Cost of concrete driveway
AndyS
I just got a bid on a 310 long driveway, 14 feet wide.
It is to be 4" thick with rebar 18" OC.
The bid is for $2.65 per sq foot.
Is this a competitive bid ???
The area is North Texas
Andy in Eureka
Robert Allison
That is way cheap. And way too thin. I would go with at
least 5" of concrete for a driveway. Sidewalks are 4" thick.
Does that include base and prep work? To give you an example,
for flatwork like that, the going rate around here is about
5-6.00 a square foot with base and prep. I would be careful
about the prep especially. Without it, you are going to be
unhappy.
--
Robert Allison
Rimshot, Inc.
Georgetown, TX
RicodJour
> AndyS wrote:
>
> > I just got a bid on a 310 long driveway, 14 feet wide.
> > It is to be 4" thick with rebar 18" OC.
> > The bid is for $2.65 per sq foot.
> > Is this a competitive bid ???
> > The area is North Texas
> >
> > Andy in Eureka
> >
>
> That is way cheap. And way too thin. I would go with at
> least 5" of concrete for a driveway. Sidewalks are 4" thick.
>
> Does that include base and prep work? To give you an example,
> for flatwork like that, the going rate around here is about
> 5-6.00 a square foot with base and prep. I would be careful
> about the prep especially. Without it, you are going to be
> unhappy.
I don't like rebar in such a thin slab, or in driveways at all for that
matter. A thicker slab and no rebar is better than a thinner slab with
rebar. As RA opined, the prep work is where corners would be cut and
what would cause the driveway to fail.
I'd be nervous with a price that low. You need some additional bids.
R
Bob Morrison
> I don't like rebar in such a thin slab, or in driveways at all for that
> matter. A thicker slab and no rebar is better than a thinner slab with
> rebar. As RA opined, the prep work is where corners would be cut and
> what would cause the driveway to fail.
>
I concur with Rico's statement. A thicker unreinforced slab on a properly
prepared base will give you better service in the long run.
--
Bob Morrison, PE, SE
R L Morrison Engineering Co
Structural & Civil Engineering
Poulsbo WA
bob at rlmorrisonengr dot com
Bobk207
I'd say it was a bid from someone who really wanted the job & was
proabably going to skimp on the details.
I would suggest writing up (or obtaining) at least some sort of simple
specification for the prep, base, rebar (size & placement) & concrete
(w/c ratio, strength) . Also some words about the finishing & quality
of the result.
IMO 4" is was too thin & I'm not a huge fan of unreinforced thicker
slabs.
I would go with #5" min with #4 @ 18" both ways ......I hate jagged,
uneven cracked slabs.
I like them to crack in the control cuts :)
I'll probably catch some flak from the guys who don't like rebar in
thin slabs (they insist it does no good)
My experience is that it holds the pieces together
You're getting ready to spend a fair chunk of $'s.........how do you
want the result to look in a few years?
cheers
Bob
RicodJour
>
> I'd say it was a bid from someone who really wanted the job & was
> proabably going to skimp on the details.
>
> I would suggest writing up (or obtaining) at least some sort of simple
> specification for the prep, base, rebar (size & placement) & concrete
> (w/c ratio, strength) . Also some words about the finishing & quality
> of the result.
>
> IMO 4" is was too thin & I'm not a huge fan of unreinforced thicker
> slabs.
>
> I would go with #5" min with #4 @ 18" both ways ......I hate jagged,
> uneven cracked slabs.
>
> I like them to crack in the control cuts :)
>
> I'll probably catch some flak from the guys who don't like rebar in
> thin slabs (they insist it does no good)
>
> My experience is that it holds the pieces together
>
>
> You're getting ready to spend a fair chunk of $'s.........how do you
> want the result to look in a few years?
3" is the current accepted minimum for concrete cover over/under rebar,
right? That's a 6.5" slab. You're really good at spending this guy's
money! ;)
I'm curious why he needs a 14' wide driveway. Maybe so two cars can
pass? I'd go with a narrower driveway for the bulk of it and a couple
bump outs* to allow passing. It'd be a lot cheaper.
