Concrete Separation
Concrete Separation
(OP)
What is the height limit concrete can be dropped (or poured) before separation of the granular occurs. I’ve heard a few differing opinions on this subject, and was just wondering what the consensus was.
Thanks,
Laura
Thanks,
Laura





RE: Concrete Separation
The classic geotechnical application where this discussion arises is the construction of drilled shafts.
In FHWA IF-99-025 "Drilled Shafts - Construction Procedures and Design Methods", the O'Neil and Reese conclude that concrete may be placed by free fall for distances of
"up to about 24.4m (80 ft) without problem as long as the concrete does not strike the cage or the borehole wall." - p.200
This, according to the text, is based on a small number of test shafts where the concrete was sampled and tested after shaft construction. The deepest shaft tested was 80 ft deep.
I suspect that the distance may actually be greater than 80 ft, but not too many drilled shafts are constructed deeper than this.
The Portland Cement Association (PCA) or ADSC may have further/other information on this subject.
Hope this helps,
Jeff
Jeffrey T. Donville, PE
TTL Associates, Inc.
www.ttlassoc.com
RE: Concrete Separation
RE: Concrete Separation
www.SlideRuleEra.net
RE: Concrete Separation
We caught a contractor placing concrete with heavy renforcement (bundles of #8 rebar, etc) in 4 foot diameter piles for a landslide mitigation where he dropped concrete 75 feet (against our recommendation of no more than 5 feet). We actually cored the middle of a couple piles and drilled a couple pilot holes where we cored laterally.
Much to our surprise we found no honeycombing, especially in the outer raches where we expected to see signs of voids or disaggregation.
Regardless we would never recommend such a practice with rebar cages, but it was interesting to see.