I am surprised to see people pouring that thick of concrete for a rv pad, mine is poured 4", 6 bag. My pad is 10 x 50 . Expansion joints 5 feet down the middle and 5 feet centers. No rebar, wire mesh, or other type of reinforcement . If you are compacted well under the pad you are good to go with 4" . My pad is nine years old gone thru 8 winters ( Utah ) no cracks or settling with a nearly 13k fifth wheel setting on it. Anything more than 4" is a waste of money and concrete.
I agree, my neighbor did the same for a 10 x 40 pad on the side of his house. But he did use wire mesh...it was a last minute decision....its worked out fine...Three winters later, not cracks, no problems. His boat weighs 8,000lbs and hist Trailber 7,500lbs their is alway one of them on the pad. It took him a couple of weekends. I want to do the same.
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Concrete at 4 inches is sufficient. The mix is the important part. If you do not specify the type of concrete, they will send you 2500 lb. mix (good for sidewalks only) You should use at least 3500 lb mix on your pad. I would rather see you use 400 lb. mix at a 4 slump, it is very dry coming out of the truck but will provide the most strength. What ever you do use 6x6 wire mesh and make sure to pull it up into the middle of the concrete with a rake. Do not allow the finishers to tell the driver to add more water which would make it a 6 slump or better, water just makes the concrete weaker but easier to flow into place thus less work on them. 4 inches of 4000 lb. mix at 4 slump is stronger than 10 inches of 2500 lb. mix.
If you are in an area that frezzes you want a min of 5-7 % air. it wont crack as easily. Order the concrete from a plant close to your house so it doesnt loose the air content. 3500 lb concrete is what I would use.And a good solid base.Its a toss up about wire mesh and fiber.4 inches is okay if the rest is right.
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Mine is 20' X 50' and is only 4" thick with rebar around the edges. It's 5 years old and no cracks.
The key is proper preperation. Most fly by night operations quoting a job for forming and materials will skimp to save money and you'll end up with 2" in most parts of the slab if you don't watch them close.
Down here concrete driveways are only 4" thick and you don't see them breaking apart.
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From my experience, knowing the type of soil will impact the design. For instance, I have a highly expansive clay soil, and it cracks the concrete. In fact, concrete always cracks and the frequency of the control joints can help to hide the cracks, but concrete does crack.
My driveway has 12 inches of class 2 base, with 6 inches of concrete, and #4 rebar on 12 inch centers, and I never park anything heavy on it, and it has lots of cracks. Due to this experience, two other parking pads that I've recently installed, I used 8 inches of base and two inches of ashphalt. This area doesn't have as much clay, but with the ashpalt it's easy to dump a bucket of slurry every few years, and it looks great. And alot cheaper too!
Lastly, let's do the math. If the 5er weighs 12k pounds, and each tire has a contact area of 25 sq. inches then there's 120 psi. 5 sack is rated somewhere around 2500 psi, I don't know the rating of ashpalt. Hope this helps.
The thickness of 4" or 20" is not as important as the mix.
Concrete in our area comes in 3000 psi/3500 psi/4000 psi/ 4500 psi, etc.
A lot of the batch plants short, or "dry" ship, the mix to the job site.
That means extra water must be added at the site and mix takes longer.
Needless to say the drivers don't like to take the extra time. Depending on how far you are from the batch plant, this could be another serious factor.
I recently, within the last year, poured a foundation for a new home, that took 125 yards. My drive way is 160 ft long and 14 ft wide, and it took about 35 yards. I had them bring out 4000 psi mix and it's 4" except on the edges which is 6". The rebar is #6 on the edges and #4 down the center, set on 16" OC.
The concrete contractor guaranteed me in writing that my 12,000# 5ver would not crack the drive. But I don't keep there all the time, just when I bring it home from the RV parking lot to prepare for a trip.
Bottom line, there is absolutely no reason that a drive or pad with #4 rebar and 3500 psi mix won't be satisfactory an RV up to 15000#s
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