R
* I got a laugh out of that one. Firefox's spell checker flagged
bumpouts as incorrect, and gave me the choice of bump outs or bum
pouts. Bum pouts?! Has anyone in the history of the English language
ever combined bum and pouts??? Methinks not.
carolyn
Can you tell us why you don't like rebar in a thin slab? My understanding
is that concrete has great compression strength, but snaps easily when
pulled apart. The weight of a car on the top of a slab pushes down on the
top of the slab, applying compression strength to the top, while the bottom
of the pad is being pulled apart. Enough weight, and the cracks form in
the bottom of the pad and tear through the top. Put the rebar in the lower
half of the slab, and it will hold the bottom together and prevent that
tear through.
I don't know how think it needs to be for what weights, and 5" may be enough
for cars, but what about the 18 wheeler delivery truck, dropping off a new
table saw? (Yeah, my saw and drill press were delivered in an 18 wheeler.
5" and rebar may be over minimum code for a driveway - but the worst that
will happen is that it will be too strong and last much longer than it
otherwise would.
Carolyn
> I'd be nervous with a price that low. You need some additional bids.
Additional bids, and detailed bids, including the subbed. (I think that is
the term.)
Carolyn
--
Carolyn Marenger
DanG
cross cuts every 7 to 10 feet. There will be a lot of lineal
expansion in 310', I would use expansion every 60'. The rebar is
OK, but 4" is minimal. There should be a minimum of 1 1/2" cover
on rebar, making 1/2" bar almost too big to cover with 4". Money
is better spent on subsoil preparation and drainage.
$3 would be low in central Oklahoma, but our stone is all
imported.
___________________________
Keep the whole world singing. . . .
DanG
"AndyS" <andys...@juno.com> wrote in message
news:1162504705.5...@k70g2000cwa.googlegroups.com...
Bobk207
I agree that 14' seemed a bit wide for a 300' driveway.....the house I
sold last year had a 15' driveway but it was only 65' long....more of
an extended parking area.
In this case maybe a narrower drive with "bum pouts" & an enlarged
parking area....the material saved could go thicken the slab
I believe that cover requirements (& have had success with) are 3" for
soil contact & 2" elsewhere. so that would be 5.5". Unless they've
changed?
Yeah, I'll admit I'm good at spending money BUT it all depends on what
the guy wants preformance wise. Is he going to be disappointed when
the slab cracks (not in the cuts) AND shifts levels? And he's got
cracked up mess
If not, go thin but otherwise the 5.5 to 6" ain't that much more
material cost over the suggested 5" min. The extra concrete & rebar
wiil add a few thousand $'s to the job & (IMO) greatly enhance the long
term performance of the slab.
Soil condtions & weather could have major effects on the slab (I don't
the local conditons in Eureka, TX) but in SoCal they're generally mild.
RIco did you get the post base photos, I sent last week?
cheers
Bob
Bob Morrison
> Can you tell us why you don't like rebar in a thin slab? My understanding
> is that concrete has great compression strength, but snaps easily when
> pulled apart. The weight of a car on the top of a slab pushes down on the
> top of the slab, applying compression strength to the top, while the bottom
> of the pad is being pulled apart. Enough weight, and the cracks form in
> the bottom of the pad and tear through the top. Put the rebar in the lower
> half of the slab, and it will hold the bottom together and prevent that
> tear through.
> I don't know how think it needs to be for what weights, and 5" may be enough
> for cars, but what about the 18 wheeler delivery truck, dropping off a new
> table saw? (Yeah, my saw and drill press were delivered in an 18 wheeler.
In theory this is true if your subgrade is so poor that it won't support the
weight of the vehicle above it. I can tell you that NOTHING will prevent
shrinkage cracks in a slab. If you get one truck a year then a 5-inch slab
on a good base will be fine. If you get one truck per month then up the
thickness to 6 inches. If you expect frequent heavy traffic then make the
slab thicker, but you can still leave the rebar out. Put the money into
proper subgrade preparation and into proper crack control joints.
