Couple Concrete Pad Questions

[Stimw]

I layed out a 40' X 65' slab using one of the laser levels set up on a camera tripod and sticking it with a yard stick.
I graded it with an old 8-N Ford tractor and a scraper blade compacting with the tractor.
I formed it myself and hired 4 concrete guys to drop and finish. They had a power trowel.
At the time I was told that with fiber I didn't need rebar. If someone tells you that slap them!!
I have some experience with concrete, even drove the trucks delivering it but it was before fiber came out. I ended up with some cracks.
You need rebar and wire with it is even better.
You are better off pulling the dirt from the up hill side to level with the down hill side. Without major compacting and bracing the fill will settle.

 

[adirondackmtnman]

Show me a contractor that will sign a guarantee that your concrete will not crack, and I will show you a guy that is very desperate to get the job and will pretty much do or say whatever it takes, but he could never stand behind it.

My family has been in the concrete business my whole life, and there is no way to GUARANTEE it will not crack. One thing for sure is, 6000 will crack before 3500.

If you follow what Gary said you will be fine.

Agreed...all concrete on grade will indeed crack. The only thing you can do is try to convince it to crack at pre cut expansion joints as was stated before. Good subgrade prep definitely helps reduce cracking as less settling= less movement beneath the slab post-placement. Fiber around here(northeast NY) runs about $8/yd, but that probably varies regionally. 3000-3500PSI is quite adequate for your application. Depending on your climate, and the time of day you place your concrete, a little retarder in the mix couldn't hurt to aid in crack prevention as well, it reduces the heat of hydration, which is better overall for the concrete, especially when placed in hot weather. If feasible, keeping the surface of the concrete damp as long as possible aids proper curing as well.

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[adirondackmtnman]

I layed out a 40' X 65' slab using one of the laser levels set up on a camera tripod and sticking it with a yard stick.
I graded it with an old 8-N Ford tractor and a scraper blade compacting with the tractor.
I formed it myself and hired 4 concrete guys to drop and finish. They had a power trowel.
At the time I was told that with fiber I didn't need rebar. If someone tells you that slap them!!
I have some experience with concrete, even drove the trucks delivering it but it was before fiber came out. I ended up with some cracks.
You need rebar and wire with it is even better.
You are better off pulling the dirt from the up hill side to level with the down hill side. Without major compacting and bracing the fill will settle.

You have absolutely no need for both steel and reinforcing fibers in your concrete...and I welcome anyone to give me proof otherwise. I design this stuff for a living.

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[RDrancher]

You have absolutely no need for both steel and reinforcing fibers in your concrete...and I welcome anyone to give me proof otherwise. I design this stuff for a living.

So, are you saying that there is no benefit to using fiber in a rebar reinforced concrete mix, or are you saying one or the other?

 

[adirondackmtnman]

So, are you saying that there is no benefit to using fiber in a rebar reinforced concrete mix, or are you saying one or the other?

You won't get much benefit if any by placing steel inside this particular application in addition to fiber if you want fiber reinforced. Steel is tried and true, and fiber works REALLY well, but as was mentioned before, it can burn when power troweling, and can be a bear to get to lay down depending on the size and shape of the fiber, and the slump/workability of the concrete.

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[RDrancher]

You won't get much benefit if any by placing steel inside your particular application in addition to fiber if you want fiber reinforced. Steel is tried and true, and fiber works REALLY well, but as was mentioned before, it can burn when power troweling, and can be a bear to get to lay down depending on the size and shape of the fiber, and the slump/workability of the concrete.

I'm not the OP, but appreciate the reply.

Myself...I would never substitute fiber "only" for steel. Fiber is great at controlling plastic and drying shrinkage, and it does a great job in reducing micro cracks. What it doesn't do well is hold concrete in compression which adds flexural strength. Rebar does that quite well.

Funny that you mentioned placing and finishing problems with fiber. Back in 1987 I was pouring a parking lot for a K-mart distribution center. My concrete salesman wanted me to try this new fiber stuff in the mix. I was bull floating behind the rod men when one of them asked me why the mix was full of cat hair. :laughing: Fiber got a lot better in the years to come.

 

[adirondackmtnman]

I'm not the OP, but appreciate the reply.

Myself...I would never substitute fiber "only" for steel. Fiber is great at controlling plastic and drying shrinkage, and it does a great job in reducing micro cracks. What it doesn't do well is hold concrete in compression which adds flexural strength. Rebar does that quite well.

Funny that you mentioned placing and finishing problems with fiber. Back in 1987 I was pouring a parking lot for a K-mart distribution center. My concrete salesman wanted me to try this new fiber stuff in the mix. I was bull floating behind the rod men when one of them asked me why the mix was full of cat hair. :laughing: Fiber got a lot better in the years to come.

Yeah, if it was my building, I'd go with steel and forego the fiber, but I don't know if his benefits would outweigh the cost. I've seen a few contractors pour fiber around steel before...and when it gives them a headache flowing around the steel, they give her more water, which, as a mix designer and testing tech, always makes me cringe...on the 'cat hair' thing, that gave me a giggle, I've seen many an improperly mixed load of concrete spit a hairball out the back...Ah the joys of the gray stuff...but I still like it better than asphalt any day..

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[Tractor Seabee]

I beg to differ on "all concrete cracks". I have done concrete slabs and been the QC inspector on many concrete slab projects from 3" thick to 12" thick and there are still no cracks in many. My own driveway I did 10 years ago; 4" thick, double the glass fiber, 4,000 PSI, 3"slump, air entrained". 16' wide 60' long, control joint every 10' cross wise, and no construction joints, constant placement, broom finish. Still perfect today. The concrete contractor agreed to do it my way and no guarantee from him. To follow the process that provides those results unfortunately is not the common practice in residential light commercial practice today. For your slab, your are talking 50% more labor cost and 25% more material cost. So, bottom line is folks live with a sub standard job in the name of economics. Contractors in your market don't even know the American Concrete Association standards exist much less practice them.

Ron

 

[paulharvey]

Spider cracks are one thing, but most of that is avoided with wwf, not adding to much water, and cutting control joints with in 12-24 hours. I personnally like the look of tooled joints in broomed work, but they aren't as effective. I've always heard any crack that you can get a dime to stand up in is a "warranty" issue. Yes, concrete cracks, but when poured right on a compacted base, with WWF, you should only get the finest spider web cracks, and off coarse the controll joints.

 

[adirondackmtnman]

I beg to differ on "all concrete cracks". I have done concrete slabs and been the QC inspector on many concrete slab projects from 3" thick to 12" thick and there are still no cracks in many. My own driveway I did 10 years ago; 4" thick, double the glass fiber, 4,000 PSI, 3"slump, air entrained". 16' wide 60' long, control joint every 10' cross wise, and no construction joints, constant placement, broom finish. Still perfect today. The concrete contractor agreed to do it my way and no guarantee from him. To follow the process that provides those results unfortunately is not the common practice in residential light commercial practice today. For your slab, your are talking 50% more labor cost and 25% more material cost. So, bottom line is folks live with a sub standard job in the name of economics. Contractors in your market don't even know the American Concrete Association standards exist much less practice them.

Ron

This is there the proper control joints come into play...all concrete will crack, with the precut joints it isn't noticible, without them it will crack at the point of greatest pressure/weakest concrete. You and I come from a similar qc background, and I for one have a pipe dream that every concrete contractor would, at the very least try to understand how the product they're placing works, let alone actually READ an ASTM standard...most of them go with age-old assumptions that are not only wrong, they just plain do a disservice to their customers. This stuff is pricey, and the customer has to live with the result for a long time

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