Casting Large Concrete Pavers

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I am about to start a project where I plan to cast a number of large concrete pavers in a mold for a patio and a walkway. The pavers will be 2" thick and vary from 2'x4' to 2x8'. Each paver will have embedded 3/8" rebar and remesh for reinforcement. I also plan to use some synthethic fibers mixed into the concrete as well to prevent cracking. I am debating if water reducer would be needed.
I am using the bagged Quikrete you can get at the Home Depot. My issue is to whether to use the regular or the high early concrete. Faster cure time would help me get the project completed faster. However, I am worried that the high early, since it cures faster might be weaker and more susceptible to cracking. My biggest concern is that cosmetically the pavers look good for as long as possible.
Does anyone have any experience with this process, or have any suggestions that would help produce a casting with maximum longevity?
Thanks,
Naveen
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snipped-for-privacy@gmail.com wrote: The pavers will

I would suggest that a 2'x8' paver only 2" thick is not likely to last long without cracking unless you have an outstanding foundation and very light traffic.
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wrote:

I would not refer to a 2'x4' or larger concrete slab as a "paver". He might as well just cast his walkway in place. Just moving such a piece of concrete,rebar or none,is liable to crack it.
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I've moved 2'x4' several times, and even thinner pieces than the 2" the O.P. is planning to cast.
That said, the 2'x8' will be considerably more interesting... But I think doable.
However, 2" thick is adequate for a walkway on a good base, but I'm skeptical of its use for heavier loads.
sdb
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wrote:

Agreed!
Ivan Vegvary
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On May 18, 7:09 pm, snipped-for-privacy@gmail.com wrote:

Greetings,
If I was going to make something 2'x8' and only 2" thick that I wanted cured quickly I would look at making it like ferro cement and NOT like poured concrete. Ferro cement is commonly used to make boats and water tanks which have strong thin walls. The process basically involves tacking rebar together and then coating it with as many layers (5 or more on each side offset from each other) of chicken wire (attached to the rebar with hog rings) as you can manage to squeeze high cement mortor through (1 part cement 2 parts fine sharp sand). You can then steam cure the slab for 24 hours and it should be ready to put into immediate service.
Hope this helps, William
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replying to deans, william bardsley wrote: Probably a good idea to cast in place. On that 2x8 if its doable, cut a control joint even a thin one and hope that is where it cracks. Fiber is great and a little thicker is good to if you cast in place. Let the concrete cure for 3-4 days before moving. 6 6 10 wire good if u can keep it centered in the 2" of concrete. Use the standard 3500 pre mix and throw a shove or two of portland cement in with the blend when mixing. MIX GOOD!!!! That is very important!!! See U can do it cheaply like u wanted but must make the work to do it!! Good luck.
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2'x8'x2" will weigh about 400 pounds and will require about 2.66 cubic feet of concrete which will require 5 80 pound sacks of premixed concrete (make sure you are not pricing or considering the 40# or 60# bags).
Anything made of concrete that is long and thin will probably crack.
Rebar should have 1 1/2" of cover. You will have less than 3/4".
Regular sacked concrete is about 2500 # concrete, the minimum allowed by code for foundations. Prestress concrete runs up towards 6000#. Most commercial concrete is 3500 with air entrainment.
There are special processes to create what you are after, but they require exotic concrete blends, special procedures, and technical curing. You can probably produce them if you do a bit more research on what will be required.
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Thanks for the responses so far. I would not have thought of idea that I am proposing, other than I have seen this type of work done in a number of homes here in Los Angeles - albeit expensive ones I have seen on architectural tours. I could not afford the cost of having some one else fabricate custom concrete forms and then have them installed. The only reason I am attempting something like this is that is looks fantastic when the paver/slabs are in place and some sort of ornamental grass such as dymondia is alowed to grow in between the spaces.
Basically the site on which I will be installing these paver/slabs is very hard clay with little give. I expect there to be normal to light foot traffic. The idea with the 2" thickness was to limit the weight so that I could physically install the slab. Additionally, with the paver/slabs that I have seen, they all appeared to be roughly 2" in thickness. I actually cast one that was 2' x4' and was able, without too much trouble to pick it up and move it into place.
I was hoping to solve the potential cracking issue by either adding a little thickness to the paver/slab, using a littl more rebar, fiber or simply curing the concrete wet for 30 days.
Naveen
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On May 18, 9:14 pm, snipped-for-privacy@gmail.com wrote:

