Looking to do a small pour to replace a driveway apron to a commercial establishment. 8″ thick apron and associated sidewalk.
I am contemplating the use of a commercial grade fiber additive tot he concrete instead of wire mesh.
Any feedback, pros or cons?
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Replies
Code here accepts it as equivalent. I'd go with both, if it was my house.
"...craftsmanship is first & foremost an expression of the human spirit." - P. Korn
CaliforniaRemodelingContractor.com
Try this Pete.
http://www.answers.com/topic/reinforced-concrete
Fiber mix in concrete slab will reduce shrink cracking, but will do very little for axial forces applied to the concrete. WWM placed in the slab is mostly there to hold concrete together after it cracks. For a slab that will be loaded either continuously or intermittently, like a drive way, rebar is the the reinforcement to use.
For an 8" thick driveway pour I would consider the rebar because the thickness alone indicates a higher expected loading than a 4" residential slab. I have poured 8" slabs for loading dock aprons and driveways to warehouses. We used a 2x2' grid of #4 rebar in the lower half of the slab and appropriate control joints.
As important as the reinforcing is, the sub slab preparation is even greater. A well compacted (standard proctor) is the minimum with a 4" crushed stone base. For higher traffic and loading areas we have had to achieve modified proctor of 92 to 95+% and the crushed stone.
Not knowing what your commercial application is, the first question you should ask is what the driveway is used for and what compaction is needed. Then decide on your slab reinforcement.
I am contemplating the use of a commercial grade fiber additive tot he concrete instead of wire mesh.
They are NOT equivalent. Fiber mesh limits microcracking - essentially makes it easier to get a better cure. Wire mesh limits movement for larger cracks.
You really need BOTH to do a good job.
but wire mesh is always on the bottom so fiber does a better job
what if the wire was pulled to the middle during the pour? Still the same?
If you are going to use WWM the best aproach is to use matts, not rolls, and tie it to chairs, lots of chairs. Then at least it starts off where you want it and may even manage to stay there if the pouring crew doesn't manage to walk it down.
If you are going to use WWM the best aproach is to use matts, not rolls, and tie it to chairs, lots of chairs.
That's certainly one way to do it, and it will work fine.
We find it easier, though, to place 2" of concrete, lay the mesh on that, and then fill the forms. You would think that walking on it would push it down, but when you do it this way, it doesn't.
This way works great - and I learned it from an FHB book :-)
How do you tie the rolled out wwm together durring a pour, or for that matter, matts if you use them?
I know you walk the mesh down if you have a 2" layer of concrete (wet) inder it, but that seems like additional work to pour 2", place wwm, then go back over with another layer of 2-4" on concrete.
We did some large warehouse loading dock aprons and drives. A 50 to 100 yd. pour was not unssual. I wanted everything in place before the pumper truck and first ready-mix truck arrived. Once the show started, everyone had to know thier role and get-r-done right the first time. In order to do that, you need to follow brownbags unspoken rule "make it idiot proof". The labor pool for a lot of concrete work seems to come from the lower end of the gene pool sometimes.
:~)
but wire mesh is always on the bottom so fiber does a better job
Wire mesh should never be on the bottom, it should be installed in the middle of the slab.
Mesh does not do the same job as fiber, so fiber alone cannot do a better job - it does a different job.
The only "right" solution is to use both and install them properly.
Here's my 2 cents. Listen to Dave. He knows what he is talking about.
Is the apron into a garage or a building? Is it an approach from a street into a parking area? What will be rolling over it? Cars, small trucks, medium size trucks, concrete trucks or what?
It makes a difference. Fiber additives is not structural reinforcing. More like cosmetic.
Locally for approaches, out city requires 6" 3000 psi concrete, #4 rebar 12' o.c. both ways on chairs, doweled into existing/abutting paving and over min. 6"compacted base.
I would typically use steel mesh. I keep hearing how great this fiber is though although I suspect it is mostly because of how much easier it is.I think I might go ahead and use both in this case.The apron is for a driveway into a fast-food parking lot. There will be everything from cars to delivery and garbage trucks on a regular basis.
<!----><!----><!---->
I refuse to accept that there are limitations to what we can accomplish. Pete Draganic
Take life as a test and shoot for a better score each day. Matt Garcia
I have stop specing wwf on my jobs, I think the fiber is superier to wwf and have the track history to prove it.
even after a crack has formed? I would think that this would be where the wire mesh would show it's attributes best by keeping things together.
