Monday, September 2, 2013

Concrete Filling Drilled Caissons - Don't just let the concrete fall

Filling drilled caissons with concrete - do not just let the concrete fall!

Free Fall

Recently, I was asked to weigh in on a project where the methods for placing concrete into drilled caissons were under debate.  

The concrete contractor insisted that the concrete could be dropped from the surface down into the 40 foot hole.  The swimming pool contractor did not feel comfortable with that, but did not know of any standards that dictated otherwise.

American Concrete Institute (ACI)

The ACI publishes a myriad of concrete standards.  Most issues regarding concrete, are discussed in their standard ACI 318.  ACI 318 has been adopted and incorporated into the International Building Code (IBC) as well as the California Building Code (CBC).  The IBC is the basis for building codes relating to concrete, that have been adopted across the nation.

ACI 318 states that concrete should be placed as close to it's intended location as possible.  So, in the case of drilled caissons, that means filling the hole from the bottom up.  The weight of 40 feet of 3-4" concrete filled hose is unwielding.  Usually a crane, backhoe or concrete boom is required to fill such deep holes.

California Building Code

The CBC is a little more compromising.  It allows for the concrete to fall no more than 6 feet.


Why is there any concern at all?  Separation.

If the concrete is allowed to fall a significant distance, the aggregate separates from the concrete.  A homogenous mix is not delivered to the final resting place.  Pumping the concrete from 40 feet also allows the concrete to bounce off of the reinforcing steel, also separating the aggregate from the cement.

To ensure that the specified mix design is delivered as specified, precise placement practices are critical.  

Contact the author, Paolo Benedetti of Aquatic Technology Pool and Spa at: or 408-776-8220. 
Visit his website at: 
All Contents © Aquatic Technology Pool & Spa, 2013. 
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To contact the author, Paolo Benedetti of Aquatic Technology pool and Spa, email him at: or call 408-776-8220.
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