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Re: concrete driveway: thickness ; mesh or not ?

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Re: concrete driveway: thickness ; mesh or not ? Joe 05-01-2007
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Posted by Bob Morrison on May 7, 2007, 10:13 am
In a previous post Nehmo Sergheyev wrote...
> > i think the guys in alt.building.construction, that
> > i'm crossposting to, would have more to say on the
> > topic of concrete driveways and rebar/wire mesh.
> >
> > i've seen HUGE driveways done with NO rebar at all,
> > and the surface is perfect years later. And that's
> > driving all kinds of heavy pick up trucks and trailers
> > onto it.
>

The trick to using no rebar in a slab on grade is proper subgrade
preparation. You MUST pour the slab on a properly compacted base. And,
you MUST have a proper layout of crack control joints.

I regularly specify slabs for residential garages and driveways as "5-inch
unreinforced slab on grade on 6" of 3/4" minus compacted gravel base.
Crack control joint every 150 sq.ft."

The only reason to put reinforcing steel in a slab on grade is if the soil
is very poor and cannot be properly compacted.

--
Bob Morrison, PE, SE
R L Morrison Engineering Co
Structural & Civil Engineering
Poulsbo WA
bob at rlmorrisonengr dot com

Posted by Chris Lewis on May 7, 2007, 10:45 am
> The trick to using no rebar in a slab on grade is proper subgrade
> preparation. You MUST pour the slab on a properly compacted base. And,
> you MUST have a proper layout of crack control joints.

> I regularly specify slabs for residential garages and driveways as "5-inch
> unreinforced slab on grade on 6" of 3/4" minus compacted gravel base.
> Crack control joint every 150 sq.ft."

> The only reason to put reinforcing steel in a slab on grade is if the soil
> is very poor and cannot be properly compacted.

If the OP thinks he's got a good chance to avoid having to use rebar,
using fiberglass fiber reinforcement works quite well (not as well as
full blown rebar, but...), and is _much_ cheaper than rebar or mesh.
Cheap insurance for marginal situations.
--
Chris Lewis,

Age and Treachery will Triumph over Youth and Skill
It's not just anyone who gets a Starship Cruiser class named after them.

Posted by Bob Morrison on May 7, 2007, 3:00 pm
In a previous post Chris Lewis wrote...
> If the OP thinks he's got a good chance to avoid having to use rebar,
> using fiberglass fiber reinforcement works quite well (not as well as
> full blown rebar, but...), and is _much_ cheaper than rebar or mesh.
> Cheap insurance for marginal situations.
>

The jury is still out on the effectiveness of fibermesh in preventing
random slab cracking. Fibermesh does give fuzzy slabs. In my opinion,
you will get better results by simply increasing the cement content and
reducing the water content at roughly the same cost as the fibermesh.

--
Bob Morrison, PE, SE
R L Morrison Engineering Co
Structural & Civil Engineering
Poulsbo WA
bob at rlmorrisonengr dot com

Posted by Chris Lewis on May 7, 2007, 5:36 pm
> In a previous post Chris Lewis wrote...
> > If the OP thinks he's got a good chance to avoid having to use rebar,
> > using fiberglass fiber reinforcement works quite well (not as well as
> > full blown rebar, but...), and is _much_ cheaper than rebar or mesh.
> > Cheap insurance for marginal situations.

> The jury is still out on the effectiveness of fibermesh in preventing
> random slab cracking. Fibermesh does give fuzzy slabs. In my opinion,
> you will get better results by simply increasing the cement content and
> reducing the water content at roughly the same cost as the fibermesh.

My garage slab (machine polished fibermesh, 32'x24'x4") isn't fuzzy...

The fibermesh was $50. Are you going to make an equivalent difference
with upping the concrete content by $50 worth?
--
Chris Lewis,

Age and Treachery will Triumph over Youth and Skill
It's not just anyone who gets a Starship Cruiser class named after them.

Posted by Bob Morrison on May 8, 2007, 10:30 am
In a previous post Chris Lewis wrote...
> My garage slab (machine polished fibermesh, 32'x24'x4") isn't fuzzy...
>
> The fibermesh was $50. Are you going to make an equivalent difference
> with upping the concrete content by $50 worth?
>

The slab could have been torched off to get rid of the fuzz.

An additional sack of concrete per cu. yd adds about $5 per yard. For $50
that's 10 cu yds of concrete. At 4" thick that's about 815 sq. ft of
concrete. (32x24 = 768 sq.ft).

For 5" thick the quantity req'd would be 12 cu. yds. The extra sack of
cement per yd would have cost an extra $60 vs $50. I'm pretty sure the
5" slab with extra cement will perform better than the 4" with fibermesh.

Did you use crack control joints? Compacted gravel base?

--
Bob Morrison, PE, SE
R L Morrison Engineering Co
Structural & Civil Engineering
Poulsbo WA
bob at rlmorrisonengr dot com

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