Plywood for concrete forms

[SPYDERLK]

Man, this got stupid

Yeah.​

If you actually want to know something about it that is correct, ask Rock Knocker a question.​

/pine your post is misleading as it leaves out the first part of the discussion of the water needed for the chemical reaction. Your post is about the excess water remaining in the concrete

Yea, it isn't a very good blog. The fact that cement is a hydrated compound that incorporates water (or OH) in it's structure. There may be excess water in the pour, more likely with lazy finishers without a design mix. A modern high strength design mix may actually have close to zero excess water.

:laughing:
You mean like:??:laughing:

There may be excess water in the pour, more likely with lazy finishers without a design mix. A modern high strength design mix may actually have close to zero excess water.

The water/cement ratio (design mix) has to be adjusted for the amount of excess water required for applicable "workability" modern design mixes state a minimum and maximum slump...

Good luck placing a conc. mix (that only has enough water required for the hydration of the cement) in a form and around multiple rebars etc....

So you had an answer and didnt need to ask a question.

Well, good.​

 

[Streetcar]

Industrial toys
You are correct in forms are easier to clean and reuse if pulled early. Concrete is also easier to patch if green.
Forms will provide some protection against freezing of concrete.
Structurally there are few reasons to pull forms off concrete. Deterioration of forms being only one I can currently think of

 

[Streetcar]

Eddie
Do you have adjustable scaffolding you can use to support your roof forms. Or you could use 4x4 post set on horizontal sill plate

 

[Larry Caldwell]

No, it's a chemical reaction between the Portland and the lime. Water just keeps the chemical reaction, Cure, to a slower rate. There is no such thing as hydrating in concrete...

Yep. The strongest concrete comes from just dumping bags of dry concrete mix into the forms. It's already dry, so you can strip the forms as soon as they are full.

 

[Larry Caldwell]

Hydrating is to always put water into something. Concrete "hydrates" once at the initial stage, then there is no more hydrating.

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.

 

[Larry Caldwell]

So yea...portland, lime and water.

What point here are you making?

You are thinking mortar, not concrete. Portland cement is a mix of kilned limestone, fly ash, and other materials. Concrete is made by mixing Portland cement with graded aggregate. Mortar is made by mixing Portland cement with lime and sand.

 

[Industrial Toys]

I have always been a bit confused about curing concrete. It's an isothermic (sp?) reaction. It gives off heat when curing. In the hoover dam they piped through cold water so the concrete would cure. Yet in cold weather, my concrete has taken very long time to harden. You would think, that would hasten the process, not slow it down.

 

[Streetcar]

Curing of concrete is exothermic( released heat) .the water is pumped through the concrete to remove excess heat . If there is a large difference between the interior and exterior temperatures the concrete can crack from thermal stress. In large concrete pours this can be a problem.

 

[Industrial Toys]

The documentary I saw years ago, I believe, said that the concrete might never cure had it not been for this cooling measure.

 

[Streetcar]

Industrial toys
The cooling measures allowed the concrete to be placed sooner adjacent previously placed concrete. Theoretically concrete will continue to gain strength as long as water is available for continued hydration. 99 percent of ultimate strength is reached within 56 days in most concrete

 

[Industrial Toys]

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

 

[Streetcar]

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

 

[Larry Caldwell]

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]

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]

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]

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]

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...

 

[Snobdds]

It explained what I said, if you noticed...

Aren't well all experts here...?

 

[MossRoad]

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

Ouch! :laughing:

 

[MossRoad]