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RE: fibers

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Andrew,

My worst nightmares have been with fixing the slabs that use polypropylene fibers. Rebar and WWR cover up a lot of sins because they hold the cracks together and you won't loose aggregate interlock. The biggest sins are not accurately predicting how a slab will shrink and making proper accommodations.

Steel fibers are a much different animal, but a practitioner still needs to understand how the slab will shrink and crack in order to place the right joints in the right locations, at the right time.

I will not use polypropylene fibers, but I will consider steel fibers. If I use steel fibers, I detail everything and I require: a preconstruction meeting between all of the contractors (GC, finishers, concrete supplier, fiber supplier, admixture supplier, pumping contractor, materials testing company, special inspector, etc.) and a test placement of the proposed mix at the elevation the pumps will need (the pump and line height make a big difference).

Regards,
Harold Sprague

From: "Andrew Kester" <akester(--nospam--at)bbma.com>
Reply-To: <seaint(--nospam--at)seaint.org>
To: <seaint(--nospam--at)seaint.org>
Subject: fibers
Date: Thu, 21 Oct 2004 09:35:03 -0400

FWIW, we spec fibers all of the time, and have had a lot of good experiences with them. We had one of the fiber manufacturers do a presentation and they have programs and formulas for placing them in flexural SOG like warehouses with racks. The big thing to remember is DOSEAGE and slab thickness. In those types of applications you may need 35+ lb/cy of STEEL fibers, not the usual 2-3lb/cy of polypropolene like in SOG for spider crack control. Will they keep a large crack from opening up like conventional reinforcement? Maybe not.....

BUT, before you write fibers off completely, I suggest taking another look at what the manufacturers are reccomending now, and maybe have them come do a lunch presentation at your office so you can ask them questions and make an informed decision. And I am in no way affiliated with any fiber company...

Andrew Kester, PE
Longwood, FL


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