mesh or rebar in driveway?

GarageEnvy

I got a couple of bids on my driveway work and additional walks. I noticed that neither bid (both from highly reputable companies) did not include mesh or rebar. Apparently it is not typical but occassionally done in my area. Ironically both said some tract home builders spec it (to minimize lawsuit and complaints) but it's rarely done on custom homes. So I talked to them about it and here's their take. Mesh will help with smaller cracks but adds little structural reinforcement and costs about $.15 per sf extra. That's about $550 on my job and well worth it in my opinion. Now the step up is rebar and that's $.64 per sf plus because of the size of my job and the fact that they won't be able to back the truck over it I need 2 or 3 more pumps on site (already have 2 in the bid) at $350 per pump. Basically it is $2,100 more for the rebar and another $1,000 for the pumps. My area has no snow or frost issues and there won't be any heavy trucks on it. There are 2 large trees as you can see in the photo that have cracked the asphalt driveway. Both contractors confirmed what I was thinking in that neither mesh or rebar will stop tree root cracking. The red line shows where the new driveway will expand over into. The picture shows the old garage and the new one expands to the right. Also I will have two grass strips in the center of the circle drive.

So would you make the leap into rebar? Stick with mesh? or not even bother with either of them? Total bill for concrete is about $13,500 so for our family this is a huge investment.

LEVE · Sep 13, 2010 #2 Rebar... all the way...

Rebar... all the way...

ddawg16

Just how big is this driveway? More than one pump? Just how many guys is he going to put on site? One pump is one crew....two pumps is 2 crews....it would seem to me that they would be steping on each other.

But like Leve said....yes on the rebar....your driveway can get a lot of point loading...that is where the rebar comes in....the mesh is fine for things like walkways and patios....

I happened to sit next to a foundations engineer the other day on one of my plane trips and we got into a detailed discussion on concrete.

He also suggested using fibers if your concerned about cracks....

And last but not least...preperation....if you lifting up existing and putting down new...and the ground is not getting disturbed much....the soil should be fine....but if the soil has been worked and has not been given a lot of time to settle...it needs to be compacted....and it wouldn't hurt to put down a couple inches of sand/gravel.

The first time I did a stone patio....I didn't put down a bed of p-gravel....just and inch or so of sand....within 6 months I had issues with stones moving around and loosing the flatness.....next time around I put down 4" of gravel and 2" of sand.....after 3 years it looks like like the day I finished it....

Torque1st

Rebar gets my vote. Mesh is largely worthless. Unfortunately the concrete WILL crack where the rebar ends so design and locate your control joints appropriately. In my city they will not allow rebar in the approach section of the drive. The concrete cracked at the control joint within a few days of placement.

From the picture I do not understand the need for concrete pumps.

You may want to discuss the methods of placement and pumps needed. A good contractor can set up the rebar and move a section into position and tie it in minutes between truck deliveries. Use concrete bricks or broken concrete paver sections under the rebar instead of rebar chairs or regular clay bricks.

GarageEnvy · Sep 13, 2010

The picture might be a little deceiving because it shows the old house but originally it was one pump and crew for the side yard and rear walk. The second pump was for the front drive. According to the estimator the site is spread out enough and the drive is deep enough (65') to need additional pumps. They claim the chute would only reach 20' and there's no spot to back up without going over the rebar. In fairness this pump estimate was an "on the fly" deal when I inquired about using mesh or rebar. He did say he'd get back to me to see if they could trim the number of crews and/or pumps. He's saying that with a smooth finish it's a simple power trowel, like they did with the garage slab but now with a broom finish it's a little more hand work and they need additional crews. I forgot I had this picture from the estimator. It shows the job a little better.

I have to admit the pump deal surprised me too but even when they had the 1800 sf slab to pour and could back up to the edge (it is 34' deep though) they brought in their boom truck.

Torque1st

I can see the rear walk needing a pump if it was extensive. Otherwise a power buggy or a couple of wheelbarrows would work.

I recently had 1890 sf placed and it was 95' deep with no pump truck needed. They did use a ~15' chute extension. They did the deep section one day and came back for the 24x55' section, porch and sidewalk the next day.

twostory · Sep 13, 2010

I did a 1,800 sqft driveway replacement last year. 5 inch thickness, 4,000 psi, #4 rebar 2 ft on center.

I specified that my wife & I would place the rebar as they pour & that I would buy all the rebar.