<!----><!----><!---->
I refuse to accept that there are limitations to what we can accomplish. Pete Draganic
Take life as a test and shoot for a better score each day. Matt Garcia
The apron is for a driveway into a fast-food parking lot. There will be everything from cars to delivery and garbage trucks on a regular basis.
Use rebar, not mesh - you need the structural reinforcement for that type of application.
I am not sure I can buy that rebar will improve the strength of 8" thick concrete.I can see fiber doing that but the rebar would only come into play if a complete fracture occured... no?-->-->-->
I refuse to accept that there are limitations to what we can accomplish. Pete Draganic
Take life as a test and shoot for a better score each day. Matt Garcia
Edited 4/23/2009 8:05 pm ET by PeteDraganic
I am not sure I can buy that rebar will improve the strength of 8" thick concrete.
The primary purpose of the rebar is to hold the pieces together when the concrete cracks. With a slab with that kind of usage, the traffic will quickly break wire mesh when the cracks occur, due to differential movement.
ok, i am with you now.
<!----><!----><!---->
I refuse to accept that there are limitations to what we can accomplish. Pete Draganic
Take life as a test and shoot for a better score each day. Matt Garcia
I use rebar in my slabs on the understanding that it will prevent cracks rather than hold things together once they happen. But who knows. Once you go to rebar rather than mesh, what is your feeling about placement? Still at mid-slab?
The best method of preventing cracks is breaking up the size of the slab by saw cuts or other control joints. The smaller the better. Rebar + control joints = happiness.
I use rebar in my slabs on the understanding that it will prevent cracks rather than hold things together once they happen. But who knows. Once you go to rebar rather than mesh, what is your feeling about placement? Still at mid-slab?
If the substrate fails or "dips" in places, rebar will help prevent cracking and provide some structural strength.
Regarding placement, on thin (e.g. 4") slabs it pretty much has to be in the middle to get the coverage needed.
not one note here had any accuracy at all, you can tell nobody here know anything about concrete, so here the 411.rebar and fiber/mesh do not do the same job, they are design for two different application.Fiber and mesh are basically the same idea but two different methods. they are design to hold the concrete together till the intinal cure. They are not reinforcement materials. The fiber is better because it hold million more point all through the concrete through the whole thickness. so the shrinkage cracks are held. welded wire mess has the same application but it is never installed right, never. even if held on chairs it only holds the are a that its place. Not under it or above it. cracks still happen. wwm will only whole the curing cycle cracks. It is not reinforcement. It does not replace rebar, never will. neither does fiber.rebar is for load factors. it does nothing till a load is applied. as concrete sits unloaded nothing happen, when a vehicle or load is applied, the concrete slab will try to bend. rebar bend but not in tension. the reaction of the rebar will hold the concrete from bending. if bending occur, the crack starts.if the concrete itself is stronger enough to hold the load, no rebar is needed.cracking occur through bending and shrinkage. rebar is used for load factors. fiber and welded wire for shrinkage. fiber is stupid proof. welded wire is wasted material and dangerous to install. no clean up with fiber, wire you have to cut, install, pull and pick up the piecs left over, and the half of a roll that you paid for and much haul to the lay down yard.the wire and fiber does nothing for the strength of the concrete.
So the rest of us are all meatheads?
I won't address that question but I will say that brownie is correct in all he said.
They can't get your Goat if you don't tell them where it is hidden.
When my ex-navy electrician felt I was being a bit too lippy he used to say "I guess you haven't been told today" :)
I can't tell if he was right or wrong. His explanation of how rebar works read like a blind man describing how to make pizza.
Edited 4/24/2009 1:00 am ET by fingersandtoes
I will give it a shot. Concrete is great compressive material.
Concrete is absolutely horrible in tension. When , not if a void ( or water saturates the soil to the point of plasticity) develops beneath the crete the bottom 1/2 of the crete is now in tension, crete is lousy and failure prone in tension. Steel (re-bar , not WWM !!) on the other hand is very strong in tension so by using correctly placed steel (there have been volumes written on that subject for the engineers and there is much available by googling the subject) You give the concrete the strength to resist the tension ( bending) load applied to it because the steel prevents the crete from bending. dovetail trying his hand at channeling brownie.
