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Old 06-06-2010, 07:28 AM   #16
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Pouring a patio without rebar????


Hi

Concrete is excellent in compression but useless in tension - steel reinforcement is used to provide strength in the tension zone of the concrete (area nearest the ground). Fibre possibly has some benefits but it is more likely to be in the ease of pouring but this will not stop the concrete cracking as the fibres may well stretch a little bit but the concrete will not and it will fracture.

The reason steel reinforcement corrodes is generally down to there being an insufficient cover of concrete to protect the steel, minimum cover in exposed conditions should be 2" below and 2" above the steel mesh reinforcement, which really blows a hole in having a 4" slab - need to go to a 6" slab as the reinforcement needs to be in the tensile zone and not the middle thickness (neutral zone) of the slab! If your going to go the whole hog you should have a sub-base of 4" of clean hardcore topped with aprox. 2" of compacted sand blindng.

Steel mesh(fabric) generally comes in 8ft x 16ft sheets and it is down to the builder to cut it to size on site, any overlaps should be a minimum of 14" and steel ties should be used - guage of the steel should be minimum of 3/8" diameter. You will need to space the mesh off the sand blinding by 2" and pieces of clean hardcore can be used for this purpose.

One other thing - do not over-tamp the concrete - if you do you will get what is called a 'fatty layer' develop on the surface and this may lead to surface fracturing later on!

Hope the above is of some assistance and good luck with your project

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Old 06-06-2010, 08:13 AM   #17
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Pouring a patio without rebar????


never thought we'd be approaching ' zen concrete ' in this thread

nevertheless, steel in slab reinforcement still adds only flexural strength ( bdge, elevated slab, hi-rise floors, moment loading, etc,,, in slab-on-grade, it does add strength during extreme tension stress ( green conc ) yet more benefit will be derived from placing contraction jnts in the proper pattern & in a timely fashion

impo, adding fiber's like women watching oprah - they only FEEL better & nothing's resolved steel corrodes because the conc isn't waterproof ( either according to aci specs OR no proper waterproofing coating applied,,, 2" cover rule's rarely observed especially when you have jabonies or gollywops tramping all thru the mud,,, never have seen 3/8" welded wire mesh even on hgwys, aprons, 3,000,000 gal tanks, or runways
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Old 06-06-2010, 09:11 AM   #18
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Pouring a patio without rebar????


Quote:
Originally Posted by itsreallyconc View Post
never thought we'd be approaching ' zen concrete ' in this thread

Why not, isn't that how it always goes here?

nevertheless, steel in slab reinforcement still adds only flexural strength ( bdge, elevated slab, hi-rise floors, moment loading, etc,,, in slab-on-grade, it does add strength during extreme tension stress ( green conc ) yet more benefit will be derived from placing contraction jnts in the proper pattern & in a timely fashion

I'd actually set proper curing as a higher priority than the jointing. If the compressive strength gains stay ahead of the tensile stresses, far less chance of random cracking. Better yet, skip the sawing & tool the joints in right away......

impo, adding fiber's like women watching oprah - they only FEEL better & nothing's resolved

I won't advocate mush for plastic fibers either, I really don't put much faith into them.

steel corrodes because the conc isn't waterproof ( either according to aci specs OR no proper waterproofing coating applied,,, 2" cover rule's rarely observed especially when you have jabonies or gollywops tramping all thru the mud,,,

Don't forget that there is one very important element needed for steel to corrode: Oxygen. Steel encased in concrete doesn't see much oxygen at all. As a matter of fact, I'm often time amazed to tear-out out concrete that's 40+ years old and has steel mesh in it that is less rusty than the mesh I can buy new today. The only place I see steel fail regularily in res. work is at the joints, especially those that have opened substantially through time. This is one reason (among many others) why I opt for 3/8" rebar vs. mesh : longer lifespan at joints.

never have seen 3/8" welded wire mesh even on hgwys, aprons, 3,000,000 gal tanks, or runways
Myself either, I think he may have meant 6x6x6ga. WWM? AKA roadmesh.
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Old 06-06-2010, 04:45 PM   #19
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Pouring a patio without rebar????


Hi

Got my conversion wrong - working in metric converting to imperial in the head!
Should have been 1/4" (6mm)

Regards to all!
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Old 06-08-2010, 12:34 AM   #20
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Pouring a patio without rebar????


In the Dallas metroplex, homebuilders own new subdivisions while they are being built, including the streets and sidewalks.

Of course the home builder would like to put /mesh in the sidewalks, but since the city knows they will inherit them, the force the homebuilders to put in rebar.

Guess what goes in the driveways? Mesh. Since the city is not responsible for your driveway, they are ok with mesh. Since they are responsible for the sidewalk, they require rebar.

I know this because I baught the leftover rebar from a homebuilder in a new subdivision and he explained how he had extra rebar lying around.

What does the city know?
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Old 06-08-2010, 06:38 AM   #21
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Pouring a patio without rebar????


VERY interesting question,,, don't the best & brightest always work for government ? ? ? my guess isn't compressive strength but tension ! ! ! is there much frost down there ? ? ? what do i win for being 1st & rightest ? ? ?
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Old 06-08-2010, 08:27 AM   #22
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Pouring a patio without rebar????


Someone on city council owns the rebar company.
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Old 06-08-2010, 08:59 AM   #23
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Pouring a patio without rebar????


Yeah, ya can't go wrong following the city's example.

Recently in our city they have been putting in crosswalks and speed bumps with a surface of that decorative brick veneer... about .5" thick. Should last maybe two years. Think someone's nephew owns the company?

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