I am going to have my asphalt driveway removed and replaced by a
concrete driveway.
The driveway is about 1000 sq ft, with some slope.
I have a couple of bids already in. By code, it will be 6" at street.
One contractor suggested to go with 5" instead of the typical 4" for
an extra $550. Is that worth the extra expense ?
I was also wondering whether I should (or not) add wire or fiber mesh.
Somehow, I was told by one contractor no charge for that. Why would
they do it for free, and what's the benefits ?

thanks.

Fred.

Just going from my own research here so I'm also waiting for others to pipe
in but, the mesh or wire holds the concrete together and keeps it from
cracking. I'd also recommend having them add the "cuts" during the pour
instead of coming back a few days later to cut the dry concrete. When I do
my driveway I'll be adding either the mesh or fibre reinforcement. Possible
some ash to give it some colour. As far as the extra inch of concrete this
is what I figured out.

1) Adding an inch of concrete doesn't really change the forming or labour
involved.
2) 1 Cubic Yard = $120 around here anyway
3) 1 Cubic Yard @ 1" thick = 324 SQF
4) so the cost of extra concrete should be about $370





"fredinstl" wrote in message
ups.com...
I am going to have my asphalt driveway removed and replaced by a
concrete driveway.
The driveway is about 1000 sq ft, with some slope.
I have a couple of bids already in. By code, it will be 6" at street.
One contractor suggested to go with 5" instead of the typical 4" for
an extra $550. Is that worth the extra expense ?
I was also wondering whether I should (or not) add wire or fiber mesh.
Somehow, I was told by one contractor no charge for that. Why would
they do it for free, and what's the benefits ?

thanks.

Fred.

On May 1, 9:26 am, fredinstl wrote:
I am going to have my asphalt driveway removed and replaced by a
concrete driveway.
The driveway is about 1000 sq ft, with some slope.
I have a couple of bids already in. By code, it will be 6" at street.
One contractor suggested to go with 5" instead of the typical 4" for
an extra $550. Is that worth the extra expense ?
I was also wondering whether I should (or not) add wire or fiber mesh.
Somehow, I was told by one contractor no charge for that. Why would
they do it for free, and what's the benefits ?

thanks.

Fred.

Some form of reinforcing is needed because while concrete is extremely
strong in compression it is weak in tension. Steel is very strong in
tension and the two combined are far more durable. Odds are the
contractor who is bidding the job would not consider pouring a
driveway without reinforcement. In the long run it's his reputation.
An extra inch of thickness adds 3 cu yds of concrete to the 1000sf job
and might mean a truck is less likely to damage the slab.
You want a well compacted surface before the pour, and you want to
keep it moist for a month after the pour to develop it's best strength.

It takes less than two yards of concrete to add an inch to 1000 square feet,
so the $550 is out of line. Also, you'll want at least 5" and 1/2" rebar
on 2' centers each direction. the mesh will do nothing. For comparison, I
had a 1200' area covered with 5" and the above described rebar for $2700.
Don't let 'em stab ya, call several flatwork companies. There are plenty
out there.

--
Steve Barker




"fredinstl" wrote in message
ups.com...
I am going to have my asphalt driveway removed and replaced by a
concrete driveway.
The driveway is about 1000 sq ft, with some slope.
I have a couple of bids already in. By code, it will be 6" at street.
One contractor suggested to go with 5" instead of the typical 4" for
an extra $550. Is that worth the extra expense ?
I was also wondering whether I should (or not) add wire or fiber mesh.
Somehow, I was told by one contractor no charge for that. Why would
they do it for free, and what's the benefits ?

thanks.

Fred.

I calculated wrong. An additional ONE inch on 1000 sq ft. will require
right at 3 yards. So the $550 is still a bit steep. Around here (KC area)
concrete is right at $100 a yard with calcium and hot water. Probably a bit
cheaper for a summer mix.

--
Steve Barker




"fredinstl" wrote in message
ups.com...
I am going to have my asphalt driveway removed and replaced by a
concrete driveway.
The driveway is about 1000 sq ft, with some slope.
I have a couple of bids already in. By code, it will be 6" at street.
One contractor suggested to go with 5" instead of the typical 4" for
an extra $550. Is that worth the extra expense ?
I was also wondering whether I should (or not) add wire or fiber mesh.
Somehow, I was told by one contractor no charge for that. Why would
they do it for free, and what's the benefits ?

thanks.