> 5" and rebar may be over minimum code for a driveway - but the worst that
> will happen is that it will be too strong and last much longer than it
> otherwise would.
I regularly specify unreinforced slabs on grade. The American Concrete
Institute has a whole book on this subject. Most city streets and much of
the interstate highway system are unreinforced slabs on grade and are
usually between 8 and 10 inches thick. My favorite example is an 18-inch
unreinforced slab I specified for a log handling yard. It sits on a 24-
inch deep compacted gravel base, which makes the total pavement thickness
42 inches. That pavement is subject to 130,000 pound axle loads and except
for some surface scarring has held up very well.
Glenn
#4 rebar, 24" oc, 100% tied and on chairs
"Bob Morrison" <SpamF...@junk.com> wrote in message
news:MPG.1fb4ff68c...@news.west.earthlink.net
Bob Morrison
> I believe that cover requirements (& have had success with) are 3" for
> soil contact & 2" elsewhere. so that would be 5.5". Unless they've
> changed?
>
Bob:
A minor correction to your calculation:
3" clear for the soil + #4 each way (= 2*5/8 OD) + 2" clear from top
= 6-1/4". I would use a minimum slab thickness of 6-1/2"
And this assumes that no salt for de-icing is used on the driveway. If
salt is to be used, then the top cover should be increased to at least 3
inches and even that is going to rust eventually. So, if salt is to be
used then add the cost of epoxy coating the rebar to the cost of the
project.
Boy, talk about spending other people's money! We sure can add it up fast.
<grin>
HerHusband
>> pass? I'd go with a narrower driveway for the bulk of it and a couple
>> bump outs* to allow passing. It'd be a lot cheaper.
Wide loads maybe?
Another option to cut costs, though it's a bit of an older look, would be
to pour "strips" on each side of the driveway. Maybe 2 feet wide on each
side. Vehicle tires usually don't run down the middle of the driveway, so
you could save money by not filling the center with concrete. Pour the
strips, and place gravel or grass in the center and on each side. You could
always upgrade later and fill the center areas with concrete as time and
money allows.
Just a thought...
Anthony
Bob Morrison
> I don't disagree with no steel but if it is for me, I still want
> #4 rebar, 24" oc, 100% tied and on chairs
>
Max code bar spacing is 18" o/c.
BTW, if you assume 3000 psi concrete, grade 40 bars and a span of 12",
this slab will support a wheel design load of 4000 pounds. Doesn't sound
to me like the rebar is worth the effort for such a thin slab unless you
want to simply pour the concrete on unprepared rough ground. And, as I
mentioned in another post you need at least 6-1/2" of concrete to meet
minimum cover requirements.
Bob Morrison
> Another option to cut costs, though it's a bit of an older look, would be
> to pour "strips" on each side of the driveway. Maybe 2 feet wide on each
> side. Vehicle tires usually don't run down the middle of the driveway, so
> you could save money by not filling the center with concrete. Pour the
> strips, and place gravel or grass in the center and on each side. You could
> always upgrade later and fill the center areas with concrete as time and
> money allows.
>
> Just a thought...
>
Anthony:
Good suggestion!
Glenn
patched up mess. If you can't do it right, I suggest you just put
down some gravel until you can do it right.
BTW, all driveways around here are 4" thick including mine and
though it be 30 years old, is not broken up. #4 rebar 24" ew oc
chaired on pour. Matter of fact, you won't find a crack in it.
KC area.
"HerHusband" <unk...@unknown.com> wrote in message
news:Xns98705796B...@216.196.97.136
RicodJour
>
>
> RIco did you get the post base photos, I sent last week?
No, Bob. I did delete my spam folder contents - I have my spam setting
on Kill instead of Stun - but I reviewed it before deletion. Maybe I
missed it. Please send it again. Thanks.
R
RicodJour
> In a previous post HerHusband wrote...
