USE OF SELF CONSOLIDATING CONCRETE IN ACIP PILES

[Gosha]

I know that some research has been done by Michael O'Neil regarding the use of self-consolidating concrete in drilled shafts.

My question is whether somebody knows about the use of SCC in Augered Cast-in-Place piles.

 

[civilperson]

Totally appropriate use but over-kill. Regular concrete falling in the shaft will segregate and recombine to have a dependable mix with the last few feet available to stingers for consolidation. Or use of tremie or elephant trunk to keep the free fall less than 5 feet is another way to assure no segregation.

 

[civilperson]

In collapsing sands, the concrete is pumped down through the auger during raising of the auger flights and at conclusion of the concrete placement the reinforcing cage is inserted.

 

[BigHarvey]

Bad idea for , particularly if you have to insert a reinforcement cage in the pile. You need to keep the rheological characteristics of you concrete constant if you want to be able to lower the reinforcement in the pile once it is cast : ie maintain a slump value of 7 to 8 inches.

 

[Zambo]

How deep is the pile?

I assume you will excavate the pile using bentonite or polymer as excavation support. Then you will lower the reinforcing steel cage into the excavation. You would then use a tremie to concrete from the base up displacing the bentonite/polymer as you go. The concrete would normally have a slump of 200-250mm.

I've never seen reinforcing steel lowered into a structure after concreting - sounds risky.

 

[Speedycrete]

I have video of this type of pile being drilled and the grout being pumped in. My flash player isn't installing correctly, I haven't been able to preview it, so I'm not sure if the video includes a shot of the rebar cage being lowered into the grout.

http://s67.photobucket.com/albums/h...on=view&current=AugerCastPileRig-Drilling.flv

http://s67.photobucket.com/albums/h...ion=view&current=AugerCastPileRig-Pumping.flv

 

[franksa]

The "Free-Fall" research was done in the US in the 70s. They concluded that free-fall was better than using a chute.

My experience of free-fall is it's ok at ANY depth. It doesn't segregate, but separates into blobs. On impact there is a terrific vibration effect. Full-length cores of the piles show good quality concrete. I have done cores on 3 jobs to convince the client's engineer.

Normal slump (80mm) needs vibration. 110 mm does not, except for the top few metres, where the impact effect is less.

A slump of 220 mm is self-compacting, if the mix is good. It must not be vibrated, or the coarse aggregate settles out.

Consulting engineers can take a lot to convince them it's ok. Of course the stream of concrete should be centralised. Best done by a good operator with a shovel. You listen for the "plop plop" sound as it hits the bottom. However a funnel with a 500mm tube sitting central in the reo cage is ok too. It's more trouble, needs a crane, but the consulting engineer is more likely to approve the method.