After getting a few very high quotes, I found a guy who would do it my way and liked what I wanted to do. He had a few ideas that we used to improve my initial plan.

You are correct, you can not drive a concrete truck over rebar, it bends it up. The chute will reach a long way (20+ft), or they can order a truck with a conveyor belt system that reaches 44 ft (approximately).

For your driveway, two pumps it ridiculous in my opinion. By proper planning, a good crew can do your concrete pour without a pump. Also a crew of four can very quickly place rebar & wire tie it together.

I used plastic chair, but in the future, I will use concrete dobies, the plastic was too tall for the 5 inch thickness, a 2 inch tall stone/brick would have been perfect.

Oh, I vote for rebar also. If you get cracks, it will hold the driveway together (and everyone says it will crack)

brownbagg

As a foundation engineer, rebar is not needed. they is not enough concrete or load factor to justifed rebar. Rebar works by counting acting the load factor which bend the concrete. On a typical driveway there is not enough concrete coverage, to counteract the bending. By placing correct space controlled joint and having a compacted sub base, cracking will be minimum. You can always increase the thickness for a safety margin.

There is really no need for rebar.

mrpowderkeg

I would rebar it. Not trying to go against what brownbagg said, but it kinda covers what he stated, it all depends on the base you begin with. It appears you have good drainage, but does your soil retain water and get mushy? I don't think freezing and thawing would be a factor where you are at, but if you get a rainy season and the ground gets saturated it could play into if you would want rebar.

Personally I would use rebar, along with fiber mesh mixed in with the concrete. But this is coming from someone who lives in ND, where the winters are harsh on concrete, and heaving and cracking is common.

Stuart in MN

I'm no concrete expert, but for what it's worth: my driveway has mesh in it, and it's made it through nearly 20 years worth of Minnesota winters without a single crack. However, I suspect that has more to do with proper preparation of the ground underneath before it was poured.

drmoonshine

Rebar is your best bet. Mesh works though I used it on a concrete table and it works fine.

rickycobra

I have mesh enforced concrete that I poured in my backyard still around today only five years old. However it has cracked in only one area so I cut up the section once the concrete crack got bigger. Truth is concrete will eventually crack or chip it's just when will it happen.

brownbagg

Not trying to give a design answer but the way rebar work. concrete is strong in compression, rebar is strong in tension.so with a slab with rebar The rebar is doing nothing till a load force is applied. This will curl the concrete slab or bending and once the concrete cannot hold the force it will crack. The rebar is being pulled on its axis and counter acts the bending of the slab. note: concrete runways for airport has no rebar in it but they are 12 inches thick.

so its a question of economic. "4 are 1/2 inch rebars, sothat be one inch of steel at the cross over. you need 2 inches under bar and 1 1/2 inch above bar, so that4 1/2 inches of concrete. so let say 5 inches. Plain five inches will hold almost anything with out steel.

so you have to calculate how much it will cost in steel compared to adding extra thickness of concrete.

if it was me and I had plenty of money in the budget. I would add rebar, but looking at the calculator, it not needed.

Torque1st

My 1890 sf was placed over a well compacted base at 6-7" thick with rebar and fiber. The fiber only section cracked within days.

My old drive was poured at two times. The original 4" section was placed with standard 6x6 mesh and had many cracks. The newer 6" section was placed with state highway (heavy) wire mesh and rebar on the perimeter. It stood up to heavy trucks with only one small stress crack over a tree-stump void. The mesh was also placed correctly at the midpoint of the slab. I was able to observe the mesh when the drives were torn out for some road work. In the original slab about half of the mesh ended up on the bottom of the slab.

Concrete without reinforcement has almost no strength in tension.

toolfreak

I would use rebar, not a fan of mesh. Concrete will always crack, it's just a matter of controlling it with control joints. We always cut the concrete the next day while it was stilll green.

ddawg16

If you do a search on concrete and rebar....you pretty much get the same response...some say yes...some say no.....all say it will crack at some point....and all agree that given the 'realitive' low cost in comparison to the concrete and the fact that you can't put it in 'after the fact', might as well do it up front.

This is the way I see it....we all agree that the rebar is for the tension strenght...not compression....

It's for a driveway...cars and trucks will be driving on it. The average car weights a little over 4K lbs? That works out to about 1000 lbs/wheel...so that is 1000 lbs pushing down on a few square inches of concrete. If you base is good and stable...the ground is helping support that weight.