> > Another option to cut costs, though it's a bit of an older look, would be
> > to pour "strips" on each side of the driveway. Maybe 2 feet wide on each
> > side. Vehicle tires usually don't run down the middle of the driveway, so
> > you could save money by not filling the center with concrete. Pour the
> > strips, and place gravel or grass in the center and on each side. You could
> > always upgrade later and fill the center areas with concrete as time and
> > money allows.
> >
> > Just a thought...
> >
>
> Anthony:
>
> Good suggestion!
What the hell are you saying, Bob?! Anthony _sucks_ at spending other
people's money. We're going to have to get the smoking jacket back and
change the secret handshake again... ;)
When I lived in New Orleans about ten years ago, they upgraded
Tchoupitoulas. Major truck route following the river. Obviously they
have problems being on silty sand with an extremely high water table,
so they couldn't prepare a BMOC (Bob Morrison Official Compacted) base.
They designed the concrete road bed as a beam. The amount of concrete
and rebar in that slab was astounding. I'd tease the guys working by
pointing out that retaining walls were supposed to be _vertical_.
R
Matt Whiting
> In a previous post Glenn wrote...
>
>>I don't disagree with no steel but if it is for me, I still want
>>#4 rebar, 24" oc, 100% tied and on chairs
>>
>
>
> Max code bar spacing is 18" o/c.
>
> BTW, if you assume 3000 psi concrete, grade 40 bars and a span of 12",
> this slab will support a wheel design load of 4000 pounds. Doesn't sound
> to me like the rebar is worth the effort for such a thin slab unless you
> want to simply pour the concrete on unprepared rough ground. And, as I
> mentioned in another post you need at least 6-1/2" of concrete to meet
> minimum cover requirements.
>
Bob, what is the design wheel load if there is no rebar in a slab of the
same thickness?
Matt
Bob Morrison
> Bob, what is the design wheel load if there is no rebar in a slab of the
> same thickness?
>
Using a modulus of rupture (bending stress) for concrete of 2*SQRT(f'c)
and f'c=3000 psi, a span of 12" and an slab thickness of 5"
M = PL/4 = Fb * Sx = 2*SQRT(3000)*[(12)(5^2)/6] = 5500 #-in
For L = 12" P = 1835# or about one light pickup truck wheel load
If you increase the slab to 6-1/2" then P = 3100#
Compare the unreinforced slab to the 6-1/2" slab with #4 @ 18" o/c, which
gave a P = 4000#
If you increase the concrete strength to 4000 psi, then
P = 3100# * SQRT(4000/3000) = 3600#
Pretty simple calculation isn't it?
Of course it can be made more complex if you factor in the footprint of
the tire. Using this sort of uniform load (32-35 psi depending on tire
pressure) will either increase the design span or the allowable wheel
load. This sort of calculation is not solvable by normal algebraic
manipulation because there are too many unknowns and only a limited number
of equations.
carolyn
I would definitely include the subgrade and crack control joints. Except
maybe for a home made concrete patio stone. :)
>> 5" and rebar may be over minimum code for a driveway - but the worst that
>> will happen is that it will be too strong and last much longer than it
>> otherwise would.
>
> I regularly specify unreinforced slabs on grade. The American Concrete
> Institute has a whole book on this subject. Most city streets and much of
> the interstate highway system are unreinforced slabs on grade and are
> usually between 8 and 10 inches thick. My favorite example is an 18-inch
> unreinforced slab I specified for a log handling yard. It sits on a 24-
> inch deep compacted gravel base, which makes the total pavement thickness
> 42 inches. That pavement is subject to 130,000 pound axle loads and except
> for some surface scarring has held up very well.
Thanks for the information. I appreciate the knowledge.
Carolyn
--
Carolyn Marenger
HerHusband
> Anthony _sucks_ at spending other people's money.
:) OK, well how about a 6" compacted gravel base, and a layer of concrete
pavers? That's bound to cost more than just concreting the whole drive? It
would look nice too...
