Concrete drying time?

[klm0462]

On May 1st we had a 6" thick concrete pad poured for our 5th wheel. The 5th wheel is parked behind the pad right now, and we have a camping trip coming up on May 17th. I was wondering if the pad would be completely dry by then to drive and park on? We live in Deltona, Fl.

[Vicr]

What PSI concrete did you have poured?

[Grumpy]

Rule of thumb is 7 days.

[Jagiven]

I just added to our pad. Our concrete guy said 7-10 before parking on it. No problem driving over it within 7. Just be carefully turning the wheels as it will permanently mare the surface with tire scrubbing for the 1st month.

[2nOZ]

We had a pad poured for our 5th wheel last year. Our concrete guy mentioned 10-14 days but we are in the Midwest.

[NC Roamer]

Here are general concrete curing times unless weather is cold.

[wags999]

At least a month for full cure....but should be able to drive over it within a few weeks.

[brettt]

In Phoenix we were able to speed up the cure by misting the concrete with a water hose.Pretty sure we were on it in 3-4 days!

[Vicr]

The higher the PSI (the mix) the faster the cure time.

[wags999]

Actually we mist to slow down curing..if you do not the top dries too fast, same reason they pour foundations at night during summer. Concrete takes a month to fully cure. You don't want the top to cure too fast.

[klm0462]

PSI was done at 3000 PSI.

[Shackrat]

Originally Posted by klm0462

PSI was done at 3000 PSI.

You can use math to determine when it's safe to park on it. You have a trailer that weighs X, that weight is distributed over 4 tires, each has a physical footprint, plus two front landing gear with a footprint.

A standard 16" RV tire has approximately 32 square inches of contact surface. There are 4 of them, meaning about 128 square inches of weight distribution, not counting the landing gear.

On my GroundControl system, the landing gear they have about an 8" pad at the bottom of the jack. That's approximately 50 square inches, but since there are 2, that's 100 square inches.

128"sq for tires, and 100"sq for landing gear equals 228 square inches of contact surface.

For the sake of argument I'm going to assume that the trailer weighs 15,000lbs... Divide that up by 228 and you get the approximate force the trailer will be putting on your concrete, or about 66lbs per square inch. Not bad, right?

But I like to calculate the force applied to each contact patch since it creates "hotspots" of load on the foundation under the pad which can lead to failure of partially cured concrete. Assuming even weight distribution, each wheel in theory would carry 2,112lbs of weight, while the landing gear about 3,300lbs each.

There are other considerations too.. Whether the ground under the pad is soft fill, how much reinforcement was used, etc. Plus, we also know weight is not evenly distributed across the all contact surfaces of a trailer so to play it safe you want to leave a very, very large margin.

All of that said, after a 2 week cure at 90%, it will be be more than safe to park on it.

[gypsmjim]

Originally Posted by wags999

Actually we mist to slow down curing..if you do not the top dries too fast, same reason they pour foundations at night during summer. Concrete takes a month to fully cure. You don't want the top to cure too fast.

When I read that I spit out my beer......LOL.

Concrete requires water to cure. It's an exothermic chemical reaction. Thus, the exotherm causes evaporation, and a slower cure. As such, we mist the concrete to make it cure faster and cure stronger.

If concrete "dries out", is cures slower and has poor strength.

See the previous post for excellent data on the cure rate. Drive across in in 7 days. Park on it in 14 days. Build the house on it in 28 days. You want that last 1.0%. You may not live long enough to see it.....LOL.

[JesseS]

RV pads are a general 6 sack mix unless otherwise specified, misting every couple of hours in the daytime for the 1st 3 days will slow down the curing but prevent scalding or stress cracks from the exterior curing faster than the interior. 5er's are heavy and the landing pad concentrates weight in a small area, so give it 2 weeks and use landing pads to spread out the weight for a month or two (or always). A lot depends on area prep and how much rebar was used.