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RE: Fibers in Composite Slab

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ANSI/SDI-C1.0 Standard for composite steel floor deck (2007) now allows
the substitution of steel fibers meeting ASTM A820 at a minimum dosage
rate of 25lb/cy or macro (as opposed to micro) synthetic fiber of
polyolefin with an equivalent diameter of between .4 and 1.25mm with a
min aspect ratio of 50 at a dosage rate of 4lb/cy
This only replaces temp-shrink so any negative reinforcing over the
girders, or reentrant corner bars would still be needed.
I seem to recall something relating to the synthetic fibers and
fire-rating still not having been tested/resolved the last time I
looked, but that work may be complete by now.
I commonly allow the option to substitute a blend of Steel fibers with a
micro synthetic fiber (such as Novomesh 850) for the WWF but
surprisingly few even consider that option until we really start pushing
that the wwf must be chaired into position.  I was reasonably pleased
with one project that did use the steel fibers (with additional mild
steel for corners and girders).  There did seem to be a little more
issue with crack width at reentrant corners but I am not wholly
convinced the corner bars were consistently installed prior to the pour.
There seemed to be a little more frequent, but tight, cracks on the
surface but since all of the area was to be under tile or carpet this
was not a concern in our case.  I think the real benefits come in safety
(walking on properly chaired WWF is nearly impossible) and the notion
that the reinforcing is throughout the cross-section, instead of hoping
that the WWF winds up in the right place. 
I just had a second composite one placed with the steel fiber blend last
week, but have not gotten by to get a look at it yet. I have not tried
specifying one using just synthetic macro fibers or a fully synthetic
blend.

Despite their initial concerns on the first one about finishing, I did
not hear that any problems occurred and there was nothing apparent on
the surface.  This goes for using them in slab-on-grade as well which I
have seen more of.


Michelle Motchos, PE
Stevens & Wilkinson of South Carolina, Inc.
Columbia, SC 

-----Original Message-----
From: Adam Vakiener [mailto:avakiener(--nospam--at)southernae.com] 
Sent: Friday, July 11, 2008 7:18 AM
To: SEAINT
Subject: RE: Fibers in Composite Slab

Does anybody out there have any experience with using fiber
reinforcement in an elevated composite slab?  We've got a project that
has come in way over budget, and the contractor has suggested that we
could save some money by taking out the welded wire fabric and just
using fibers.  Given the situation, we'd like to entertain the thought,
but none of us here have done it, so we don't have any comfort level
with it and aren't particularly thrilled to have this $100 million
project as the test case.

If you've tried this, did you use synthetic fibers, steel fibers, or a
mixture?  How were the results?  Were there finishing problems?
Cracking?  If we go with fiber, we're planning on keeping rebar over the
girders to control cracking in the negative moment region - would you
agree that this is good practice?  Any other considerations?

Thanks.

-- Joel


 

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