Greetings,
Have you considered pouring a flat concrete slab to go under your ornate concrete? This might sound crazy but when it cracks you might wish you had.
Hope this helps, William
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I don't think 2" is nearly thick enough for pavers/slabs that large. I would make a good foundation and pour 4" sections in forms where I wanted them. Neither rebar, fiber, or long curing will prevent cracking of a section like you propose, even if you do not move it. Be aware that fiber will probably prevent a smooth surface and rebar would be very difficult to keep within such a thin section over 4 or 8 feet. The rebar would also be likely to rust and cause the concrete to split because of inadequate concrete coverage.
Overall, my personal opinion is that this is not a good idea at all.
Don Young
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"very hard clay with little give"
Clay is one of the worst sub-bases available. Very expansive when wet. Gauranteed to heave and crack your pavers.
Ivan Vegvary
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wrote:

It sounds like you are in way over your head. You need a LOT more study.

Very poor base. Proper base will be done by excavating and putting in a few inches of compacted 3/4" road base, perhaps topped by compacted and leveled sand. Finally layer an inch or so of moist sand screeded to height. Then lay and bed the pavers in that base.

Can you guarantee that? Or is this adjoining or near a driveway where a vehicle might drive onto it? If really only foot traffic then a base of 2" compacted 3/4" road base will probably be enough. (Still need the inch or so of moist sand screeded, into which to bed the pavers.)

Buy pavers. They use lightweight aggregate, air entrainment, etc. to reduce the weight and cost and increase the strength.

Fiber or ferrocement would probably work, maybe remesh (10ga or so) but even 3/8" rebar in a 2" slab is iffy.
Don't forget some retaining method at the edge. Steel is nice, set down about grade (ground level) to about 1/2" above grade.
sdb
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On May 21, 4:59 pm, sylvan butler

The time of being in over my head is long since past. Two retaining walls, french drains, and 80 cu yard of excavation and removal of dirt and rubbish and I am still going.
I can guarantee that there will be light foot traffic, since this is not a car accessible location. The only other weight would be normal patio items.
As far as the compacted gravel sub base with sand. This was the original plan, until we decided to plant the dymondia or some other ornamental grass between the paver slabs. I figured having a dirt base underneath would be easier to plant with. I was also hoping that the strength of the concrete would be able to overcome any shifting of the earth. I suppose I can some scoop the some of the sand out from the perimeter of each paver/slab once they are put in place, and replace with soil.
Does anyone have a recommended minimum thickness that the paver/slab should be. If I increase to 3.5"-4" thickness will this work with the 3/8" rebar, mesh and fiber? I know this will be quite heavy, but I can reduce the size of the paver/slab to be roughly 2' x 4', or maybe slightly smaller so that I can get them in place.
I am looking to price out how much casting these paver/slabs would be. Though the the rapid set strong concrete sounds like an interesting option, the cost becomes prohibitve quite quickly, and making the effort not worth the time. My initial hunch is that pprecast pave/slabs will be expensive, which is why I decided to undertake this project in the first place.
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wrote:

It doesn't sound like it...

Good. But you evidently don't know pavers.

With 2" thick pavers, the base doesn't much affect the grass growing between the pavers.

Best to treat concrete as a wear surface. The base is critical. If you don't have a base, think "bridge" and imagine the large concrete and steel beams necessary for even a foot bridge.

With 1" of loose, screeded sand as I described, there will not be significant sand between the pavers to "scoop out".

3" would be fine. Generally if the rebar has over 1" of concrete on all sides it will be OK in a mild, earth-bound climate.

You can move a 400lb concrete slab? Impressive.

