huangyhg

pumping fiber reinforced concrete
a structure we did requires 120 lbs. steel fiber reinforcing per cubic yard of concrete. the concrete has to be pumped, but the contractor tried one section and said the fibers were clumping up and was not able to be effectively pumped. he is using the largest pump hose he can get. any suggestions to what could be done to get this to work?

just brainstorming, some possibile alternatives are:
different style of steel fiber
different size or size mix of steel fiber
fiberglass (or some other material) fiber
find a different way to transport the steel fiber to the final location
bigger pump
different style of pump
probably your best bet is to contact the manufacturer of the steel fibers.
get rid of the steel fibers and replace with standard deformed rebars in top and bottom grids.
agree with civilperson.
steel fibres have caused lots of problems on many jobs and many court cases are now on foot. i would stay with conventional reinforced concret.
for what purpose are you using steel fibres in the concrete? the primary benefit is in toughness of the surface for things like the floors of workshops used to maintain tracked vehicles.
i have used steel fibres in concrete on numerous occasions, but it was never placed by pumping. if it can be done, the supplier should be able to tell you how.
i worked on a job recently where we had 0.5% by volume of plastic fiber and had no problems pumping the mix. sure it was a bit dry and here and there we had fiberballs but they were the exception not the rule.
we did have trial mixes and placements too.
one lesson we learned was to use plasticizer.
regards,
qshake
eng-tips forums:real solutions for real problems really quick.
are you using light weight concrete? have you ahd the fiber manufacturer talk with the contractor. i had a similar situation in boston. after we got the manufacturer involved, the pumping was smooth as silk.
sounds like it could be a combination of the mix design, mixing time and possibly pump type. in any case, even if you can pump it and it balls up, it will not be effective.
mixing time (too long or too short) can be critical. pumping just complicates it, especially is it is lightweight or is pumped high.
pretty much like shotcrete - and it is pumpable (although the gradations are likely smaller in size). we found, though, that unless the machine is made for wet mix, the slumps had to be a bit higher - have you tried a plasticizer in order to increase the workability?

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