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RE: Fiber-reinforced concrete (was: Control joints in elevated sl abs)

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I have responded to Mike and Bob off line for one simple reason.  One of the
manufacturers of plolypropylene fibers has a token staff of inept concrete
mix design "experts", but they retain a very aggressive and callous legal
staff.  I am too old to get embroiled in a major law suit by posting my
unedited response to the list.  Please understand.

However, I will post my own personal edited experience.

Bear in mind that polypropylene fibers do not alter the rate of concrete
shrinkage.  And if polypropylene fibers CAN NOT be used for flexural
resistance (as stated in the product literature), how do those little fibers
understand what is tensile stress due to shrinkage and what tensile stress
is due to flexure?  They can't and the concrete cracks.

Bob,

Unreinforced concrete is a different issue, and yes there are tons of
projects with unreinforced concrete.  I have designed tons of unreinforced
paving and dams with nary a rebar.  The problem is when you think that
polypropylene fibers in concrete is reinforced even to the extent of
shrinkage steel.

And again, I have used polypropylene fibers in shot crete, but only to
reduce rebound, and then the add rate was about 5 times higher than the
manufacturer recommended.  But it worked well.


Mike,

I, personally, have had VERY bad and expensive experience with polypropylene
fibers.  

Project 1: On one job (slab on steel deck (non-composite), bar joists, etc.)
I was the forensic engineer.  There were indeed fewer cracks, but the cracks
were significantly larger to the point where aggregate interlock was lost.
Differential curling resulted to the point where tripping hazards were
created.  Epoxy injection at $5.00 per foot was required.

Project No. 2.  The contractor requested substitution of fibers for the WWF.
The engineer said no.  The architect said OK.  The contractor put in the
fibers, and pulled the WWF.  The result was the same - fewer, but bigger and
wider cracks that became trippers due to the differential curling and loss
of aggregate interlock.  The entire slab was covered with a resilient
covering that would hide most cracks, but not these big canyons.  Big law
suit, various people took a financial hit.  The facility was shut down, and
the entire slab was replaced with enough rebar to build Watertower Place.
(once bitten 10 times shy)

No.  I do not use fibers except in shot crete, but my add rate is very high,
and I use it to reduce rebound.

If this results in a legal action, will SEAINT create a legal defense fund
for me, or do I turn into the fugitive engineer?  

Regards,
Harold O. Sprague


> -----Original Message-----
> From:	bob.ross(--nospam--at)wgint.com [SMTP:bob.ross(--nospam--at)wgint.com]
> Sent:	Friday, November 30, 2001 10:46 AM
> To:	seaint(--nospam--at)seaint.org
> Subject:	RE: Fiber-reinforced concrete (was: Control joints in
> elevated slabs)
> 
> OK Harold:
>    The California Department of Water Resources has about
> 400 miles or more of 4-inch concrete lined (paved) open
> channels. This has served the State very well for 20 to 30
> years without any steel.
>    These canals transverse the coastal range including
> regions of landslides, thrust blocks, quicksand, holes,
> faults, rock, mud, springs, and whatever else the geologist
> may encounter through that career choice.
>    During emergency liner repair these were cleaned,
> re-leveled, covered with a waterproofing membrane, and then
> covered with 2-inches of 4,500 psi shotcreted mixture with
> roller screeding for consolidation. Some of this cover
> mixture included  polypropylene fibers.
>    Those panels that did not have the polypropylene fibers
> demonstrated shrinkage cracking outside of the crack control
> joints, which were located over existing control joints.
> Where the polypropylene fibers were used the crack control
> joints appeared to serve their purpose. These joints were
> sealed with
>    No reinforcing steel was installed due to the
> availability of moisture.
>    The 2-inches of concrete cover is an anchor and an
> abrasive resistance surface to the "potable" water delivered
> from the "biomass" of the Sacramento Delta region.
> 
> -----Original Message-----
> From: Michael Hemstad [mailto:mlhemstad(--nospam--at)yahoo.com]
> Sent: Friday, November 30, 2001 8:21 AM
> To: seaint(--nospam--at)seaint.org
> Subject: Fiber-reinforced concrete (was: Control joints in
> elevated
> slabs)
> 
> 
> >... cracking in concrete slabs on metal deck is an
> issue.
> >
> >Number one, never use polypropylene fibers.  Use mesh
> or rebar.  This
> is
> >another topic.
> 
> OK, Harold, you opened this can.  Tell us about
> polypropylene fibers.
> 
> I've got a bunch of outdoor slabs on grade (not
> elevated slabs-I changed the subject) that I pulled
> all the steel out of due to concerns about de-icing
> salts.  In the slabs I put poly fibers.  The slabs
> have substantial edge beams which I couldn't make
> myself believe would be all right without steel, so I
> used epoxy bars.  Good, bad, or indifferent?
> 
> Mike Hemstad
> TKDA
> St. Paul, Minnesota
> 
> 

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