Plywood for concrete forms

Industrial Toys · Dec 13, 2017

So, is there an ideal ambient temperature for small pours? Is concrete strength affected if poured in cold temps above freezing?

Streetcar · Dec 13, 2017

I have not researched maximum temperatures, but precast manufacturer will steam cure concrete members

Larry Caldwell · Dec 13, 2017

/pine said:
Actually, the amount of water/Portland cement is relative to the required slump for the application (job) and workability...not just the end result strength of the pour...Good luck getting a stiff mix (high slump) into intricate forms or through a concrete pump etc...

A concrete pumper is a whole other mess. If you are pumping a high pour, the pumper has to develop huge pressures. This drives water into the aggregate, so you can feed a 4" slump into the pump, but a 2" slump comes out of the hose 50 feet up. This can result in heated discussions between the concrete finishers, who insist that a 2" slump is not workable and the materials inspector who insists that adding water on site will ruin the batch design. The batch plant can add pozzolans to improve workability, but there are limits to how much that helps a stiff batch.

Larry Caldwell · Dec 13, 2017

Industrial Toys said:
So, is there an ideal ambient temperature for small pours? Is concrete strength affected if poured in cold temps above freezing?

My idea of a perfect day for flatwork is 50 degrees. Concrete curing is an exothermic process. When they built Grand Coulee they had to embed cooling pipes in the dam to keep the concrete from boiling. If concrete freezes before it cures it will ruin the concrete, and flatwork is most susceptible because it is thin with a lot of exposed surface. The batch plant can add calcium chloride as an antifreeze that will give a little protection, but you can't add very much without ruining the strength of the concrete. The plant also sometimes batches with hot water, which gives the cure a running start. In hot weather, a batch plant will batch with ice to cool the mix. In hot weather it's common to keep a sprinkler going and in cold (sub-freezing) weather it's common to cover and even heat the forms.

Snobdds · Dec 13, 2017

Larry Caldwell said:
If you keep it moist, concrete will continue to cure for 50 years. It reaches 90% of design strength in about 28 days. After that curing slows down. If it loses moisture, curing stops.

I think you should search a couple of terms...

Hydrophobic concrete
Hydroscopic concrete

:thumbsup:

Larry Caldwell · Dec 13, 2017

Snobdds said:
I think you should search a couple of terms...

Hydrophobic concrete
Hydroscopic concrete

:thumbsup:

Rest assured, I'm an ACI certified concrete inspector. You are just confusing yourself.

/pine · Dec 13, 2017

Larry Caldwell said:
A concrete pumper is a whole other mess. If you are pumping a high pour, the pumper has to develop huge pressures. This drives water into the aggregate, so you can feed a 4" slump into the pump, but a 2" slump comes out of the hose 50 feet up. This can result in heated discussions between the concrete finishers, who insist that a 2" slump is not workable and the materials inspector who insists that adding water on site will ruin the batch design. The batch plant can add pozzolans to improve workability, but there are limits to how much that helps a stiff batch.

Somewhere I still have the ASTM manuals for procuring, testing and documenting test cylinders...they were on a required book list for a comprehensive class A GC's lic. in FL (circa 1970) they dictate from where and when test cylinders are to be taken as well as slump tests...