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Posted: Mon Jul 23, 2007 4:44 pm
by Phil H
Had my slab poured some 4 weeks ago.. had it covered and kept it lightly sprayed for over 1 week, everything appears to be ok. Have been on holiday for last 2 weeks i had left it loosely covered but on return from holiday have found that someone or somehow the cover has been completely removed, and with all this rain for last couple of weeks has certainly taken a wet pounding. My question, will all this rain so soon after being laid have any adverse effects on the concrete overall curing process.. The sectional building is being erected in next few weeks but not to be used for a while yet.
Interested in your views.
Phil
Posted: Mon Jul 23, 2007 9:20 pm
by lutonlagerlout
no problem at all phil IMHO
extreme heat or cold could be a problem ,but AFAIK concrete reaches its full structural strength after 1 week,and they build motorway bridges from it 
LLL
Posted: Mon Jul 23, 2007 9:39 pm
by Ted
I thought it gained strength quickest during the first week but really keeps on getting stronger during the first 28 days.
It then keeps on getting stronger but the speed it gains strength slows and as it is pretty strong after a month it is not that important whether it gets any stronger...
Posted: Mon Jul 23, 2007 11:23 pm
by lutonlagerlout
i had some lintels made by a concrete firm ted and they told me i couldnt use them till 7 days after manafacture.
i dont think rain water is any kind of problem for dry concrete though is it?
regards LLL ???
Posted: Tue Jul 24, 2007 8:52 am
by Phil H
Thanks guys for your input. I just imagined all the pools of water sitting on the top would not help anything. I imagine looking at the side views of the slab that it was still quite damp undeneath, the slab is some 15 inches thick max. No doubt when the concrete building is up and secured condensation may well form for sometime inside. Would i be better using a Dehumidifier to help the drying out process or just leave alone for as long as possible.
Posted: Tue Jul 24, 2007 7:44 pm
by matt h
try using blowers in combination with dehumidifiers, as speeds up removal of excess moisture. will you be screeding over?
Posted: Tue Jul 24, 2007 7:51 pm
by matt h
If you experience condensation try using blowers in combination with dehumidifiers, as speeds up removal of excess moisture. will you be screeding over? Laying of floor leveling compounds often increases condensation formation until fully cured, so ensure there is adequate airflow.:rock:
Posted: Tue Jul 24, 2007 8:08 pm
by Ted
lutonlagerlout wrote:i had some lintels made by a concrete firm ted and they told me i couldnt use them till 7 days after manafacture.
i dont think rain water is any kind of problem for dry concrete though is it?
regards LLL ???
I think you only have to wait longer than a week if making something like a dam!
I don't think rainwater is a problem normally once it has hardened.
Posted: Tue Jul 24, 2007 10:20 pm
by lutonlagerlout
from what i heard ted there is crete in the hoover dam that hasn't set yet ,they were pouring that fast
and i quote wikipedia
The first concrete was placed into the dam on June 6, 1933. Since no structure the magnitude of Hoover Dam had been constructed, many of the procedures used in construction of the dam were untried. Since concrete heats up and contracts as it cures un-even cooling and contraction of the concrete posed a serious problem. The Bureau of Reclamation engineers calculated that if the dam were built in a single continuous pour, the concrete would have taken 125 years to cool to ambient temperature. The resulting stresses would have caused the dam to crack and crumble.[4] To solve this problem the dam was built in a series of interlocking trapezoidal columns. Each pour was no more than 6-inches deep. Because of this depth it is extremely unlikely that construction workers were accidentally buried alive in the concrete, contrary to popular folklore.[5]. To further cool the concrete each form contained cooling coils of 1 inch (25.4 mm) thin-walled steel pipe. River water was circulated through these pipes to help dissipate the heat from the curing concrete. After this chilled water from a refrigeration plant on the lower cofferdam was circulated through the coils to further cool the concrete. After each layer had sufficiently cooled the cooling coils were cut off and pressure grouted by pneumatic grout guns. The concrete is still curing and gaining in strength as time goes on.[6]
There is enough concrete in the dam to pave a two-lane highway from San Francisco to New York [7].
regards LLL
Posted: Wed Jul 25, 2007 11:35 am
by Ted
Someone told me about a dam on Megastructures once but I didn't see it...
This is from Portland Cement Association:
What does 28 -day strength mean?
Concrete hardens and gains strength as it hydrates. The hydration process continues over a long period of time. It happens rapidly at first and slows down as time goes by. To measure the ultimate strength of concrete would require a wait of several years. This would be impractical, so a time period of 28 days was selected by specification writing authorities as the age that all concrete should be tested. At this age, a substantial percentage of the hydration has taken place.
http://www.cement.org/basics/concretebasics_faqs.asp