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RE: cantilver conc balcony

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Paul,
 
Anything you place in a joint will require inspection and periodic maintenance.  Anything requiring periodic maintenance will likely be ignored. 
 
I would suggest post tensioning using bonded encapsulated strand.  You can design the top concrete to be in compression and the strand would be protected from corrosion by the encapsulation.  I do not like to rely on admixtures for corrosion resistance.  If you want a more definitive mix for corrosion resistance, consider using SCC. 
http://www.selfconsolidatingconcrete.org/
 
You will get very low w/c ratios and high strength.  As a minimum use epoxy coated rebar. 
 
This is a site for bonded encapsulated strand by VSL. 
http://www.vsl.net/SYSTEMSPRODUCTS/VSLABBONDEDSLABS/tabid/90/Default.aspx
 
You might also consider a ribbed structure like joist or skip joist to reduce weight and increase stiffness.  A post tensioned ribbed structure might be your best bet.  I would still urge you to consider the bonded PT.  Call the PTI.  http://www.post-tensioning.org/  They can give you sound advice and help with a preliminary design. 

Regards, Harold Sprague
 

From: PFFEI(--nospam--at)aol.com
Date: Fri, 14 Oct 2011 09:04:40 -0400
Subject: cantilver conc balcony
To: seaint(--nospam--at)seaint.org

I have an exterior concrete balcony with a 15' cantilever and 10' backspan.  I expect that no matter how thick I make slab I will get deflection and a crack over the support.  would it be best to detail a pour joint over the support or cut a crack control joint to control the crack?  joint could be filled with caulk / flexible joint sealer.
 
Also, project is located on a bluff about 1/2 mile away and 300' above the ocean (Malibu).  For slab exposed as finish, is anything recommend fro rebar protection?  I was thinking 4000 psi conc with w/c = 0.5 max, and 2" cover.  should I include something like xypex in the mix, or increase rebar cover, or am I distant enough from ocean that salt will be a minor issue?
 
Thanks in advance,
 
Paul Franceschi