Anthony
RicodJour
Better. If you'd said a compacted base, concrete slab on top, some
tumbled travertine pavers, and radiant snowmelting (bonus points if the
driveway is in Florida) I'd forgive you and email you the new secret
handshake instructions. It's a wee bit more complicated than the one
you knew. It'll help if you're double-jointed. Take some pain meds
while you're learning it. ;)
R
Matt Whiting
> In a previous post Matt Whiting wrote...
>
>>Bob, what is the design wheel load if there is no rebar in a slab of the
>>same thickness?
>>
>
>
> Using a modulus of rupture (bending stress) for concrete of 2*SQRT(f'c)
> and f'c=3000 psi, a span of 12" and an slab thickness of 5"
>
> M = PL/4 = Fb * Sx = 2*SQRT(3000)*[(12)(5^2)/6] = 5500 #-in
>
> For L = 12" P = 1835# or about one light pickup truck wheel load
>
> If you increase the slab to 6-1/2" then P = 3100#
>
> Compare the unreinforced slab to the 6-1/2" slab with #4 @ 18" o/c, which
> gave a P = 4000#
>
> If you increase the concrete strength to 4000 psi, then
> P = 3100# * SQRT(4000/3000) = 3600#
>
> Pretty simple calculation isn't it?
Yes, but I'm still surprised the rebar adds so little additional
strength. I guess being nearly on the neutral axis is probably the killer.
Matt
RicodJour
>
> Yes, but I'm still surprised the rebar adds so little additional
> strength. I guess being nearly on the neutral axis is probably the killer.
That's the whole point about rebar in driveway and other slabs. People
view rebar as a panacea - that it's a simple way to make a slab far
stronger, and it's not. At least not the way it's usually done, and
not the way it can be done in thin slabs on grade.
R
Jonny
Central Texas. Non union laborers. Suspect some were not documented
non-native American workers. Small commercial company that normally does
roadwork and such for commercial parking lots and slabs, and county
roadwork.
Driveway is same 14' wide. 159' long. Also included adding a graduated
entry from garage doorway tied to garage slab, personnel entry door landing
tied to garage slab, a small sidewalk from that to the driveway some 10'
long. 3/8 rebar every 12". No chairs. Beams on edge were 12" thick. 7"
thick remainder. 3" of roadbase over stable Texas Hill country soil
(gravel/rock/gray clay). Full apron at street tie-in. Apron drainage
horizontally aligned with road frontage drainage, no culvert. Expansion
joints every 10' made from #1 cedar 1X4s. All boundary edges were rounded.
Included all flatwork. Surface is provided with purposely placed lines
across the driveway for traction and drainage. Natural water course is
across the driveway. Cost was a hair over 5K. The driveway was meant a
roadway to the garage, not the house.
The remainder of driveway is strictly compacted roadbase, which forms a
circle in front of the house. The center of the circle contains the septic
tank. The septic boundary is in large rock surface man-made (me) formation.
My sons compacted the roadbase with their loaded pickup trucks while it was
wet last summer. Had to wet it down twice. They went over the course for
over and hour. Had to get another load of roadbase as they mashed it down
so well the first time. 3" PVC-UV under one area 5' from concrete driveway
edge termination to allow drainage under straight roadbase area. Bermuda
grass seems to like the roadbase, weeds don't. I'll get over it.
--
Jonny
HerHusband
> That's the whole point about rebar in driveway and other slabs.
> People view rebar as a panacea - that it's a simple way to make a slab
> far stronger, and it's not.
I'm no engineer, but wouldn't the rebar help control cracking and just hold
things together when it does crack?
I'm probably wrong, but I would think the slab could settle unevenly if it
cracked without the rebar, whereas it might stay a little more stable with
the rebar?
In any case, rebar is cheap, so I've always added a couple of bars in the
sidewalks and stuff we've poured. It usually only added an extra $10 or so
to the total cost, so why not?
Anthony
Bobk207
I agree with you about rebar holding things together when it does
crack but this drivway is pretty big
If it has rebar @ 18" oc (both ways) we're talking about 6000 ft of
rebar....... so buying & placing the stuff would take some $'s.