Fred.

"HotRdd" wrote in message
...
Just going from my own research here so I'm also waiting for others to
pipe
in but, the mesh or wire holds the concrete together and keeps it from
cracking.


okay, i'll "pipe in".... rebar / wire mesh on a concrete
driveway is a waste of money !

the key is preparation of the ground below it.

presuming the contractor puts in rebar / wire mesh,
what's he using to hold them up during the pour ?

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.

fredinstl wrote:
I am going to have my asphalt driveway removed and replaced by a
concrete driveway.
The driveway is about 1000 sq ft, with some slope.
I have a couple of bids already in. By code, it will be 6" at street.
One contractor suggested to go with 5" instead of the typical 4" for
an extra $550. Is that worth the extra expense ?
I was also wondering whether I should (or not) add wire or fiber mesh.
Somehow, I was told by one contractor no charge for that. Why would
they do it for free, and what's the benefits ?

Can't imagine what fiber mesh is good for. Wire or (better) rebar
accomplishes the following:

When there's a slight perturbation in the ground, or freezing/thawing
cycles, the concrete cracks. The rebar prevents the opposite sides of the
crack from moving vertically or horizontally. In other words, you simply
have a hairline crack instead of a two-inch step or a one-inch gap.

There are often posts here about what to use to fill a gap in a concrete
drive. In ALL cases, it's a drive without rebar.

In article , Joe says...


"HotRdd" wrote in message
...
Just going from my own research here so I'm also waiting for others to
pipe
in but, the mesh or wire holds the concrete together and keeps it from
cracking.


okay, i'll "pipe in".... rebar / wire mesh on a concrete
driveway is a waste of money !

the key is preparation of the ground below it.

presuming the contractor puts in rebar / wire mesh,
what's he using to hold them up during the pour ?

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.

You can use the wire mesh if you wish. The concrete is poured over it while the
concrete finisher walks into the wet cement and hooks it up off the bottom. I
prefer to pour with the heaviest psi concrete that I can get and have glass
mixed in it. Thickness is important. Some folks just lay 2"X4" lumber on the
ground and pour cement to that height (3 1/2"). You want at least 4". If you
can find a concrete supplier who will mix to DOT standards you won't have any
problems and you won't need to add anything to the concrete.

fredinstl wrote:

I was also wondering whether I should (or not) add wire or fiber mesh.
Somehow, I was told by one contractor no charge for that. Why would
they do it for free, and what's the benefits ?


In my area they are using a lot of concrete with fiberglass fibers in
the mix. It does the same thing as wire mesh and rebar - keeps any
small cracks from becoming big cracks. I have a double wide drive, the
original side with concrete/wire and the other newer side with
fiberglass imbedded concrete only. After 14 years of comparison,
there is no structural difference between the two sides.
-KC

"Mike Hammer" wrote in message
...
In article , Joe says...


"HotRdd" wrote in message
...
Just going from my own research here so I'm also waiting for others to
pipe
in but, the mesh or wire holds the concrete together and keeps it from
cracking.


okay, i'll "pipe in".... rebar / wire mesh on a concrete
driveway is a waste of money !

the key is preparation of the ground below it.

presuming the contractor puts in rebar / wire mesh,
what's he using to hold them up during the pour ?

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.

You can use the wire mesh if you wish. The concrete is poured over it
while the
concrete finisher walks into the wet cement and hooks it up off the
bottom. I
prefer to pour with the heaviest psi concrete that I can get and have
glass
mixed in it. Thickness is important. Some folks just lay 2"X4" lumber on
the
ground and pour cement to that height (3 1/2"). You want at least 4". If
you
can find a concrete supplier who will mix to DOT standards you won't have
any
problems and you won't need to add anything to the concrete.


2 replies to an unknown OP, not listed by the news server for this newsgroup
(alt.building.construction).