They can't get your Goat if you don't tell them where it is hidden.
Steel (re-bar , not WWM !!) on the other hand is very strong in tension so by using correctly placed steel (there have been volumes written on that subject for the engineers and there is much available by googling the subject) You give the concrete the strength to resist the tension ( bending) load applied to it because the steel prevents the crete from bending.
That I agree with, since it is what I was trying to say earlier, just explained more fully.
The exception would be the WWM does provide more tensional reinforcement than one might expect. In many cases, it may provide enough, but it takes a LOT of mesh (not just one layer) to match the strength of rebar. The one advantage of mesh over rebar is that the mesh has the cross wires that give it better pull-out resistance - until the bonds break. You can accomplish the same thing, but better, by welding rebar in a grid.
that is correct
What you describe is accurate for suspended slabs. Oversimplifying slightly, they act like any beam. The top experiences compression and the bottom tension. That's why as you point out it is important that the reinforcing be near the bottom where it can resist the tension.
A slab on the ground experiences loading from above from traffic and from below where differential settlement of its base occurs. So how does rebar in the middle of a 4 or 6" slab, that is to say on the neutral axis which is neither in tension or compression, resist these forces?
I'm not sure any of us have a good handle on what happens in these slabs. Instead we have experience in what has worked and in the absence of a more convincing explanation, I'm as likely to go with some of the other suggestions as Brownbags.
I didn't comment on the reinforcing being in the middle of the slab because that location is not what I have been taught. I was taught it belongs in the bottom 1/3 of the slab, and most often the engineers I have worked with show it that way , or give a specific dimension for it to be at.Edit for correction.
Edited 4/24/2009 1:20 pm by dovetail97128
"A slab on the ground experiences loading from above from traffic and from below where differential settlement of its base occurs. So how does rebar in the middle of a 4 or 6" slab, that is to say on the neutral axis which is neither in tension or compression, resist these forces?"
That's a good point. The answer is that rebar needs to be embedded a certain amount (usually min. 1 1/2") for it to have any bite at all. So, if you have a 4-6" slab, but put it anywhere except near the middle (especially if the base isn't perfectly flat, or the rebar is bent, which it always is), the concrete around the knurls may shatter off as the tension load is applied.
You are correct that it is in the neutral axis of the 4-6". It is actually acting in that case like the 'extreme fiber' of each half, above and below. 2-3" of concrete acting completeley in compression is plenty strong.
As some have noted, a slab on grade may bend like a smiley face, but may also bend like a frown. The middle placement works equally well for positive moment and negative moment.
If you do know exactly where your loads are applied, then you can worry about top or bottom of beam placement. For instance, elevated roadways usually have the majority of their steel at the bottom of the slab in the middle of the span, but the opposite placement over the tower supports.
k
Edited 4/24/2009 2:47 pm by KFC
Finally, a clear AND accurate answer!
Of course, it has nothing to do with the op's question! typical me...
k
Thank you for the explanation.Want to tackle correct placement in restrained and unrestrained retaining walls next?
Edited 4/24/2009 4:35 pm by dovetail97128
KFCExcellent post. Brownbagg knows his stuff, too, but his writing style loses some of the audience.Bill
Thanks Dovetail, Mike Maines and BillBrennen for the compliments.
Brownbagg knows a thousand times more than I do about concrete, I'm certain.
If I can help explain the concepts in simple terms, that's probably because my understanding is kind of simplistic. Kind of like how I'm good with kids, because I'm immature... lol.
k
Add me to your list of fans on this one for your clarity.
I don't disagree with anything Brownbag wrote ( I think...). It's not where we start from but our solution that differs.
I accept cracking and unanticipated loads as inevitable. By using a combination of control joints and rebar you get to decide where the cracks occur, but still have a slab that acts on some ways monolithically because it is held together by steel. Sort of like a series of concrete rafts linked together. This works over time because it is able to adapt to changing conditions such as the erosion of the substrate, or roots pushing upwards. I am using rebar as "extreme fibre" as you put it, not in the sense Brownbag saw it being structural. That's just my meathead solution.
Well, the extreme fiber is a structural term, so I'm not sure what you mean. I hope I didn't muddy the waters by using the term fiber...
I was just pointing out that you were correct that the rebar in the middle of a 6" beam isn't in tension or compression when you look at it as a 6" beam. What you have then is effectively a 3" beam with rebar on the top, and a 3" beam with rebar on the bottom.
