Anybody knows about concrete?

[e9999]

So my neighbor put a concrete swale across our driveway. Told me I could drive over it after 2 days. Fine. Planned for that. It's poured. Last minute, one of the workers tells my wife it is 4 days. WTH? Of course, can't reach the contractor to confirm, everybody is gone for the long weekend. One stuck vehicle behind the barricade.

6" of concrete (don't know what kind but was pretty smooth, no big gravel) over rebars. Uncovered. Weather in the low 70s, partly cloudy during the day, around 60 at night.

In your opinion:

2 days or 4 days for

a) a Prius
b) an armored 80?

to drive on it without leaving tracks (tempting as it may be... )

what say you?

TIA

 

[ojaij40]

So my neighbor put a concrete swale across our driveway. Told me I could drive over it after 2 days. Fine. Planned for that. It's poured. Last minute, one of the workers tells my wife it is 4 days. WTH? Of course, can't reach the contractor to confirm, everybody is gone for the long weekend. One stuck vehicle behind the barricade.

6" of concrete (don't know what kind but was pretty smooth, no big gravel) over rebars. Uncovered. Weather in the low 70s, partly cloudy during the day, around 60 at night.

In your opinion:

2 days or 4 days for

a) a Prius
b) an armored 80?

to drive on it without leaving tracks (tempting as it may be... )

what say you?

TIA

Why not just stack scrap wood or bricks or? on each side, and drive over it?

 

[Michael Hanson]

Hi, I usually tell our customers 1 week, longer if there is a severe grade. complete dry about 28 days. Why didn't they let you get your trucks out before they poured ? Mike

 

[KLF]

I agree that it was thoughtless of the contractor to leave your vehicle on the other side, captive until the concrete is cured. Leaving tracks? Well, it will have an initial set after only a few hours to prevent that. But the concern you have is cracking. There's really no way to know how long you need to wait without knowing what's underneath, how well it was compacted, how much reinforcement, etc. I'd also have to see what's going on. But, if it were me, I'd probably wait at least a week.

Do you have some scrap 2x12's you can "bridge" across the thing? How wide are we talking about here? What day was it poured? For sure the contractor will have some, that's a common size for forms, but by the time you get them out there on Monday afternoon (at the earliest), they will tell you to just drive over it.

The strength of concrete as it cures is not linear, in general it will have 75% of it's strength in 25% of the curing time. Max design strength is calibrated for 28 days when doing the mix design.

 

[e9999]

a week...

this thing is 10 or 12' wide. not easy to bridge.

interesting bit about cracking. counterintuitive.

shoot!

we do have most vehicles out but left one in cuz 2 days was fine for that one

was poured wedn pm

so seems that 4 days is at the very least is not excessive

can do bike first then prius then 80 later?

 

[titanpat57]

what ever you do...don't take a picture and show us..


I'd mist it down until monday morning then I'd be out there..period

The longer you slow the cure rate down, the harder it'll get, and prevent cracking.

(maybe they poured the concrete with fiberglass reinforcing already in it.. )

 

[e9999]

I was thinking about a video actually. Showing the concrete drying... Maybe a slow mo?



there was no mention of misting at all. Or of fiberglass. But it's not my job so I don't have the details.


I was wondering about that actually and whether current concretes don't need the wet burlap treatment any more?

 

[WarDamnEagle]

I agree that it was thoughtless of the contractor to leave your vehicle on the other side, captive until the concrete is cured. Leaving tracks? Well, it will have an initial set after only a few hours to prevent that. But the concern you have is cracking. There's really no way to know how long you need to wait without knowing what's underneath, how well it was compacted, how much reinforcement, etc. I'd also have to see what's going on. But, if it were me, I'd probably wait at least a week.

Do you have some scrap 2x12's you can "bridge" across the thing? How wide are we talking about here? What day was it poured? For sure the contractor will have some, that's a common size for forms, but by the time you get them out there on Monday afternoon (at the earliest), they will tell you to just drive over it.

The strength of concrete as it cures is not linear, in general it will have 75% of it's strength in 25% of the curing time. Max design strength is calibrated for 28 days when doing the mix design.

what ever you do...don't take a picture and show us..


I'd mist it down until monday morning then I'd be out there..period

The longer you slow the cure rate down, the harder it'll get, and prevent cracking.

(maybe they poured the concrete with fiberglass reinforcing already in it.. )

What they said.

Why do you say that cracking is counter-intuitive? That's the only issue. It's not like clay or mud drying. Concrete undergoes a hydration reaction and as KLF said, much of the strength develops in the first few days. I would keep it wet (to prevent shrinkage cracks) and not drive on it for a week..........but that's just me.

 

[e9999]

I said counterintuitive because I would think that most people envision concrete drying as being too soft as first and hardening as time goes by. So, driving too soon would leave a mark, not crack it. So let's just say maybe counterintuitive for laymen, not for experts.

 

[PAToyota]

The thing to understand is that concrete does not dry - it cures. It is a chemical process. The longer you allow the chemical process to react, the stronger it will be. Keeping it wet is the way to keep the chemical process going.

 

[e9999]

The thing to understand is that concrete does not dry - it cures. It is a chemical process. The longer you allow the chemical process to react, the stronger it will be. Keeping it wet is the way to keep the chemical process going.

an exothermic reaction if I'm not mistaken.

And also why one can in principle pour concrete underwater and it will still cure fine reportedly, although I don't know the subtleties of doing that, there may be physical issues like stuff washing away or flowing.


anyway, looks like it's curing. at least the neighbor is smart enough to have sprayed it apparently.





added: somebody was able to reach the contractor. Apparently, he said only 4 days of curing before we drive over it. He did ask that we spray it 2x a day for a week though.