3" of compressed roadbase is common under a concrete driveway around these
parts. Most use 3/8 tied rebar vice mesh wire. 2X4 forms are not unusual
here. They do dig up for 6" deep X 8" wide beams on the perimeter, rebared
too. 10'-12' sections allowing for expansion is common. Tying to the
street is critical. How they setup the apron and its reinforcement can make
or break it when a car creeps off the edge of the driveway.

Last heavy vehicle on this driveway of mine, same method of construction,
was a Dixie type dumptruck hauling 12 yds of sandy loam to my site. No
apparent damage.
--
Dave

Apathy and denial are close cousins

In article .net, Dave says...

"Mike Hammer" wrote in message
...
In article , Joe says...


"HotRdd" wrote in message
...
Just going from my own research here so I'm also waiting for others to
pipe
in but, the mesh or wire holds the concrete together and keeps it from
cracking.


okay, i'll "pipe in".... rebar / wire mesh on a concrete
driveway is a waste of money !

the key is preparation of the ground below it.

presuming the contractor puts in rebar / wire mesh,
what's he using to hold them up during the pour ?

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.

You can use the wire mesh if you wish. The concrete is poured over it
while the
concrete finisher walks into the wet cement and hooks it up off the
bottom. I
prefer to pour with the heaviest psi concrete that I can get and have
glass
mixed in it. Thickness is important. Some folks just lay 2"X4" lumber on
the
ground and pour cement to that height (3 1/2"). You want at least 4". If
you
can find a concrete supplier who will mix to DOT standards you won't have
any
problems and you won't need to add anything to the concrete.


2 replies to an unknown OP, not listed by the news server for this newsgroup
(alt.building.construction).

3" of compressed roadbase is common under a concrete driveway around these
parts. Most use 3/8 tied rebar vice mesh wire. 2X4 forms are not unusual
here. They do dig up for 6" deep X 8" wide beams on the perimeter, rebared
too. 10'-12' sections allowing for expansion is common. Tying to the
street is critical. How they setup the apron and its reinforcement can make
or break it when a car creeps off the edge of the driveway.

Last heavy vehicle on this driveway of mine, same method of construction,
was a Dixie type dumptruck hauling 12 yds of sandy loam to my site. No
apparent damage.

Its interesting to read about the different ways something is constructed
depending upon where one lives.

On May 1, 10:38 am, "Joe" wrote:
"HotRdd" wrote in message

...

Just going from my own research here so I'm also waiting for others to
pipe
in but, the mesh or wire holds the concrete together and keeps it from
cracking.

okay, i'll "pipe in".... rebar / wire mesh on a concrete
driveway is a waste of money !

the key is preparation of the ground below it.

presuming the contractor puts in rebar / wire mesh,
what's he using to hold them up during the pour ?

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.

Pressure on the surface of a slab will put the bottom of the slab in
tension, that is, it will tend to stretch the bottom. Thus, metal,
rebar, or to a lesser degree mesh, which is stronger in tension than
concrete, will help prevent the slab from failing.

Seeing a slab made in a particular way is just anecdotal. The people
who did it may not have known how to, or wanted to, do the job
properly. A knowledgeable eye will see bad practices and mistakes all
over the place.

Generally, you can hold rebar up with bricks or chairs specially made
for the purpose .


--
(||) Nehmo (||)

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

According to Bob Morrison :
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.

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

According to Bob Morrison :
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.

On Mon, 07 May 2007 14:45:37 -0000, (Chris
Lewis) wrote:

According to Bob Morrison :
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.


I thought the point of the fiberglass was to limit spalling.
Does it really increase the tensile strength of concrete?

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

According to Bob Morrison :
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.

It wasn't. I was working in/around the site the entire day.

[Contractor hired to extend skirt on pool, lay floor in garage, and
a bit of landscaping (timbers). Contractor prepped the forms and
base, and brought in a concrete sub contractor to install/finish
the concrete.]

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).

I wish I knew what the concrete was spec'd at. I believe it was
4K PSI, and I know it was air-entrained (pretty much necessary in
this climate).

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.

The additional concrete to go to 5" (2 yards) plus the extra
sack per yard would have been a lot more than $60.

Did you use crack control joints? Compacted gravel base?