But maybe I missed your point...
k
Edited 4/24/2009 8:13 pm by KFC
"I hope I didn't muddy the waters by using the term fiber..."
Not at all. I see rebar in these slabs as "big mesh", as opposed to structural steel placed to resist specific predicted loads. That's all.
""I see rebar in these slabs as "big mesh", as opposed to structural steel placed to resist specific predicted loads. That's all."" And therein lies the problem I believe. In some cases you may well be correct , that all the bar is is big mesh.
In other cases however you would be wrong and the bar is there to do exactly what you say, be structural steel to resist specific loads. So for those who are offering advice( myself included) how can we know which is the case?
Well in this case in this thread we are discussing a drive way approach. That to me means heavy loading by vehicles, which means bar in the bottom third.
Now my assumption can easily be proved incorrect , all one has to do is point out that the adjacent soils are heavy clay and prone to swelling and the engineering of the slab then needs to change. I asked a question a few posts back about reinforcement in retaining walls exactly for this reason.
Conventional wisdom around here is the bar should be within 2-3" the earth face of the wall because that is the tension side . Virtually every concrete contractor I have dealt with will tell you that. That is generally accurate for an unrestrained retaining wall (Top of wall has nothing holding it in place so it can move) , but tie the top of the wall to a "drag slab" above it and you change the loading on the wall and the exposed face of the wall becomes the tension side of the wall as opposed to the compression side.
If you followed conventional wisdom in placing the bar near the earth side the bar would be of no help as it is in compression and the wall would be prone to cracking in the middle as a result. Some days them dang engineers actually earn my respect and their money!
They can't get your Goat if you don't tell them where it is hidden.
"Some days them dang engineers actually earn my respect and their money!"
And other days? He he.
Oh there have been other days when I wondered ... Like the time one of them had 2-1/2 bolts holding a 30' long I beam to a column . Bolts were in shear , beam was holding up a slab under a winery crush pad, fully loaded 2 ton trucks delivering fruit onto that slab, plus a fork lift and all the crush pad equipment. Believe it or not a laborer caught the error and brought to his foremans attention who brought it to mine.
Engineer was grateful enough he asked for the laborers address , wanted to send him a bonus.
They can't get your Goat if you don't tell them where it is hidden.
My doubts about engineers stem entirely from their behavoiur at Christmas parties :)
They really lose credibility in a nudie bar.
To answer the OP's question, I would put in #4 bars at 12-inch both ways, at mid slab. When I design commercial driveways, I specify the #4 bar, with chairs at 24-inches,because it will stay close to where I want it, the middle of the slab. I have done quite a bit of demolition work on driveways, and other slabs on grade, as well as some forensics engineering on failing slabs on grade. In nearly every instance, the welded wire mesh (WWM), had been trampled into the bottom of the slab, or even into the base gravels during placement. WWM might work, if half the depth of concrete were placed, the WWM laid on top of it, and then the top placed using a rolo-screed or something similar to prevent any forces that would push the WWM out the bottom. I have examined a lot of demolished slabs. And, used rebar depth indicators, and cores to examine failing slabs. I have never found WWM anywhere but the very bottom of the slab, where it is of very little value. Fiber was initially marketed as a solution to shrinkage cracking. Testing and experience since has indicated that it does add to the flexural strength of concrete. However, it should not be considered as a replacement for reinforcing steel. In a slab on grade, the reinforcing steel is placed at mid depth because the loading is nearly always, a point load, but you don't know whether it will be from the top, or bottom. With the reinforcing steel at mid slab it's position is the best location to resist the tensions placed on the slab form both directions, as it tries to bend. Now to address some of the other things that popped up in this thread:Reinforcing steel does not need to be embedded 1.5-inches from the surface to develop strength. The depth of embedment for strength is a function of the compressive strength of the concrete. Reinforcing steel is typically embedded a minimum of 1.5-inches to resist corrosion. When water passes through the 1.5-inches of concrete, the pH is increased to at least 11. Steel in an environment with a pH greater than 10.5, does not form the common red flaky rust, but forms a black hard oxide similar to Parkerizing, seen on military weapons. If you break apart reinforced concrete as part of a demolition job, look at the steel that is exposed. It has a deep dark surface, similar to a Parkerized or blued rifle. If you want to see how effective concrete is at raising the pH, and preventing corrosion, get a couple of glass jars, and put a short piece of reinforcing steel, in each one. Add a small piece of concrete to one of them. Then fill them both with tap water, and screw on the lids. Within hours you should begin to see the difference. Eventually the rebar in the jar without the concrete will rust away, leaving only red rust flakes. The rebar with the concrete, will turn black, and still be in very good condition even decades later. Tensile reinforcement in a retaining wall belongs on the soil side of the wall. If you picture the wall and footing as two separate plates held together by the steel, with the outer bottom of the wall as the hinge: then the soil pressure is acting to push the wall over by rotating it around that hinge, and placing the steel as close to the soil side of the wall as possible, gives the steel the most leverage to resist the turning. I hope this explains things. I'm trying to do this with out any math, so I'm never quite sure of how clearly it comes across.