But lets say that a water leak has eroded the soil out from underneat....with that 1000 lbs on top...it pushes down...the top layer of concrete goes into compression...the bottom layer goes into tension....if rebar is installed...it absorbs a majority of the tension....no rebar...your at the mercy of the concrete....

Once you pour that concrete.....your not going back later on to install rebar....

z28toz06

I would never pour concrete without mesh or rebar. It's only a matter of time if you don't. I have been in hundreds of homes and you can always tell which ones don't have rebar.

rodnok1

Proper base/sub base and compaction is more important than wire mesh or rebar. Personally I hate wire mesh and dealing with it. rebar if you're gonna do one or the other.

Bruce4310TX

Get new bids, you dont need 1 or 2 pump trucks sounds like there preying on the uninformed home owner. Use a power buggy or wheel barrows. and use the re-bar mesh ends up on the bottom.

hilld

My concrete guy once told me. There are two types of concrete, one with cracks and one that will crack. Unavoidable in his mind.

Have you thought about fiber mesh in the concrete instead of rebar?

popcorn-guy

Trees. Bad for driveways, sidewalks, patios and foundations. One might consider cutting the existing roots that are causing the current trouble and get some relief for a number of years at least. I agree with those that have suggested excavating and placing base material and sand with compaction then pouring the concrete. As for choosing rebar or wire mesh, pick your poison. I would consider either and determine where the control joints would be made for crack control and place the iron as seperate panels within them. I would think that it would tend to reduce the chances of cracking (perhaps) within the panels and utilize the control joints to relieve the stress.

I just completed a paver patio to replace my front lawn due to gophers. I used 4" of base rock compacted with a vibratory plate and then approx. 2.5" of sand compacted as well prior to placing the pavers. I also (tip) used a layer of unfaced fiberglass under the base to prevent the gophers from coming up through the materials. Gophers are hemophiliacs and will bleed to death if they cut themselves and that would be with fiberglass. I would use "rock wool" the next time which is fiberglass in small tuffs that are blown in attics for insulation. Much easier to cover the ground with them and easier to compact as you don't need as much. Just a barrier. We haven't seen gopher action since. A large fir tree had been in the yard, which we had removed previously a couple of years ago, but found very large roots that had to be removed to be able to lay the pavers. I'm quite sure they would have been an issue down the road. We both live in the basic area of No. CA and have similiar weather, other than summer, so we do not have to deal with freezing weather and the ground heaving that others face each year.

Pavers could be an option for you and would be worth while to investigate. Everyone has contributed good information based on their experiences and perhaps compiling those will provide the answer.

One persons input from a cranky old man with some lifetime experiences of his own. The best to you in your venture.

Torque1st

Rebar can be continuous through the control joints. It will also keep the sections from lifting or dropping with respect to each other. I had control joints cut in my drive. A month after my drive was placed I had a 66,000 pound truck driving over it to deliver gravel. Last week I had another 26,000 pound truck on it. No cracks have appeared except the original crack in the non-rebar reinforced section. The approach had fiber in it but IMHO it is largely worthless as a reinforcement.

Tree roots and stumps also create voids under the concrete when they rot away...

Daniel Dudley

I always overdo reinforcement, but lots of guys would just use the fiber strand reinforcement nowadays. Compaction is key, and making sure you have proper control joints properly placed. Proper ratio of water in the mix makes it stronger, but making sure the concrete does not dry out for at least three days is absolutely critical to getting full strength.

The engineer is right though, and Popcorn guy has a good point with the pavers and cutting the roots. Why don't you go and look at some of the driveways your concrete guy has done ? That would tell you a lot right there.

dan76

Might want to consider other alternatives than concrete.

Several years ago I did a driveway (20'x100') using concrete pavers. I got an excellent price on the pavers and the sand/gravel used for the base was nearly free. The major cost for the project was the compactor rental as I used it several times. Yes it was a lot of work, but the result was impressive and a major selling point when I sold the house. As I was determined to try this novel approach, I didn't get bids for a concrete surface........which I regret since a cost comparison would've been interesting.

Since the pavers were an open design, I spread a sandy loam top soil over the surface filling the open space. We then spread grass seed over the dirt and kept it moist. Within 20 days the "concrete" driveway disappeared and looked to be an extension of the lawn.

At last report the current owner of the property is pleased with the results. She reported no settling has occurred though she often drives a diesel pusher RV over the surface. She did tell me she had the grass replaced with a slow growing variety as she was getting tired of "mowing" the driveway.

mesh or rebar in driveway?

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