About 25 years ago, we blasted a flat spot into some solid granite
on a lot near Burnet, TX. and set up forms for a driveway with great
difficulty. We used #4 rebar in a grid pattern, 16" OC each way.
Poured 5,000 PSI concrete 5" thick. Waited 5 days and drove large
trucks over it with no problems.
Had a neighbor that poured 3,000 PSI concrete 3" thick with WW
mesh. Wet it down for a week after the pour. He did NO surface
prep, didn't even remove the carpet grass under the slab. Cracked
the first time he drove on it with his Geo metro.
Go figure.
--
Robert Allison
Rimshot, Inc.
Georgetown, TX
Concrete is an chemical reaction, which is slowed by cooler weather.
If it was my driveway I would wait at least 7 days.
I would not put heavy load on it for at least a week, during which
time it should be kept moist.
Robert Allison <robe...@ix.netcom.com> wrote in message news:<41A17EA6...@ix.netcom.com>...
One of the first expressways, the Davison in Detroit, was let to cure
for one year, and lasted 50 years.
rkpatt wrote:
>
> This one has good solid bse but only 4" with fiber additive and lots
> of control joint. The finished did not water down the mix.
Wait at least a week, but as long as you can after that, up to 14
days. You should be able to drive on it in a week. I just like to
hold off until I really need to get on it.
We have driven on driveways after 3 days with no problems, but I
would not recommend it.
--
Too late now but your best bet for a good cure was to water it heavily
and the cover with plastic so it would stay moist constantly. After 5
days it isn't going to much harder. If you really need to drive on
it, then put down sheets of 3/4" plywood to spread the load. 3/4"
plywood will protect lawn from an empty pickup.
Are you sure they were letting it sit for a year just to cure? Or
were they still working on it?
> Concrete cures to it's full hardness in 28 days assuming proper
> conditions (temp., proper watering, etc).
Are you sure you don't mean nominal hardness? I thought that
concrete normally kept hardening for years, asymptopically
approaching some ultimate value, and that the 28-days was just
the standard to which they test the stuff.. So that 5000psi concrete
is called that because it hardens to 5000psi in 28 days...
--Goedjn
That is correct. With most types of concrete, it cures to its rated
capacity in 28 days. It will continue to cure for about 100 years,
according to the experts. Some types are different (high-early
comes to mind, but for the most part, 28 days is the norm.
Are there any cracks from it? If not, then don't worry about it.
Doubt a little Toy is going to damage a slab that has been curing for 5 days.
Might be a bit concerned if the delivery truck pulled onto the slab with a full
load of shingles, but a bitty pickup? Nah....
Bruises, broken arm, bullet holes. Oh, you mean the slab.
If you don't see any obvious damage, then damage is
unlikely. 5 days curing in temperatures above 40 will
support a small truck just fine. Heck, two days at higher
temps would probably be ok.
Measurements I have seen showed about 70% strength after 2-3 days and
100% strength at 28 days.
Of course the type of concrete and the weather conditions will cause
variations.
I would wait a week to drive on it.
Steve
As to the "where" of cracking, a properly designed slab will first crack along
the joints (as designed). No contractor worth beans is going to pour a 20x50
slab without a few joints in there. Over time, you'll get cracking along other
parts of the slab (take a look at pretty much any >10 year old residential
driveway).