurately apportion the ingredients as you order it. The finisher(s) are your enemy on water addition.

There are concrete guys and then there are concrete guys. A lot of science, engineering, and experimentation go into mix designs. C-94 "ready mix concrete" is a very standard product.

Prior to placing concrete everybody needs "The Contractor's Guide to Quality Concrete Construction" fourth edition. Available on Amazon. Well worth the $100.

Ron

$100 on Amazon ??

That is a mighty hefty price.
I would think a major library would have a copy, or could get a copy.

How easily things can go wrong though.
35 years ago I had a 30+ yard slab poured for my barn.
The first truck was late so I walked back up to the house (500' away) to make a brief phone call (no cell phones in those days)
When I got back to the building the 1st truck had arrived, and the finishers had already instructed the driver to add more water.
Here I am, 35 years later, still, with a big puddle spot in the floor, and many hairline cracks.
I waited for the next three trucks, and watched carefully for no additional water.

I am a former Civil Engineer, so I think I know a little about concrete.
I made a mistake!
I did not watch them every minute.

I paid only for the 30+ yds. of concrete!
I refused to pay for placement labor.
Told the finisher to take me to court if he didn't like it.
Never heard back.

 

[SandburRanch]

If it were mine on expansive soils it would have a minimum of 6" of compactable sand or gravel under footings and all sides of footers plus the same under the slab. This is all compression so rebar isn't very important if soil prep is correct. It pays to do some compaction research rather than a builder saying I've driven over it with the tractor enough so it should be just fine.