Check out the price of buying pavers.
sdb
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On May 23, 3:02 pm, sylvan butler

I meant I have been in over my head ever since the project started...........
So I will plan on putting in at least a 2" compacted gravel sub base with the 1" layer of sand on top. I will cast the paver/slabs at a minimum 3" thickness with 3/8" rebar and remesh. This is SoCal, so the weather is temperate and generally dry, and would have lesser impact on the concrete/rebar than in other areas.
Does anyone know the shape the rebar should be in for an application such as this - bent so that it runs offset a few inches along the interior perimeter of the paver/slab or should there be a bar running down the middle as well? Any thoughts on using galvanized, or any other coated rebar?
I was not against reducing the size of the pavers/slabs, down from my initial plan. I just wanted to explore the pitfalls of my design before I started. It looks I will have to reduce the the size ( the 2'x 8' are absolutely out) of the paver/slabs because of longevity and weight considerations of concrete. Based on my measurements and the gaps between the the paver/slabs for the planned area, the reduced size of each paver/slab would be about 21" x 44".
The reason I am intent on these large style paver/slabs, is in essence, to match the style of the house. This a 60's modern house, and there is not a whole lot on the market in tems of pavers that the match the clean look that I am going for. Many of the precast products are very traditional/tuscan/country looking and frankly would be a mismatch. The really basic plain pavers tend to look pretty generic and institutionalized. If anyone can point to a source for something like I am trying to achieve, I will gladly buy it.
The other option is to have a contractor come in and do a custom job, which will probably cost an arm and a leg. Given the that patio area is roughly 275 square feet, I think this doable.
I bought this house with what was essentially a junk pile for a backyard, which had never been used. I am trying not to spend an inordinate sum of money on this work, becuase I feel it would add little market value (but a ton of personal utility) to the house.
Naveen
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wrote:

I prefer what is called "3/4 road base" around here. It is a mix of crushed (not round) gravel from 3/4-inch down to dust. It compacts. Round gravel and even sharp gravel without fines does not compact well.

If it were me, I'd go back to 2", forget the rebar, use fiber mix 'crete and 10ga remesh cut to size of the paver minus about 1-1/2-inch from all the edges.
I'd prefer to take the time and do a test cast of a 1-inch and a 1-1/2-inch paver works over that solid base. With just foot traffic, I think it has a good chance to be OK.
You might be able to cast the pavers in-place over the base, and just remove the forms from between and fill in the gaps with dirt. No moving big heavy slabs. :) (I'd form up with 2x4's in a nice grid pattern, then fill in all the "paver" spots with concrete. Remove the 2x4's the next day. You could even have the concrete delivered, since you'd be placing the entire batch at once.)
sdb
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Actually I've seen a concrete slab something like 2'x6'x2" supported at both ends by cinder blocks with three guys jumping on it in the middle. It actually bend about 4" in the middle and spring back to original shape when those guys got off - no cracks and seems to be indestructible. Flexible concrete! Don't remember the composition but I believe it had lots of fiber mixed with the concrete.
Like someone said your small one is about 200 lbs (2.7 x 60 lb bags plus rebars plus water) and the large one about 400 lbs (5.3 x 60 lb bags plus rebars plus water) and will crack without some very special treatment. Also unlikely you could lift these slabs by yourself like pavers all day long without screwing your back.
I'm doing pavers myself but its more like 1' x 2' x 3". I'm using a concrete vibrator, no rebars.
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snipped-for-privacy@gmail.com wrote:

I know next to nothing about concrete, other than a few tips learned when speaking with contractors when my hubby was building manager for our condo. If I was pondering a project such as yours, I would use smaller pavers and no rebar. I'm thinking that the thickness of the concrete over the rebar will be only about 7/8" on either side. Seems likely you would end up with a lot of burst concrete from the rebar rusting and no surface strength along the rebar. I like pavers with grass as you describe, but I would be inclined to use smaller pavers and forget the rebar.
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Sorry to burst your bubble, but with a response like that you obviously know far more about concrete than you give yourself credit for.
R
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