Concrete Driveway - Anything I am Missing?

[larry4406]

I am planning on a concrete driveway between my house garage and detached garage in Northern VA (mild winters). I am currently planning on the following: 4000 psi air entrained concrete, 6x6 welded wire mesh, 4 inch slab, 4 inch of compacted stone base, control joints every 12 to 15 feet, broom finish, minimum pitch of 1/4 inch per foot for drainage, turn down of the pour at the garage entrances and doweling of the driveway to the garage slab to prevent differential movement, and expansion material between the garage slabs and the driveway. This will be a large area, approximately 110x60. I intend to stay off of it for 7 days with car traffic only.

Given the size, may not be able to complete this in one pour. What should be done then at the cold joints to prevent differential movement? Dowels?

I am debating adding fiber to the concrete mix but have heard about the "hairs" showing on the finished surface and not sure what effect I would get with the broom finish.

Is there any advantage of putting 6 mil poly on top of the stone? I would think the poly would help to keep the mosture in the slab, rather than wicking into the stone, which should help with the cure. Given the size of the pour, and not wanting to marr the finished surface, I probably will not be able to cover it.

What about curing compounds and sealers?

Thanks for any input.

 

[jamm]

WOW, that's a hell of a driveway. What are you planning on parking on it?

Since it is outdoors there is no need for poly, it's used to keep moisture from coming up from the ground not down. Just keep the slab misted down for a day or two.

Watch your slump and air entraining. Don't go higher than 6" or 6% respectively.

If the pour is not continuous use dowels at the construction joints and radius the edge. Your can even caulk it later on. You should decide before you start pouring if it will be continuous or not so you can set forms. Cut control joints the day after.

Make sure you broom it in the right direction for run off. Nail 5 or 6 broom heads to a 2x so you can cover a large area. There's nothing worse looking than looking at a slab with crooked broom marks. Remember it's there forever.

You are covering a large amount of green space with this drive have you considered where the water will go if you get a huge downpour. You definately don't ant to be responsible for flooding the neighbors basement.

Good luck and send in pics.

 

[scotw]

do you need any irrigation piping or electrical conduit under the slab?

 

[larry4406]

jamm - thanks for the slump and air entrainment limit, I will look into these.

I friend of mine is a concrete contractor - I helped him build his house, and in exchange he is going to do the drive for me for the cost of the concrete and wire mesh - no labor.

The plan is to prep the entire area, then make decisions as to the number of pours. I would prefer a single pour so as to avoid cold joints and minimize the potential for color mismatch.

Your right this is a big pour - it connects my detached 4 car garage to my house's 2 car garage. The garage doors face each other, so a very large courtyard if you will. The water will be channeled to the existing swale, albeit it will be faster than the dirt/gravel it currently flows on. Will take pics, at some point I need to learn how to resize and post here.

On the control joints, the contractor typically scores them as he is finishing rather than cutting them - any pro's or con's either way?

Sounds like the poly under the slab is not useful in slowing down the cure? How about for prevention of ground water wicking up through the inevitable cracks that will occur?

Fiber mesh? Good? Bad?

scotw - I think I am good on conduits - detached garage has 100A service, underground propane, phone, and data all installed and in conduit at all crossings. No irrigation system planned.

 

[rburke65]

Electrician here and I have placed my share of concrete...for the price of 10 sticks of pvc condiut, you will never regret running it under the drivewat. this way you get your **** covered if down the road you want to put in lights or a photo eye or????what ever. Once you out the concrete down........Just a thought.

 

[pmiranda]

I agree on running some conduit ahead of time just in case. One for plumbing, one for electrical. But I'm insane. I ran 2" conduit through my new attic for home theater wiring

Oh, and I think a broom finish looks awesome, especially if you smooth the outside 4" for a clean trim around the edge.

 

[Herb]

Well, the poly on top of the stones, under the concrete, DO IT! Many people will tell you not to bother, it's a waste of time and money, serves no purpose, etc., but it absolutely does slow down and to a great extent, eliminate migration of the water out of the concrete as it cures. That will only make the concrete stronger- and that is a good thing.

 

[KenS]

To avoid standing pools of water-- which become ice skating rinks in the winter-- be sure to slope the finished pour to a miminum of 1/8 inch per lineal foot minimum to shed runoff. Be painstaking to slope away from walkways, foundations, carports, garage entrances, and toward proper drainage areas. You might consider crowning the pour slightly to evenly shed water from both sides of the finished drive. Be sure your gravel base is properly graded.