The garage (around 9 years old) had a dirt floor - it was somewhat
sunken, so very little if any of it was excavated. Probably about
4" of gravel was slung in. I don't remember whether they used
a plate compactor, but they probably did. Above that was placed
1 1/2" of sub-concrete-rated foamboard (thermal break, it's used more
as a workshop), and the concrete was wheelbarrowed in/formed.

The concrete sub (crew of three) then did a couple of passes over it
with a polisher over the next 4-5 hours. The polisher more than likely
battered down/rubbed off anything much in the way of fuzz.

It's only recently that I've noticed that there's fibermesh in it.

Very relaxing day for all concerned, we all cooled off in the pool
after the main pour and between polishing passes, and had a beer
near the end. The sub's kid (around 5) got to play with someone
his own age rather than be cooped up in the truck all day. Sub:
"nicest job we've had in years!" ;-)

Asked about control joints, the sub said that given the nature of
the site (gravel over undisturbed soil), and the fibermesh,
it was entirely unnecessary. But the contractor had a concrete
saw onsite anyway (other part of the job was extending the skirt around
a pool which needed the relief cuts more) so, the concrete sub told
him to put two cuts in the floor midway along the walls - the floor
was quartered. I don't think the cuts have cracked, and nothing
has moved, even the concrete that was formed from the slab over
the foundation lip below the two garage doors is completely intact.

Our area is somewhat infamous for very soft soil (the dreaded
"Dunrobin Sand"), and obviously the contractor did a very good
job with the base.
--
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.

In a previous post Goedjn wrote...
I thought the point of the fiberglass was to limit spalling.
Does it really increase the tensile strength of concrete?


Some manufacturers claim it does. As I said earlier, the jury is still
out on whether or not fibermesh helps slabs resist random cracking.

I am of the opinion that it may help a little, but not enough to warrant
the cost. I prefer to increase the strength of the concrete the old
fashioned way: add cement and reduce water content. And, saw cut crack
control joints as soon the concrete is hard enough to walk on without
leaving marks (4-12 hours).

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

According to Goedjn :

I thought the point of the fiberglass was to limit spalling.
Does it really increase the tensile strength of concrete?

Air entrainment (and being careful with making sure you have
proper mixing/good quality materials) is the primary cure for
spalling. Fibermesh is supposed to prevent cracking like
rebar does. However, some suppliers suggest/say that fibermesh
helps limit spalling, early cracking, resistance to chipping
and improves surface durability too.

Obviously the suppliers have an incentive to tout the benefits,
but the existance of industry (eg: ASTM) tests to show the
actual improvement shows there must be some truth in it.

I have no doubt that steel mesh or full rebar (eg: stress concrete)
is better than fibermesh in terms of brute strength, but
fibermesh is very cheap compared to rebar, and is a good choice
in situations where you want a little more reassurance with
situation that doesn't really need steel.

I'll be doing something similar when I experiment with making
some "hypertufa". The recipe calls for 2 parts portland cement,
three parts sifted peat and three parts perlite. And a "handful"
of concrete fibermesh (a cup loosely packed for 5 gal of dry
ingrediants).

[Making some synthetic rocks to stick on top of cedar log
fence posts.]
--
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.

Bob Morrison wrote:
In a previous post Goedjn wrote...

I thought the point of the fiberglass was to limit spalling.
Does it really increase the tensile strength of concrete?



Some manufacturers claim it does. As I said earlier, the jury is still
out on whether or not fibermesh helps slabs resist random cracking.

I am of the opinion that it may help a little, but not enough to warrant
the cost. I prefer to increase the strength of the concrete the old
fashioned way: add cement and reduce water content. And, saw cut crack
control joints as soon the concrete is hard enough to walk on without
leaving marks (4-12 hours).


When I first came into contact with fibermesh (about 20 years
ago), it was limited to a couple of uses. We added it to
concrete for apartment balcony slabs and sometimes to
sidewalks. In the case of the balconies, we would pour these
at a thickness of 2" to 3". Not really enough room for any
other kind of reinforcement and chicken wire was way too
difficult to work with. The sidewalks had WWM, but the
fibermesh was added to help eliminate surface cracks.

In no way was it ever represented as a substitute for steel
reinforcement. Every time I hear that, I just have to laugh.