I basically agree with everything you said, except when you said that rebar doesn't need to be substantially embedded to resist tension forces.
If corrosion is ignored as a factor, what would you say is the minimum embedment rebar needs to adequately grab concrete to resist tension loads in a slab? Just skinned over? What size aggregate are you assuming?
k
Edited 4/25/2009 12:33 am by KFC
Sorry I can't give you exact numbers. Haven't had to do anything close to serious thought on the matter in nearly twenty years.There is, (might be was) a discussion of it in the commentary side of ACI-318, and it does depend mostly on a the strength of the paste. The lower the water to cement ratio, the less coverage it takes.I remember sitting through a 75-minute lecture, on calculating the minimum embedment depth required to develop the load in the bars, complete with lots of equations on the board, which was terminated by the professor stating that none of it mattered. Because, the depth was always dominated by the desire to provide corrosion protection, and would always be given by the ACI-code, and would always be more than required to gain the strength. The relationship to embedment depth and aggregate size is driven by the desire to assure complete coverage of the bar, and the need for the mix to flow around the bars. Not normally an issue for residential, or light commercial, but more critical in bridge design where there there is frequently large quantities of reinforcing steel packed into the bottom of the member.
Yeah, that's what I was taught.
Which is why I threw 1 1/2" out as a structural need.
I figured someone would bring up the corrosion requirement, and tell me I'd confused the two. But I've yet to hear anyone ever actually quote a figure on the structural requirement for embedment alone, so until that happens I'm standing by my statement that the minimum corrosion requirement for embedment is also the minimum structural requirement for embedment, as a general rule.
But if someone's got the stats, by all means lay them on me.
k
Somewhere packed in a box, from the last move, I still have the notes from my concrete class. But, I have about thirty or forty boxes of books I still haven't unpacked. So, it will be a while. But like the Prof said; it's academic because the corrosion requirement will always be at least 1.5-inches.
I seem to recall it's 2 or 2-1/2 times the maximum aggregate size, the theory being that if a big piece of aggregate happens to be between the bar and the surface, you still want some cement and fine aggregate for cover as well. Microcracks can easily develop around larger chunks of aggregate. 3/4" is the most common large aggregate, so twice that = 1-1/2". But my concrete books are packed away too.
since you dont have your books around, clearance around rebar and formwork is 1 1/2 times the largest aggregate. I usually say if you can wrap your hand around the rebar and your knuckle doesnt touch nothing its good. we have a 3/4 max here on aggregate.
Edited 4/25/2009 11:27 pm by brownbagg
Thanks BB
Also to resist "Frost Pop" in cold climates.
Thanks, brownbagg.
k
True (as I understand it) for a free standing retaining wall.
Not true for a retaining wall that has the top restrained.
(Drag slab, shear diaphragm etc) If the Top is restrained then the bending force moves to the middle of the wall on the face opposite the earth side. The wall is no longer trying to tip and over turn , rather the forces are trying to break it as it were. Or at least that is what 3 engineers here that detailed bar location have explained to me.
I am not an engineer and try hard to understand what it is they are telling me and the "Why" of it all. Take a poured basement wall with a floor diaphragm at the top of the wall and a slab at the bottom, where would you place the bar in the wall?
They can't get your Goat if you don't tell them where it is hidden.
Not at all. I see rebar in these slabs as "big mesh", as opposed to structural steel placed to resist specific predicted loads. That's all.
