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New here. I wonder if anyone here can help me with supplies, dimensions, type of concrete, rebar type, and other things I will need to fill in a driveway area with concrete.

Story: So, when I bought my house, we paid extra for an extended driveway, but they didn't do the front part. I am now just trying to fill in those grassy patches.

Images: The first three images show the grass that I need to fill. The fourth image shows the rough dimensions of the grassy area.

Location: South New Jersey, cold and hot climate

I did some research before posting, and I saw that people said a driveway should be a minimum of 5 inches deep, with 1/2 fiberglass rebar. The concrete should be at least 4000 psi rated. Is this correct? Is there something else you would recommend instead?

This is the concrete we plan to use: https://www.lowes.com/pd/Sakrete-80-lb-High-Strength-Concrete-Mix/5013767297

Do I need concrete expansion joints, like from https://www.lowes.com/pd/Reflex-Rubber-Concrete-Expansion-Joints-Common-0-5-in-x-4-in-x-60-in-Actual-0-4375-in-x-3-9-in-x-59-9-in/3365434?

Does this rebar work: https://www.lowes.com/pd/Owens-Corning/5013333093?

I was also told we needed some rocks, about 1 inch minimum of rock under the concrete on top of bare top soil. Is that needed or not?

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    In many places, the sidewalk and the area between the sidewalk and the street and possibly a little more towards your house on the other side of the sidewalk is public (county/city/etc. depending on the type of street) property. If you are in a private community you won't have that problem but you may have homeowners association to deal with. So check your local jurisdiction (start with the building department or equivalent) to find out what you can/can't do before you order anything and before you put the shovel in the ground. Jul 21, 2023 at 3:14
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    Ah, thanks. No HOA to deal with here. I am going to check with my county, but I did some research and it looks like it is allowable as it is my property. I will follow-up with the county tomorrow to make sure.
    – Peter
    Jul 21, 2023 at 4:03
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    Is your property line right on the back of the curb? You need way more than 1" of gravel. You probably need at least 6".
    – Huesmann
    Jul 21, 2023 at 11:49
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    @Ruskes OP linked specific types of concrete mix, rebar, etc. Which means OP is planning on DIY and not a contractor. Which makes "get some contractor to give you the quote..." an unethical thing to do. Perhaps people asking contractors for quotes when they intend to do the work themselves is part of what has led so many contractors to not want to give quotes at all... Jul 21, 2023 at 15:10
  • If my calculation isn't totally wrong then alone for the larger slab you need about 25 bags or 900kg of dry concrete. Perhaps you have an supplier of mixed (wet) concrete in your area? That way you can avoid the tedious work (hauling and mixing) and concentrate on the core work (making the form, rebar, finishing etc.).
    – Martin
    Jul 21, 2023 at 15:23

1 Answer 1

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Your concrete choice and rebar should be fine. I think the fiber glass may be over kill, normal steel rebar should work too, depending on price, but it's up to you.

The important thing with the rebar is it needs to be attached to the adjacent pieces of concrete to insure they don't shift relative to one another. Get a 1/2" masonry bit with a hammer drill, these can be rented for reasonable cost, drill holes 2-3" deep into the sides of the adjacent pieces of concrete every 12" or so, care should be taken when drilling not to drill too near the surface or to angle up to the surface as you can crack the existing slabs. Hammer the rebar (~12" length) into the holes, it should be a tight fit, but again be careful not to break the existing concrete.

Your 'rock' layer should be 3/4-"three quarter minus" gravel and can be ordered by the truckload from any gravel/concrete supply place. The minus means they keep the fines from breaking up the gravel which will make it compact tighter than washed rock would. 1" would be pretty low thickness, depending on the soil type, I would say shoot for 4" of rock. Important when excavating not to undermine the existing slabs. The gravel needs to be very well compacted. Hand compactors will work, but I would recommend renting a mechanical one. Spraying down with water will help compaction and keep down the dust.

