huangyhg

grout slump for piles
i was wonerding the grout slump requirements for piles and when can they be loaded. piles are design with 4000 psi grout.
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is it grout or concret your asking about? if you don't know the difference you should not be designing piles.
i was talking about grout not concrete. i was wondering if 6" to 8" is ok slump or 8" to 10" for pumping?
6" to 8" slump should be fine. 75% of the fc should be reached in 7 days. high early strength should reach 75% of fc in 3 days.
i disagree.
i just returned (today) from geo support 2004, which was held in orlando, florida. (no mickey mouse jokes, please!) one of the papers addressed the issue of the workability of the concrete mix; simply put, we use mixes that are entirely too stiff too much of the time. even a 7+ inch slump can be too stiff if the rebar spacing is tight and the coarse aggregate is too large. (for what it's worth, i've been using high slump/high workability mixes since the mid-1980's. and i haven't gotten any callbacks...)
a 4000 psi grout? it seems a bit odd, but a concrete mix with 1/4 or 3/8 inch aggregate might be thought of as a grout of sorts. i'd use a slump of 8 to 10 inches, and go higher if the rebar spacing is tight. use a water reducer to get the slump - don't just make a wet mix.
and for anyone who wants to argue about slump: do any of you know what an l-box is?
i agree with focht3 in the case of piles, it is normal to use a high slump i.e a self compacting mix. certainly i've never seen anyone trying to vibrate concrete down a pile bore. i recommend minimum 225mm slump, although at this workability a flow test can be applicable.
i have been trying to work out why grout is being proposed, are these bored piles? this isn't about grouting between the pile and the soil to increase the skin friction is it? in this case grout is applicable but workability is measured with a flow cone.
but on a slightly different subject the reason why stiff concretes are often used is that they are cheaper. for a given water/cement ratio and without using expensive admixtures a concrete with a low slump will cost less than one with a high slump. so if the compaction and finish can be achieved then 50mm slump concrete still has a place.
zambo
hmmm,
we were in agreement, zambofff">, until the last sentence. the research just doesn't support using 2 inch (50 mm) slump concrete in piers. otherwise, i agree with your post.
this is a hot topic between geotechnical and structural engineers. another hot topic is the use of tight spiral cages. the issues are inextricably intertwined -
correct i was refering to the use of 50mm slump concrete in general, i.e pile caps or slabs. for walls i would say minimum 75 - 100mm and piles (piers!!) minimum 225mm - must be self compacting.
zambo

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