Wire mesh vs rebar

quote:I'm about to pour a concrete slab at a refinery that is a driveway for 18 wheelers.

I used a little rebar, wire mesh, and metal keyways and it's poured 11" deep of 4,000 lb concrete.

You guys are starting to worry me now.

You probably also did some pretty solid subgrade work that is almost never done on a residential project site.

As stated above, reinforcing steel is placed in concrete to provide tensile strength, because concrete has pretty much none (or at least not enough to make note of).

If you have really good subgrade and non expansive soils, you really don't even need reinforcing steel in a slab on grade - because concrete is great in compression and can resist the forces of vehicles driving on it without breaking a sweat. That is if you have really good subgrade and PI's of less than 5 or so.

And since that is almost non-existent in Texas, and since residential contractors don't really have a clue about subgrade prep, soil compaction, etc., you need to put reinforcing in to help control the cracking.

And, as stated above, all concrete cracks. It is where, and to what degree, that we can control.

Remesh is pretty much only good for very light traffic (sidewalks) and for temperature surface crack control. It provides almost zero tensile strength for anything more than foot traffic.

If you are doing a driveway, you need #4 minimum. I'd tell you to go with #5 personally, but #4 will likely be sufficient. Of course, I'd also tell you to go at least 5" thick on your slab. Most contractors want to go 4", which is really 3-1/2" since it's easy to use a 1x4 as a form.

And put the reinforcing steel in the top 1/3 of the slab, with at least 1" of cover - because the reinforcing is there to resist upward forces from expansive soil, not to really aid in downward forces from traffic. Use chairs so that the mat is properly located. Make sure you have the proper lap on your splices (42 bar diameters). I'd go at most 8" OCEW, 6" if I had a choice. Most contractors will want to go something like 12", which just barely provides enough reinforcing.

And have them at the very least bring a plate compactor and compact the subgrade beneath your driveway. I don't care how much steel you put in concrete - if you have 85% compaction or less, you might as well not even bother and go with a gravel drive. It will probably last longer.

The last factor is the concrete itself. Most residential contractors will want to use psi mix. I'd go with a psi mix and I'd pay the couple of hundred bucks to have a testing lab on site to check the temperature of the concrete when it arrives, verify batch time and drum time, do slump and make sure that the mix is right. When they are troweling it out, add the minimum amount of water necessary. I've seen some of those guys dump gallons of extra water - makes it easier to work, but also reduces the strength.

I'd also look into how you are going to cure it. Water cure is the best method, but most time consuming. Membrane cure works pretty well, but you are more apt to get temperature cracks with membrane cure.

You probably also did some pretty solid subgrade work that is almost never done on a residential project site.As stated above, reinforcing steel is placed in concrete to provide tensile strength, because concrete has pretty much none (or at least not enough to make note of).If you have really good subgrade and non expansive soils, you really don't even need reinforcing steel in a slab on grade - because concrete is great in compression and can resist the forces of vehicles driving on it without breaking a sweat. That is if you have really good subgrade and PI's of less than 5 or so.And since that is almost non-existent in Texas, and since residential contractors don't really have a clue about subgrade prep, soil compaction, etc., you need to put reinforcing in to help control the cracking.And, as stated above, all concrete cracks. It is where, and to what degree, that we can control.Remesh is pretty much only good for very light traffic (sidewalks) and for temperature surface crack control. It provides almost zero tensile strength for anything more than foot traffic.If you are doing a driveway, you need #4 minimum. I'd tell you to go with #5 personally, but #4 will likely be sufficient. Of course, I'd also tell you to go at least 5" thick on your slab. Most contractors want to go 4", which is really 3-1/2" since it's easy to use a 1x4 as a form.And put the reinforcing steel in the top 1/3 of the slab, with at least 1" of cover - because the reinforcing is there to resist upward forces from expansive soil, not to really aid in downward forces from traffic. Use chairs so that the mat is properly located. Make sure you have the proper lap on your splices (42 bar diameters). I'd go at most 8" OCEW, 6" if I had a choice. Most contractors will want to go something like 12", which just barely provides enough reinforcing.And have them at the very least bring a plate compactor and compact the subgrade beneath your driveway. I don't care how much steel you put in concrete - if you have 85% compaction or less, you might as well not even bother and go with a gravel drive. It will probably last longer.The last factor is the concrete itself. Most residential contractors will want to use psi mix. I'd go with a psi mix and I'd pay the couple of hundred bucks to have a testing lab on site to check the temperature of the concrete when it arrives, verify batch time and drum time, do slump and make sure that the mix is right. When they are troweling it out, add the minimum amount of water necessary. I've seen some of those guys dump gallons of extra water - makes it easier to work, but also reduces the strength.I'd also look into how you are going to cure it. Water cure is the best method, but most time consuming. Membrane cure works pretty well, but you are more apt to get temperature cracks with membrane cure.

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