OT Concrete reinforcement

Bonnan

Member
I've received 3 bids for some demolition and replacement of a paved area. Two bids would used wire (like stock fence) and the third recommends fiberglass concrete. Fiberglass reinforced concrete is new to me; what do you guys think?
 
What are you going to do one the paved area? What type of ground under it? I have used Wire, rebar and fiber. Each has its own use.
 
No matter what you do, you need a stable base to lay concrete on. Otherwise it will try to flex and sink unevenly. This will lead to cracking and premature failure. My suggestion is a combination of reinforcement and fiberglass feinforced concrete. And be sure it is thick enough.
 

Use the wire. It prevents the concrete from heaving if you get a crack in it in the future. I always ordered a six bag mix when pouring any flat work. It is the minimum mix that will not crack, even when driven on. As the others said, a deep well packed gravel base is essential when pouting concrete. I always ran a garden sprinkler on the gravel for twenty four hours to pack the limestone gravel we use around here.
 
Fiber will help keep the concrete from cracking, but it's not really a replacement for mesh or rebar. We have a parking area with fiber and no reinforcing, and it's held up well, but we don't drive any heavy equipment over it. Like everything else, it all "depends".

Concrete guys like fiber because it's no additional work for them. Wire mesh is a bit of a pain because you need to pull it up as you pour; it does you no good if it's laying at the bottom of the slab.

Do you use salt in the winter? If you do, it will destroy any wire mesh or rebar; better to leave it out and go with fiber.

If you're going to park heavy equipment on your slab, go thick and use wire mesh or rebar.
 
(quoted from post at 17:30:54 08/27/15) Fiber will help keep the concrete from cracking, but it's not really a replacement for mesh or rebar. We have a parking area with fiber and no reinforcing, and it's held up well, but we don't drive any heavy equipment over it. Like everything else, it all "depends".

Concrete guys like fiber because it's no additional work for them. Wire mesh is a bit of a pain because you need to pull it up as you pour; it does you no good if it's laying at the bottom of the slab.

Do you use salt in the winter? If you do, it will destroy any wire mesh or rebar; better to leave it out and go with fiber.

If you're going to park heavy equipment on your slab, go thick and use wire mesh or rebar.

How does the salt get at the rebar in properly mixed, reinforced, and placed concrete?
 
Very simple, concrete has capillaries, its porous. When the deformed metal bars, (rebar) are too close to the edge of the slab, column, pier, etc. it penetrates through the capillaries, then reacts with the steel. When steel rusts like this, it will expand many times its size, and literally spall, the concrete. It was a problem in NYS with bridge designs way back when. They use epoxy coated rebar now. I have read about electrolysis, where they use am electrical current to prevent the oxidation from happening.
 
Would not have fiber concrete if it was half the price. Use wire or 1/2 rebar going both ways if you can afford it. If it is not in an area where it will have heavy loads on 2 ft centers will work. Use 4K or 5K concrete. The base is very important.
 
I've had it happen on a DM model Mack truck, double frame, between either the members or the frame and the sileage body frame, it cracked the frame, the build up of heavy rust flake was incredible. The truck was always serviced at a shop that specialized in these kinds of trucks, the mechanic there said to clear those built up flakes, given what they do, he fixed the frame on this truck numerous times over the years, eventually it was sold, went to another farm for off road and or field work.
 
Do whichever of those various reinforcements you choose, but know concrete will crack. Settlement or curing or shrinkage cracks, call it what youwill, it WILL crack. You cannot stop it. To keep the cracks where you want, so it looks unobtrusive, so it doesn't look all ugly and busted up looking, have your contractor saw cut it. Any competent contractor WILL do that. Whatever else you do, saw-cut the slab the same day you pour. Saw cut 1/4 of the thickness, to 1/3 of the thickness. About every 15' x 15'. It'll look just fine. The cracks will follow the grooves, you'll never know.
 
We used fiber in two slabs, one 1997, one 2003. No cracks outside the control joints in either. Both had a winter of exposure on the fill prior to pouring- support and room to expand/contract are important. Oh, yeah, like plumbing's three rules, concrete has them as well- it WILL get hard, it WILL crack, and the only puddle spot WILL be in the worst possible place (i.e. right where your wife exits the vehicle).
 
Concrete cracks and I have seen that when it does that wire rusts away very quickly, if want it to last use rebar.
 
Cattle panels work and are easy to work with. But no matter what type of rebar you decide to use. Make sure it's up in the concrete. Support it with a brick or whatever to keep it in the middle of the pour. Doesn't do much good if it's laying on the ground and "lifting as you pour" doesn't really work.
 
Fiber is better than wire but with either you need rebar under the base.The main thing is
finishing and pouring.I worked at a concrete plant for 25 years and I'd say easily
95% of non commerical,non inspected concrete is poured out of spec.NEVER listen to a finisher as all they want to do is get it too wet so its easy to pour.Get a independent inspector and make it plain to the finisher and the concrete supplier that only concrete thats in spec will be accepted and poured.
 
Appreciate the input; nothing better than all the experiences out there! BillyNY I've seen plenty of that rebar expansion problem here in Pa. Three bids so far range from $6 to $9 per sq ft for 4.5in, 4k concrete on 2B limestone base. Have yet to get price from the fiberglass guy.
 
I put 6 full inches of fiber reinforced concrete in my new shop building 12 years ago. I never heard of it till then, friends of mine were professional concrete workers, they suggested it, they installed it, they backed it. It has worked well, I have had 24000lb crawlers down to lawnmowers on it. so far the only cracks are where they cut it.
 
>How does the salt get at the rebar in properly mixed, reinforced, and placed concrete?

Through cracks and control joints. If salt couldn't get to rebar, we in the rust belt wouldn't be dealing with construction delays every summer as crews cut out and replace the all the highway expansion joints.
 

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