Self compacting concrete 1

[apetr26542]

The contractor is proposing to use "Agilia" for some round columns in a smooth form. The reason is to reduce costs for finishing as these will be exposed. I've never specified this concrete and the submittal does not give the design mix because it is a trade marked product. Only gives the compressive strengths. Pros? Cons? Weathering capabilities?

 

[discopants]

it will produce excellent concrete but that is just a brand name, every admix company will produce their own self compacting admixture. Used one recently and the only complaint from the contractor was the strengths were too high when he had to break some out.60kn+ when he only asked for 40 !

 

[SirAl]

The contractor must ensure that the formwork is tight and fairly well sealed. This stuff flows like water.

 

[DTGT2002]

The formwork must be designed for what is essentially a full liquid head.

The quality control must be monitored by the concrete company as testing slump is impossible, the test sees how far the mix spreads.

The results can be great when all is prepared well - formwork, concrete, etc.

You should still be able to see historical data or some sort.

Perhaps the local Blue Circle (LaFarge) rep could come to your office an do a presentation on the product?

The concept as I see it is that Agilia is a process not just a mix name. On the way to produce the self compacting product, the quality control standards are ratcheted up, and this produces a better product.

The contractor should be willing to entertain a meeting with the concrete rep to thouroughly discuss your questions and allow you to make the decision if this is an adequate product for your requirements.

Good luck!

Daniel Toon

 

[daddycool]

I don't agree with the statement that formwork should be designed for full liquid head. Normal concrete formwork pressures are higher due to the action of vibrator compaction. Compacting with a vibrator reduces concrete yield value to zero, whereas SCC always posesses some sort of yield (no matter how small). Therefore, pressures on the form will be higher for normal concrete. There is also imposed pressure stresses from the waves provided by the vibrator. It seems that the gretaest pressure imposed from SCC is when the concrete is first dropped into the form.

 

[DTGT2002]

The capacity of a vertical form, such as that of a wall form or column form must be sufficient to contain the pressure exerted by the liquid head of the concrete.

Agilia and other self consolidating concrete mixes are placed into the formwork in a far more liquid state than any "normal" structural concrete I have ever seen.

On a micro scale, "normal" concrete placed and vibrated in place will certainly show full liquid properties at the point of vibration. "Normal" concrete is also placed in lifts, ideally prescibed heights per hour and at worst limited by what human labor can allow. Agilia can be placed as rapidly as the placement method allows. Rather than localized areas of liquid behavior, the effacts of retaining a 150 pcf liquid would be seen throughout the form.

Conventional formwork designs dictate an allowable placement rate of concrete for a given temperature, varied based on admixtures and other historical factors. With time, the concrete first placed will no longer behave as a true fluid, thus the allowable pour rate.

Formwork should always be designed appropriate for the situtation. Forms intended for use with "normal" concrete may not be adequate when used with Agilia.

And as stated above, construction tolerances acceptable with normal concrete may lead to blowouts and loss of concrete wehn used with a mix a free flowing as Agilia.

That said, Agilia is really an amazing product, something useful that we will get used to and get much use out of.

Regards,

Daniel