Expert: Dan Griffin - 8/23/2008

Question
Question about partial casting of footing.
Sir ,

I want to know about old & new casting bond in isolated footing. A 6 storied apartment building designed (structural) by me. One of the footing size 13’ * 13’-9”*23” & depth of footing 8’ from existing plinth level. Bottom  reinforcement bar 16 mm dia@5” c/c both way (no top reinforcement in footing ).column size =12”*20” below plinth(10”*18” above plinth level). Rebar =16-20mm bar. Ultimate column loading=450 kip. Bearing capacity of soil is 2.75 ksf .(Accidentally my site engineer cast 14” tapered part at a time (surface was rough) after three days later rest of 9” cast .Rest casting was done by cleaning surface & grouted cement . Do u think the bond for shear is o.k. Do u think additional rebar was required for joint between old & new bonding. Please suggest me for the interior footing casting .


Answer
ahsanul,  I really don't feel qualified to answer your question.  It is standard practice to use neat grout when bonding a fresh concrete lift.  The thing that worries me is that the new concrete lift was only 9", I assume you are quite assured as to the concrete quality and I feel that everything should be fine, but I would prefer that you get another opinion from a structural specialist with a specialty in concrete design and execution.  I would like you to contact the Concrete NEtwork or the Concrete Construction Magazine:
http://www.concretenetwork.com/press/contact-us/
OR
http://www.concreteconstruction.net/magazines/contact-editors.asp?sectionID=701#...

I would call them rather than write if time is critical.  If they do not have someone able to answer, they should be able to get you in touch with someone who does.

I would like to hear what the solution is.