cubic strength to cylinder strength

huangyhg

cubic strength to cylinder strength
hi all
does anyone know exact formula to convert cubic conc. strength to cylindrical strength?
normally i use 0.8* cubic strength after 28 days

i use this formula fbk=(fck-1.77)/0.83...[mpa]
fbk...cubic conc. strength
fck...cylindrical strength
drile007
seem your equation give higher values than the one i used
which is fcy=0.8fcubic?
what is the reference of your formula?
basically you use 0.8xcubic to get cylinder.  seems to be the standard for most.  neville and brooks ("concrete technology") indicates that this is so.  however, there is evidence that the actual factor depends on the strength of the concrete and moisture condition of the specimens.  i think that the uk standards has actual factors for the various strengths of concrete - and i've seen a table in an indian concrete book to justify this.  this has been discussed several times in the past so do a search on the site for previous threads. (about 2 years ago, if i re  
the draft ec2 that i have lists these cylinder/cube strength classes:
c16/20, c20/25, c25/30, c30/37, c35/45, c40/50, c45/55, c50/60
average factor is about 0.8.