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RE: Fibers in Composite Slab[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: <seaint(--nospam--at)seaint.org>
- Subject: RE: Fibers in Composite Slab
- From: Harold Sprague <spraguehope(--nospam--at)hotmail.com>
- Date: Fri, 11 Jul 2008 17:28:14 +0000
I would consider using steel fibers on a slab on deck or slab on grade in lieu of synthetic fibers, but I would insist on a test placement before I would recommend it on a large scale placement. There is a learning curve. Steel fiber concrete batches differently and pumps differently. I agree that concrete finishers will not have a problem once they gain familiarity. |
But it will not result in a big savings especially if there is a lack of familiarity. Any hard bids will have a familiarity factor. No one wants to be surprised.
I would advise a test pour, and a preconstruction meeting to include all of the stake holders including the vendors, ready mix provider, finisher, testing lab, special inspectors, etc. I would also suggest that you consider belt conveyors as opposed to pumps.
A lot of ready mix companies are carrying belt conveyors on their trucks. They do not need to prime with grout, and the mix is placed without changes like air content. (Overhead pumping can reduce the air content and slump depending on the height and angle of the boom.)
I would also request that a vibrating screed like a Copperhead be used in lieu of hand rodding.
> Subject: RE: Fibers in Composite Slab
> Date: Fri, 11 Jul 2008 08:51:49 -0400
> From: mmotchos(--nospam--at)sw-sc.com
> To: seaint(--nospam--at)seaint.org
> 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
> 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?
> -- Joel
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