Tell me what you see here?

[Macinnis]

I don't expect rebar to prevent cracking. I expect it to prevent movement after the cracking.

Yeah, I didn’t communicate correctly.

I got this from quite possibly the best concrete thread ever. This guy seems to really know his stuff... The Concrete Underground's Guide to Floor Slabs - The Garage Journal Board

Reinforcing - Concrete is stronger in compression than it is in tension i.e. it's harder to crush concrete than it is to pull it apart. Steel reinforcing is used to increase concrete's tensile strength. Many people apply this principle to slabs on grade and assume that steel reinforcing will prevent cracking and make the slab stronger. Unfortunately neither is really true.

The most common cause of cracking is tension from drying shrinkage. Reinforcing won't stop your slab from shrinking or prevent shrinkage cracks. In fact, reinforcing can actually increase the likelihood of cracks by restraining the slab from contracting inward as shrinkage occurs.

Reinforcing doesn't make your slab stronger because it's passive i.e. it doesn't come under load until the concrete has already cracked. Since a typical slab isn't thick enough to act like a beam, it simply 'bends' and transfers loads to the base below. If the base can't take the load, the concrete will crack.

What reinforcing will do is keep cracks - whether they are random shrinkage cracks, the cracks in the bottom of your control joints or God forbid, structural cracks - from opening up thereby maintaining the integrity of the slab. Think of steel reinforcing as crack restraint rather than crack prevention.

Is steel reinforcing absolutely necessary? Not really. For most residential slabs placed on a solid base, it's optional. If you limit shrinkage and cut timely, properly spaced control joints, the cracks below won't get very wide and aggregate interlock will keep them from displacing. Many, however will want the added insurance of reinforcing.

Slab reinforcing can be either rebar or welded wire fabric (WWF), often referred to as wire mesh. The primary advantage of rebar over WWF is that it is more rigid and thus easier to support. If using rebar, I’d suggest #3 bars at 18” o.c. supported every 3’ or #4’s at 24” o.c. supported every 4’.

If you decide to use WWF, buy sheets rather than rolls so it will lay flat. Use WWF with a heavier gauge wire such 6x6-W2.9xW2.9 that will span between supports better. Overlap the sheets 6" and stagger the runs to avoid building up too much thickness at the overlaps. You'll need to support mesh every 3' or so - don't let your finisher convince you he can pull the wire off the ground as he places.

Support your reinforcing in the middle third of the slab. There are many products available to do this such as concrete dobies, metal slab bolster or plastic chairs. Make sure your supports can stand up to finishers walking on them and that they don't poke through your vapor barrier.

If you are placing a load bearing monolithic slab, I'd recommend using rebar including a couple bars in the bottom of the thickened haunch. Floating slabs are subject to more movement and rebar will hold everything together.

Fibermesh These are fiberglass strands that are mixed in with the concrete and advertised to prevent cracking. It is often discussed as an alternative to steel reinforcing but it performs an entirely different function. Fiber minimizes early age shrinkage cracks and theoretically allows wider control joint spacing but it won't hold cracks together once they occur.

 

[Hay Dude]

Thats a pretty good summary and how I was taught about different methods of reinforcing.
The way I look at it, its YOUR work on display. Will your concrete crack? Lets hope not, but maybe it will. Nobody really knows. When it does, can you give yourself or your customer the assurance that the crack wont expand and become really ugly or structurally unsound?
I install mesh mats and rebar and order fiber. Lot less costly than removing the slab and starting over. Of course, proper ground preparation and proper concrete mix is a given, but adding reinforcement lets the customer know you care and gave it your best and left nothing out.

 

[Industrial Toys]

Interesting read on the reinforcing. Not quite sure I agree. The building inspector for my driveshed was a real stickler for rebar. A lot of it, and in the right places. Particularly as the buidling was set into a hillside. I find it hard to believe that all this rebar does nothing, if the concrete has not cracked.



Corner of building into hillside. Paint cans are for various utility lines.

 

[Streetcar]

This is a wall not slab on grade. Two totally different structures

Interesting read on the reinforcing. Not quite sure I agree. The building inspector for my driveshed was a real stickler for rebar. A lot of it, and in the right places. Particularly as the buidling was set into a hillside. I find it hard to believe that all this rebar does nothing, if the concrete has not cracked.

View attachment 664659

Corner of building into hillside. Paint cans are for various utility lines.

 

[Industrial Toys]

When it comes to concrete, tension is tension and compression is compression, regardless of orientation.

 

[Red Horse]

Beat to death but another opinion.
-no doubt too wet, then again if you subscribe to "water seeks its own level" that works, forget about strength, no need for screed bars that you have to pull up before floor sets and you have to pull and fill with excess material you have kept in wheel barrows- you get what you pay for.
-Sand with no compaction?????
-Rebar in sand? How about heavy wire mesh on chairs and then as you are pouring someone is pulling wire up selectively to get wire off base material where
it is too far from chairs.
-No control cuts at 10' centers max cut while concrete is setting and very green Slab like that will crack for sure.

 

[Steppenwolfe]

The dude poured his own slab, for himself. He didn't break any laws of nature doing so and seemed quite happy with the outcome. More power to him.

 

[Red Horse]

No one said he broke any laws. I like to think the value of TBN is it is always a great learning experience.:thumbsup:

 

[ovrszd]

The dude poured his own slab, for himself. He didn't break any laws of nature doing so and seemed quite happy with the outcome. More power to him.

He hired a company to pour his concrete. Professionals. The discussion has been about their procedures.

 

[Hay Dude]

The dude poured his own slab, for himself. He didn't break any laws of nature doing so and seemed quite happy with the outcome. More power to him.

I thought he hired a concrete contractor to do it? The only thing I saw him do is walk around taking a selfie videos about his wifes concrete curb he had to do for her.