If you can envision any future need for underground electrical service, phone lines, cable television, internet lines or water and sewer lines, trench for and install the conduit and/or plumbing lines now. It will only cost a few dollars compared with cutting through the concrete, trenching and burying future lines-- in the process leaving an ugly scar in the repaired area. If anything, oversize the conduit and simply cap it off for the future. Remember that live electrical service lines can't share the conduit with signal cables.

Be sure you know where the finished lawn grade will be so the finished drive grade is not below grass level.

 

[boiler7904]

I think you're too thin on the gravel base and concrete itself. I'd go minimum of 6" gravel and 5" concrete with wire mesh. Just because it's only car traffic now doesn't mean you won't need to have a truck on the drive for something in the future. It only takes once to really screw up an otherwise perfect driveway.

6600 sf is too much to pour in one day without a construction joint. How many guys does he have lined up to finish it? We normally limit pours to about 3000 sf continuous in one pour. Run a construction joint down the middle and you'll be fine.

Definitely run a conduit or two across the driveway and into the lawn. Never know when you might want landscape lighting or something else on the other side of the driveway. Your wife will come up with a brilliant scheme about a week after you pour the driveway. Believe me on this one. I can hear it now. Wouldn't it be great if...?

Vapor barrier under an exterior slab serves no purpose. The Concrete Institute is questioning if vapor barriers actually contribute to slab curling while the concrete cures differentially.

If you have radiant in floor heat, you might consider adding a couple of loops in the drive so you don't have to shovel snow between the buildings. You could always add the equipment later. Not so easy with the PEX.

Have you thought about coloring (integral or powdered broadcast) the concrete so that it isn't a big gray expanse?

Fibermesh will definitely alter the look of the broom finish - not for the better in my opinion.

Scored control joints are ok as long as the depth of them is equal to 1/4 of the slab thickness.

 

[larry4406]

Thanks all -

Still on the fence with the idea of poly under the concrete. Responses have been from no (possible contributor to slab curling) to yes (reduces mositure loss improving cure and strength, weed block, etc). My contractor has no experience with poly on outside concrete. I will be using geotech fabric under the stone (Amoco 2000). The area has been a gravel driveway for the past 9 years and is well compacted. The detached garage is complete with 100A service (in conduit), water, sewer, phone, data lines, and propane all installed. I even ran a fiber optic sewer camera down the lateral to ensure no bellies existed in the sewer line. Might place a few conduits for grins.

We met the other day and are thinking about this being 3 or 4 pours, so we have planned out where the cold joints will be as well as the striking of the control joints. All will be surveyed in to ensure we have a minimum of 1/4 inch per foot of fall.

Will not be using colors or tinting. I like the broomed white surface. I don't have radaint heat, so won't be going that route.

What is the best stuff to use as expansion joint material? The stuff I see in sidewalks, etc, appears to be about 1/2 inch thick and seems to be a fiberous cardboard which dissappears over time, weeds grow, etc.

Don't know if I can swing the $ to go to 5 inch slab. At one yard, a 4-inch slab will cover 81 sf whereas with a 5 inch slab, you only get 64.8 sf. Thus concrete costs go up by 25%. Here in northern VA, concrete is running about $110 to $115 a yard (highway robbery), so at 6600 sf, this would be an extra $2400+. I am on a very tight budget as it is.

 

[Kevin54]

I would not disturb the existing gravel base if you don't have to. If it is well compacted, then that is what you want. You don't need a weed barrier as the concrete will not let weeds grow through it. So that will save money. I'm not so sure I would even put the expansion joint in between pours unless your contractor recommends it. I WOULD pin one slab to the other and have it brommed then "picture framed" with the edging trowel. I'm in Ohio where we get deep frost and get frost heave. I had a sidewalk poured to my garage but did not pin it, but no expansion joint material. The sidewalk will raise maybe 1/4-1/2" in the winter then go flush in the summer. It has been down 7 years and not had a problem with no expansion material. Like you stated, after a while it rots out and you are left with a gap. All of my cement butts, cement to cement. Where I did have the expansion material I have about a 3/4" gap right across my driveway. It does come in handy though for dropping an extension cord in for Christmas lights though. LOL!!!