Answered Question regarding column pouring height

DEEPAK Tewatiya

Junior Member
Dec 1, 2017
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Jhansi
Dear all Senior/Junior
As per IS Code-456 maximum free fall of concrete not more than 1.5M, but as I have seen and also using pouring farma at site 2.4M Height. Please give your feedback.
Thanks
 

amd007

Active Member
Premium Member
Apr 17, 2018
198
273
mumbai
For walls and columns (i.e. deep, narrow forms), problems occur when the concrete is dropped from too great a height and ricochets off the reinforcement and form-faces, resulting in segregation. The means of avoiding this vary with the type of distribution equipment being used please see diagram:

screenshot-civilblog.org-2019.12.17-12_50_00.png

You can also create a window at 1.5m height and first concrete the column up to 1.5m close the window and then concrete the balance height up to 2.4m, this is one of the best way to concrete a column/ wall without any segregation.

You can adopt any method illustrated above as long as there is no segregation of the concrete.
 

amd007

Active Member
Premium Member
Apr 17, 2018
198
273
mumbai
Thanks sir,
can you share any book/code , where i can get these type knowledge..
You are now at the right place to raise your queries on this forum, you will get all your queries resolved.;). A lot of learned and vastly experienced people are in this group who will surely try to help you out. Good luck and Cheers.
 
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Dnyan Deshmukh

Eternal Member
Staff member
Sep 7, 2017
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4,293
Pune
While reading IS code, we should read it carefully to understand what does it mean.

It states - as a general guidance, the maximum permissible free fall of concrete may be taken as a 1.5 meter.

it does not say you should consider as same but in absence of data, you may take this.

IS codes do cover all aspects of the construction and those are made to be practically applicable for even construction of single house to a mass housing projects.

Back in time i saw something special about free fall height, just did search and pasting lines from search on google.

As published in Concrete International, a publication of the American Concrete Institute

Sometimes specifiers and inspectors dictate the maximum free-fall distance of concrete because they believe limiting free fall is necessary to minimize concrete segregation. Usually they limit the free-fall distance to 3 to 5 ft (0.9 to 1.5 m), but occasionally the limit is as little as 2 ft (0.6 m). Neither ACI 301- 99, “Specifications for Structural Concrete,” nor ACI 318-02, “Building Code Requirements for Structural Concrete,” limit the maximum distance concrete can free fall. ACI 304R-00, “Guide for Measuring, Mixing, Transporting, and Placing Concrete,” states that “if forms are sufficiently open and clear so that the concrete is not disturbed in a vertical fall into place, direct discharge without the use of hoppers, trunks, or chutes is favorable.” ACI 301, 304, and 318, however, all require placing the concrete at or near its final position to avoid segregation due to flowing.

In 1999, the Federal Highway Administration eliminated its 25 ft (8 m) free-fall limitation and now allows unlimited free fall of concrete. Free fall of concrete from heights of up to 150 ft (46 m), directly over reinforcement or at high slumps, does not cause segregation or reduce compressive strength. Restricting free-fall heights does decrease concrete production rates, which increases owners’ costs without increasing concrete quality.


Hopefully now your question would have got one more aspect to think on what should be free fall height of concrete.

I personally do pouring of concrete from height of 2.4 meter.

For heights like 4.2 meters, we initially used tremie pipe for casting of walls and columns but later on we also made window in form to facilitate the work. (at this project we had concrete boom pacer and cranes to do this job).
 

HockeyPuck

Active Member
Feb 3, 2019
106
81
Chicago, Illinois (USA)
DEEPAK Tewatiya Realizing that Civil4M membership comes from all corners of the globe, our Q&A's often-times can provide different perspectives on engineering and construction applications - Your question fits that mold.

One key determinant of allowable concrete fall heights is what the mix will (or will not....) hit on the way down. Here in the US, and specifically in the State of Illinois where I do the majority of my work, our state's drilled shaft specifications allow for as much as 60' of concrete free fall. I know that sounds like a lot, but as the term "free fall" operatively states, it can only be used when, during concrete placement, the mix has no chance of hitting the reinforcing cage, sidewalls, forms, casings, etc. on the way down - If it does, or has the possibility of hitting anything during the fall, it cannot be installed in this manner without using a tremie, drop chute or pump.

We typically use what we know as a Drilled Shaft Mix (DS), which basically uses a top-sized aggregate of 3/8" chips making the mix more-fluid & viscous for concrete placement. It is pretty rare that we find ourselves in such pristine shaft conditions where we can use simply back a concrete truck up to the shaft excavation and dump the concrete in the hole: The presence of groundwater in the shaft or loose soil column conditions (collapsing walls) most-often require the use of slurry to maintain the excavation or temporary casings. With groundwater or slurry, a tremie must be used to keep the point of concrete placement below the water/slurry line to preserve concrete integrity, of course. Not to mention that just about all concrete structures we build have some sort of rebar in them....

This is only one case: You'll certainly want to check your job specifications and code requirements to determine what is permissible for your installation - Cheers!!

 
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