In most slabs I actually see it as structurally resisting unspecific loads. That is, it might be positive or negative bending moment (smiley or frowny for the non-geeks), and it works equally well either way.
k
yes
the primary purpose for rebar is to add tensile strength.
Holding the slab together is a secondary function of the rebar.
Concrete is strong in compression, but weak in tensil strength.
Rebar adds the tensil stength. The use of rebar or WWM is depentent on the intended use of the slab and the loads it will carry. He could use road wire, 6/6x6/6 instead of the more common 6/6x10/10 used in light duty requirements like residential driveways.. Matts are the better way to go with the heavier guage WWM because it is easier and safer to handle than rolls.
"I am not sure I can buy that rebar will improve the strength of 8" thick concrete."
Do you use rebar in your footings, which are typically 8" thick?
When you get in commercial construction, it is not uncommon to see footings much thicker with reinforcing. A while back we managed a building that had footers that were 10'x10'x21", with 12 #5 bars running each way evenly spaced.
I'm pretty sure that rebar is supposed to stop the concrete from fracturing, not come into play after it's happened.
Jon Blakemore RappahannockINC.com Fredericksburg, VA
It seems like every time I comment here at BreakTime I say something stupid, but I'll try again.
Everything I've read says that rebar is used to improve the tensile/bending strength, not the compressive strength of concrete. So, if the base is "good enough" and all forces will be compressive, is rebar absolutely necessary as long as the conrete is thick enough?
I'm not an engineer and do not have extensive knowledge of concrete.However, I do know that the footing I described were "only" 21" thick with a 6" slab above. The column that sat on this footing was only 12"x12", so the load would need to travel at a 63° angle at the least to achieve the bearing capacity called for. My guess is that the engineer would have had to specify a much thicker footing if no reinforcing was to be used.This is exactly the same situation as Pete has, but there may be some parallels.
Jon Blakemore RappahannockINC.com Fredericksburg, VA
What you are saying is basiclly true. What happens is at some point the amount (thickness) of the concrete reaches a point of deminishing returns.
You can use a lot less concrete in conjunction with "properly designed" reinforced concrete beam, footing or slab thereby reducing the cost. Concrete only, does not flex very much before cracking. As mentioned before, a properly compacted base is also essential. It does'nt take much movement to crack it if it is not reinforced..
If someone is going drive a fully loaded concrete truck, for example, over my approach, I'm going to want some steel in it. If you can get the same or more strenght and for less money, why not do it.
Also, if you have expansive soils, (high clay content) you may have very high forces operating in the opposite (up) direction than that of loading (down).
For a section of I-95 in Maine, my dad did what Brownbagg does now, inspect the work to make sure it was done properly. Last week he was telling me that those concrete slabs, on extremely well prepared substrate, have NO reinforcement. None. And they are only 6" thick.
I was incredulous, but he said it's partly because the base was so good, and mostly because the concrete had an extremely low slump (1.5)--so stiff that if had to be mechanically placed. A big paving machine literally vibrated the concrete into place. After 35 years (placed the year I was born) of cold, salty winters it's just this year getting replaced. He's taught me a lot about concrete.
If all the forces were compressive, you wouldn't need rebar. But I'd be interested to know in what situation there are no reaction forces. When there's a load from above, the bottom is going to be in tension. You can get away with it in slabs if the base is good because the loads are so small.
In typical residential walls, you don't even need it in the footings in most cases IF you have bars top and bottom in the walls. The walls act like giant beams, spreading out the load. The footings are just there to create a level surface to form the walls.
"In typical residential walls, you don't even need it in the footings in most cases IF you have bars top and bottom in the walls. The walls act like giant beams, spreading out the load. The footings are just there to create a level surface to form the walls."
Here on the Island, where foundation walls are often only two or three feet tall, we use a variation on that. We form and pour the footings and wall at the same time. With the steel tying everything together you get a concrete beam with a large bottom flange which is more forgiving of voids or differing soils in the excavation.
That's right, Jim Blodgett had an article a while back about how to form what I guess you would call a monopour frost wall.
We occasionally do a thickened-edge slab, which is also a monopour, but it's critical to have rebar in the thickened edge to create what is essentially a grade beam tied to the slab.
