Around here, tradition is foot traffic in 24 hours, cars in a week, and
no trucks for a month. (and a loaded UPS truck is pretty heavy, one
reason they almost always double-park in the street, the others being
that backing up takes time and increases chances of an accident.)
But we can't see your driveway and soil from here, and we don't know how
the substrate was prepared, and what reinforcing was used. Call the
company that put the driveway in. They will likely have very specific
instructions as part of their warranty package. Did they cover it during
the initial cure with straw or plastic, or just tell you to hose it down
daily to keep it from drying too fast? (Or does modern concrete not need
that in warmer weather?)
No, it's not a moot point. Air cured concrete has about 30% of it's final
compressive strength in 7 days, about 50% after 28 days, and it gradually
increases from there over years. As you say, very close to a log function.
It's also important to get the correct mix and reinforcement. Cheap concrete
might be 2500psi - better to get 4000psi and then use rebar or steel mesh.
I worked on a pan crew for high rise buildings. We put in all the forms for
the floors. When we did a pour, we had screw jacks underneath the forms,
about 8' apart. You could not touch any jack for five days after the pour.
After five days, you could remove every other jack. (50%) After one week,
you could remove every other jack. After one week, you could remove the
The concrete in Hoover Dam is still curing. They put water recirculating
lines in there that are still functioning and removing heat from the curing
concrete, poured in about 1932-1935. IIRC, they projected the concrete
would be fully cured in 100 years. By now, though, I would think that the
percentage per year would be a percent of a percent.
I think your right and wrong. The concrete is still curing but the water
lines to take the heat away have since been filled with concrete to avoid
them being chocked down and when the heat level reached a certain point they
forced concrete in them before they were compromised.
replying to Robert Neville, FlyAsh Forever wrote:
You are correct, they take core samples from Glen Canyon Dam every five years to
compute compressive strength, it was poured in the early 60's and is still
getting harder every test cycle!
IGNORE the answer of driving on it after a DAY... foolish advice.
ya spend $big$ dollars for a nice job...
Why would you damage the concrete that should last for MANY years just to drive
on it a few days early?
There are molecular structures that have to form... drive on it and you damage
those structures, resulted in a failed surface.
replying to dwasylenko, SteveB wrote:
We in the construction industry in California give it a minimum of 2 days and
most likely 3 days before driving on it. We have driven on them in 2 days and
had no problems. We would not do any deliverys tho...
replying to Phisherman, Rodney wrote:
Please do not drive on the concrete after 24 hrs unless you want to risk
damaging it!! It is scientific too. The mix , site preparation and application
all make a difference to the outcome.. keeping an eye on it and wetting it down
in hot weather is a good idea as it prevents it curing too quickly as the water
content drops while the chemical reaction is strongest. This helps prevent
cracking and crazing. Concrete gets progressively stronger with time , that can
be years but is sufficiently strong enough for most domestic usage after 7
days,with care. Once it is cracked,or marked it is permanent. Patience required!
I wouldn't ever let a delivery truck drive on a 4" slab. Isn't 6"
standard for driveways? Or is there some newfangled additive that
makes concrete stronger?
[or is the extra cost of 2" just so low compared to the whole job that
it is just a good idea?]
ACTUALLY, you be lucky to find more than 3.5" in a driveway. That't the
height of a 2x4 thats used for forms. And it's always called 4".
Driveways are rarely 6" unless specially ordered that way. And a 4"
driveway is plenty strong for any city delivery truck. hell they backed
a full load of concrete in on mine to re-do the upper section and no
It's difficult to find a craftsman nowadays who can cut a grade for a 2 x 4
framed pour that doesn't run from 3.5 to 6 inches thick.
For me, I like to give it a full month before driving on it with a larger
than average vehicle. After that, whatever's going to happen will. Just
put expansion joints and saw cuts, and roll the dice.
And ......... as an afterthought, a half or full sack mix more than required
is cheap insurance.
YMMV, but mine is always right ............ ;-)
I had a concrete pad poured in my back yard to park 7000 lbs. 5th wheel
trailer and 3/4 ton PU truck. I parked both after 10 days since pad was
poured. Nothing bad happened. Really concrete cures LONG time; ~
100 years, gets harder and harder with time.
Absolutely, 100%, contact the ready mixed concrete producer (or the
contractor who placed the driveway, if you believe him to be trustworthy)
and ask them! In particular, the ready mixed concrete producer (the firm
who supplied the concrete in the truck that was delivered to your project)
will be able to tell you, and you should follow their advice by all means!
If you don't, you may very well regret it!
Douglas E. Ruhlin
Environmental / Sustainability Consultant, CCPf, LEED GA, REM, CEA
Resource Management Associates
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