It may be ok in some areas, but here we have expansive soils,
rock, etc. that makes reinforcing steel absolutely necessary.

Someone mentioned that highways were constructed with
fibermesh only. They are building numerous highways here and
I have examined several of the projects under construction.
Here they use #5 rebars 1' OC with a 7" thickness, 5,000 PSI
concrete.

I will ask why they don't just use fibermesh. They could
probably use a good laugh.

--
Robert Allison
Rimshot, Inc.
Georgetown, TX

In a previous post Chris Lewis wrote...
The additional concrete to go to 5" (2 yards) plus the extra
sack per yard would have been a lot more than $60.


Right you are. Guess I was thinking about something else when I wrote
that. Gotta be more careful g.


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

"Bob Morrison" wrote in message
k.net...
In a previous post Goedjn wrote...
I thought the point of the fiberglass was to limit spalling.
Does it really increase the tensile strength of concrete?


Some manufacturers claim it does. As I said earlier, the jury is still
out on whether or not fibermesh helps slabs resist random cracking.

I am of the opinion that it may help a little, but not enough to warrant
the cost. I prefer to increase the strength of the concrete the old
fashioned way: add cement and reduce water content. And, saw cut crack
control joints as soon the concrete is hard enough to walk on without
leaving marks (4-12 hours).

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

Bob;

I worked on the revision project at the Seattle Center fountain back when I
worked with TRA. The fibermesh additive was used in the slab on grade
around the fountain. I heard that it has worked quite well. Now my
interest is up, haven't visited there in quite a while guess I will have to
see if cracks are not seen or abundant. :-)).

Chuck...

__________________________________________________ __________
Charles I. Dinsmore, PE SE RA, M.ASCE ~

Bob Morrison wrote:

The jury is still out on the effectiveness of fibermesh in preventing
random slab cracking. Fibermesh does give fuzzy slabs.

any experiences with other types of fibers in concrete?

I have heard polypropelene fibers are too soft and slippery to do much
good, but PVA fibers bond well to the cement matrix and help the
performance. I have played with PVA fibers in mortar mixes in the lab
with some success.

also, I have always wondered if there is alkalai silicate reactions with
the glass fibers. I remember reading somewhere that S-glass was best in
concrete... sorry no reference :|

replying to HotRdd, MDCraft General Contractor wrote:
So sorry to disagree with you statement concerning the mesh, wire or
fiberglass. It does NOT keep it from cracking. It keeps it from falling
lower, creating a trip hazard between the two pieces where the crack has
occurred. "Concrete is guaranteed to crack", That's on my contracts and I see
on new contracts as well. The closest additive that keeps it together better
and resist cracking would be the fiberglass since it is throughout the
concrete mix before it's poured out into the area desired.
The so called "cuts" during the pour are not "cuts" but trailed in control
joints. Meaning, hopefully when the concrete cracks it will crack at the
weakest place. Since the control joints are basically thinner concrete, it's
allowing the crack to run inside the control joint and not be as noticeable.
A "cut" joint can only be used when the concrete has dried enough for the
blade to saw the concrete and rock inside the concrete and leave a nice clean
edge. It's also used on concrete that is walked often or used with items
moved across the floor. It's a smoother transition rather than a trialed in
control joint, because it's smaller.
Lastly the additional concrete thickness does change the forming expense, why
you ask. A typical 2x4 is only 3.5" wide therefore the contractor has to use
2x6 which is 5.5" wide to handle the additional concrete depth as well as the
pressure applied to the formed walls, as the thicker concrete is heavier or
stronger side load.

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replying to Joe, MDCraft General Contractor wrote:
True, however the thickness makes a big difference on stability of the pour

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replying to Nehmo Sergheyev, MDCraft General Contractor wrote:
Just remember, steel or mesh will not help prevent the slab from failing. It
will only hold the two separated pieces from the crack from falling, not
failing. Fiberglass, since it is throughout the concrete mixture will assist
in the pour not cracking but as in our contracts the concrete itself is
"Guaranteed to Crack" when and where is the unknown. I have concrete pours
that have zero cracks after 13 years of being poured. I have some pours, few
thank goodness, that have cracks we are amazed as to why it cracked and how
the crack actually ran.

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