I seem to upset people with my communcation skills, remember english is my second language. so in conclusion I was trying to state.fiber and wwf are not reinforcement of the sense of rebarrebar is reinforcement for load factorsfiber wwf is for curing shrinkage cracksI dont like wwf due to dangeous and that labor wont do their jobfiber is stupid proof, concrete finisher are well.........----------------------------------------------------------------
on the calulator rebar is not needed for most house footers but it does hold everything together nicelysteel is not cheapI like rebar
----------------------------------------------------------------I can and do place non cracking slabs, I can do it everytime if possible.a crack slab is a poor craftmanship of sombody that dont carecrack less slabs are not cheap
-----------------------------------------------------------------dont believe me on crack less slab, Ask Gabe
BB, I gotta ask... what is your first language?
<!----><!----><!---->
I refuse to accept that there are limitations to what we can accomplish. Pete Draganic
Take life as a test and shoot for a better score each day. Matt Garcia
BB, I don't think you upset anyone--it's a fairly complicated subject and you obviously know your stuff. It's taken 50-something posts just to tell Pete that yes, he should put some rebar in his slab!
I have done just enough concrete work to be dangerous.
The few times I have placed concrete with fiber I have had a difficult time getting a smooth finish. The fiber gets clumped up on top. Is this common?
It is one of the downsides to fiber. Also, if you have aggressive soil chemicals, it can function as an infiltration path, to let things like sulfites into the concrete and begin breaking it apart.
Thanks for the reply. And to you too Mmiikkee. I always learn something here.
you are starting to finish it too soon
no one hear has mentioned STRUX fibers yet. Conventional fibermesh is a micro fiber while STRUX is a macro fiber. Might want to consider it as well.
Sorry Brownbagg. I didn't know English was your second language. I thought you were just in a rush to set us straight.
Does your city not have a spec. for paving driveway approaches? It has been my experience that anytime your did anything on city, state or Fed. property (a right-of- way in this case), you will be required to set up the forms, place the steel and call for an inspection prior the placing the concrete.
You install an approach without a permit and an inspection around here and you just bought yourself some jackhammer time. It might be worth your while to make a call (anonymously)to your friendly AHJ just to be safe.
My concrete supplier advised me that fibers in concrete helps control hairline and spider webb cracking. It is not structural in the sense that rebar is. You don't see highways and runways not using steel reinforcing.
Your idea to do both is the best of both worlds. Good luck
already discussed this with the city (it is not the city where I live). There needs are minimal and code only requires 6 inches although the inspector and I agreed that 8 would be better. he asked if I would use wire or fiber to which I said wire. I asked him his thoughts on fiber and he said either would be fine. So here I am as a fiber virgin feeling out the situation.edit to add.... btw, I am not interested in minimum code. I am more interested in a durable project.-->-->-->
I refuse to accept that there are limitations to what we can accomplish. Pete Draganic
Take life as a test and shoot for a better score each day. Matt Garcia
Edited 4/24/2009 8:29 am ET by PeteDraganic
I drive a heavy 37' diesel pusher motorhome and park it next to my house.
The driveway is 6" thick with an extra turn down on the edge and the bus sits parked on two 3' wide ribbon strips that are 8" thick with 2 #5 rebar near the bottom. The steel is placed just like you would place it for a footing. I used 3500psi, 4 slump, no mesh and no wire.
This was poured last August. There are no cracks and no settling
FWIW
Also, especially at the roadway/driveway junction, thicken it up.
Sounds like your good to go.
I didn't mean to over advise. Often when one is not there and doesn't know exactly what the situation is, it's easy to start answering questions that weren't ask. Sorry.
If the inspector is happy. If your are happy. It's a good day..
For the slight price, use the fiber mesh, too.
I'd also recommend going with the highway mix I told you about in your other driveway thread. They can drive on it the next day!
"Preach the Gospel at all times; if necessary, use words." - St. Francis of Assisi
No, I didn't vote for him; but he IS my president. I pray for the his safety, and the safety of his family every day. And I pray that he makes wise decisions.
Edited 4/23/2009 9:32 pm ET by SteveInCleveland
Good thread.
Special thanks from me to brownbagg and Dovetail. I understand this better now.
Hey, Pete, would you take a few pics and post them, and maybe describe what you actually would up doing?
Sort of a BT "as built". < G >
I'd be glad to.... if I get the job, of course.
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I refuse to accept that there are limitations to what we can accomplish. Pete Draganic
Take life as a test and shoot for a better score each day. Matt Garcia