Place 2x4 forms along the outside edge and put wood stakes about every foot or so on the outside of the form. Secure the 2x4 forms to the stakes with screws to keep it at the desired height, which in this case should just line up with the existing concrete. Make sure the screws are from the outside stake side into the forms and not the other way around, otherwise you can't unscrew them after the concrete is poured.

Your concrete choice looks fine, keep in mind if using bags you're going to need a lot of them. My rough estimate, assumed your slabs are about 6'x6' and 6'x5' so about 66 sq ft 4 inches deep makes 22 cubic feet (5 inches pushes it up to 27) or a about a cubic yard (27 cu ft = 1 cubic yard), when estimating concrete always round up it's much better to have a little too much, I would order 1.5 yards in a ready mix truck. For reference if ordering in a mix truck they carry around 9-10 yards of concrete and most places will have an additional short load charge for less than a certain amount. This may still be worth doing as those bags are only 0.6 cubic feet each, making it about 40-50 bags, which if hand mixing in a wheel barrow is a lot of work moving bags and takes a long time. You can also have issues as you can probably only mix 2 or 3 bags at a time, so you have to mix fast so the concrete doesn't dry out in the hole before all of it gets mixed and poured.

Speaking of drying out you want to wet the existing concrete and the gravel just before you pour or the dry concrete and gravel can suck the water from your mix and dry it out really fast at the edges. Also you want to pour when it's not going to rain, but really hot days are actually not great either as it will dry really fast making the finishing difficult and very unforgiving for someone unexperienced. If possible pour in the morning when it's cooler out. Don't put off cleaning your tools. Have a wheelbarrow or bucket full of water nearby for this, note: not where it will spill into the concrete.

You are going to want to put some joints into the new pads to line up with the existing pieces. something like this to control cracking:

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For finishing you will need at minimum a trowel to smooth it out, an edger to round out the edge and a groover to make the middle joint lines. A string pulled tight and snapped onto the concrete works well for making sure you get straight joint lines. You shouldn't need expansion joint filler for the small outside bits you're adding.

When you're done pouring make sure it is marked off or you stay nearby as it can be marked up or otherwise have impressions made into it for several hours, even when it seems completely dry. After pouring a friend's patio we went inside to relax after the hard work was done, while unknown to us his 5 year old did circles on the new slab in his tricycle, It seemed completely dry but those faint circle lines are forever.

After about 24 hours you can pull the forms out and backfill the edges with gravel/dirt/grass. You need to keep heavy loads (like cars) off of the concrete for about 2-3 weeks, it's still hardening even if it looks completely dry, I would recommend a cone, garbage can or sign of some kind; or you might get someone driving on it without knowing.

Hopefully this helps, it's a lot I know, I've done way too much concrete. Good luck.

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  • Wow, amazing answer, thank you. What if we don't drill into the other concrete pad but just use an expansion joint as a separator? Yeah, I think we are going to use a wheelbarrow, but we are doing one patch of area at a time. Is that fine?
    – Peter
    Jul 21, 2023 at 17:44
  • Doing it in sections should be fine and will make it easier and more manageable, and if you have rebar between the sections should be fine strength wise. If not drilling into the other concrete you risk the new sections shifting over time, if not doing that, your gravel compaction needs to be perfect to prevent settling and may still shift over the span of years.
    – Josh King
    Jul 21, 2023 at 17:55
  • @Peter I did it once and will newer again. It is a back breaking work.
    – Traveler
    Jul 21, 2023 at 18:10
  • Will the expansion joints on all sides next to the concrete pads and sidewalk with like rubber or poly allow room to shift but not crack or affect the other pads?
    – Peter
    Jul 21, 2023 at 18:23
  • Also, I am curious why some people put gravel/rock while some don't, e.g. youtube.com/watch?v=enUJb9rs_78 They do the entire driveway with no gravel. Asking because you mentioned 4" of gravel.
    – Peter
    Jul 21, 2023 at 18:36

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