IMO worth it, but others disagree
cheers
Bob
butwhat
I'm also curious as to what effect a driveway mat under the concrete
would have.
A friend of mine uses them to drive semis over.
He swears by the road mats.
I usually try to put down 12" of clean rock covered with visqueen for a
drainage base.
Bob Morrison
> strength. I guess being nearly on the neutral axis is probably the killer.
>
You got it. The effective "d" for a 6-1/2 inch slab on grade is only
3-1/4". Not to mention that #4 @ 18" o/c is a pretty small amount of
steel.
Bob Morrison
> things together when it does crack?
>
> I'm probably wrong, but I would think the slab could settle unevenly if it
> cracked without the rebar, whereas it might stay a little more stable with
> the rebar?
>
Anthony:
Yes the rebar does hold things together when they crack (and it will
crack). However, if there is no where for the slab to deflect then the
cracked sections will stay together just fine.
However, the point of proper subgrade preparation is to prevent
differential settlement by making the base consistent so the slab does not
have to span any distance.
As I said before I regularly specify unreinforced slabs: no rebar, no
welded wire fabric, no fibermesh, just plain concrete. These slabs
perform just fine if the contractor takes the time to properly prepare the
gravel base and subgrade. And as for gravel base I specify 3/4" minus
compacted crushed rock, not pea gravel.
Elevated slabs are another matter and are not what is being discussed
here.
Bob Morrison
12" of rock is a pretty substantial base. Unless you are on very soft
ground I think you could eliminate any visqueen or geotextile fabric and
still get excellent slab performance.
Remember that no matter what you do the slab will crack. so, put in crack
control joints. At least then it will crack in a straight line.
Bobk207
Bob Morrison wrote:
> In a previous post butwhat wrote...
> > I put rebar in everything. Did anybody recommend a mix?
> > I'm also curious as to what effect a driveway mat under the concrete
> > would have.
> > A friend of mine uses them to drive semis over.
> > He swears by the road mats.
> > I usually try to put down 12" of clean rock covered with visqueen for a
> > drainage base.
> >
>
> 12" of rock is a pretty substantial base. Unless you are on very soft
> ground I think you could eliminate any visqueen or geotextile fabric and
> still get excellent slab performance.
>
> Remember that no matter what you do the slab will crack. so, put in crack
> control joints. At least then it will crack in a straight line.
>
>
Bob-
For the 14' driveway under discussion, if you spe'd 5" unreinforced....
what spacing would you spec for crack control joints?
Would you go the full 14' width with no joint? A spacing of 7'
(across th4e width) is kinda short but 14' seems a little far.,
cheers
Bob
Bobk207
Bob Morrison wrote:
> In a previous post Matt Whiting wrote...
> > Yes, but I'm still surprised the rebar adds so little additional
> > strength. I guess being nearly on the neutral axis is probably the killer.
> >
>
> You got it. The effective "d" for a 6-1/2 inch slab on grade is only
> 3-1/4". Not to mention that #4 @ 18" o/c is a pretty small amount of
> steel.
>
> --
> Bob Morrison, PE, SE
Bob-
Agreed the "d" is really small but i think other factors are at work &
the rebar wards them off......kinda like a rabbit's foot. :)
cheers
Bob
Bob Morrison
> what spacing would you spec for crack control joints?
>
> Would you go the full 14' width with no joint? A spacing of 7'
> (across th4e width) is kinda short but 14' seems a little far.,
>
My spec for crack control joints reads:
Crack control at max 150 sq ft and max aspect ratio of 1.5:1
So, a joint pattern of 10x14 (140 SF) with an aspect ratio of 1.4 fits
within the parameters. You could probably get away with 12x14, but that
may be pushing it a bit. This is one of those things where more is better.
The joint is a 1" min deep sawcut or tooled joint. Some people like to use
vinyl strips, but it is hard to get them straight. Sawing of joints should
be done as soon as the slab is hard enough to walk on with out leaving a
mark. The new lightweight joint saws are waterless and look something like
a gas powered lawn edger.