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RE: More Concrete

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Adva is a good choice because it not only acts as a great high range water reducer, but after the concrete is placed it sets faster.  That will let you get on it faster for finishing.  And will let you protect it more quickly. 
 
The rebar placement will make screeding more of a challenge.  I would urge you to look at the Copperhead Laser screed. 
http://www.somero.com/
 
Regards, Harold Sprague


 

To: seaint(--nospam--at)seaint.org
Subject: Re: More Concrete
Date: Mon, 20 Dec 2010 12:27:39 -0500
From: fsrahbar(--nospam--at)aol.com

Rick:
 
You must have done this a lot. Thank you for the advice.
 
One thing that slightly work to our advantage is the fact that the area of pour is much less than 20,000 sq. ft. we are pouring the slab, the grade beams, pile caps. The slab is an average of 13" to 14" thick. They are planning to pour this in the first week of January. The weather is going to be cool, however, we do have a concern with rain!
 
Thank you,

Farzin S. Rahbar, SE
Vice President
David C. Weiss Structural Engineer & Associates, Inc.
(818) 227-8040 Ex. 13 Fax: (818) 227-8041


-----Original Message-----
From: Rick Stone <rstone(--nospam--at)madisonconcrete.com>
To: seaint(--nospam--at)seaint.org
Sent: Mon, Dec 20, 2010 5:57 am
Subject: RE: More Concrete

Some good advice from the list. Sounds like you are trying to pour about
20,000 sf of 8 inch slab? My two cents:

1. Pumping can run at about 80 CY an hour max---so that means a truck
every 7 minutes or so---make sure the batch plant has the trucks to do
that!! Also, it may take more than that to batch each load!! Make sure
you discuss the rate of delivery needed to attain the goal. At 80 CY an
hr you'll be there a long, long time--that is 6 hrs plus just to get it
in, and then the finishing may take another 6 to 7 hours.....lots of
overtime. Costly. And if you drop to 40-50 CY/hr, you will be there a
really, really, long, long time. Quality of finish drops when the crews
are exhausted, cold, hot, hungry, tired....We plan and attain 80 CY/hr
pump rate almost all the time....to minimize fatigue.
2. Short-batching can work but planning and control are key. More
below....
3. If it is cool or cold ambient in the area that you are pouring in,
the 90 minutes may be relaxed....I know this is anathema to a lot of
designers, but it works.
4. If the slab needs to do decent numbers (Ff/Fl) the finishing gang
will not want any interruptions in service or changes in consistency
until perhaps the last 20% of the slab. Consider accelerator in the last
loads to let the finishing proceed  efficiently. If you start in the
morning when it is cold, the trucks and equipment are cold (or at least,
not hot from use) and the concrete will take longer to have an initial
set; as the day goes on the ambient climbs, equipment gets warmer
(trucks) and the set rate will pick up--try to finish with a bang,
consider accelerator.
5. Again, the steady delivery is what is needed. If there is a traffic
issue, or if it is taking longer to adjust loads upon arrival, delays
may result; make sure that you remove as many of the rocks in the road
as you can, plan the whole deal, then work the plan. 
6. That said, site trimming loads can take time, lead to excessive
discussion and thus delay. IMHO, do not short batch, relax on the 90
minutes, but make sure that the plan is sound (delivery rates, etc) and
that the plant and field crews have considered all the what-ifs.......
7. HRWR is a must for the strength you are using. A Shilstone-style
aggregate gradation may be difficult to attain in some markets (like
ours, we have crappy course runs) but it can work. Make sure that the
finishers use an evaporation retarder (E-Con, for example) and at 5000
psi, Harold mentioned the lack of bleed water. Our experience with the
Polycarboxylates at 5000 psi/7-8 in slump is that it strikes off easily,
and finishes with some but not a lot of bleeding. 
8. Test pours are considered by some specifiers to be a great idea
BUT.....in our experience, they NEVER replicate what actually happens in
the field. A test pour of 20 yards, done in an hour, in no way resembles
a large undertaking like a 500 CY pour because after 6 hours, men are
tired-their work rate and quality decrease--, weather can change,
materials will vary in consistency and temperature.... IMHO it is a
waste of time, resources, and money.

We routinely do 500 CY decks and slab on grade and have great success
with quality and finish---but we plan, plan, and plan again, check the
plan, then work that plan. Work it really hard. Good luck!!!

------------------------------------------------------------------------
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From: Harold Sprague <spraguehope(--nospam--at)hotmail.com>
To: <seaint(--nospam--at)seaint.org>
Subject: RE: More Concrete

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Farzin=2C
Tom gave you some excellent advice.  I would offer some more
considerations=
. =20
=20
1.  Have the admixture technical reps buy into the process.
=20
2.  Have a preconstruction meeting with all of the stake holders
attending =
(concrete producer=2C admixture manufacturer=2C pumper=2C finishing
contrac=
tor=2C GC=2C testing lab=2C etc.) to buy into the process.  If you use
an o=
verhead pump=2C the concrete you get at the maximum reach will not be
the s=
ame concrete as they raise the boom to its maximum height (close to the
tru=
ck).  For placing=2C I prefer 1. Tailgating if you can=3B 2.
Mini-conveyor=
=3B 3.  Bucket=3B  4.  Georgia buggy=3B 5. Horizontal line pump (slick
line=
)=3B 6. Overhead pump=3B in that order.  The method of placement
selected w=
ill have an impact on the mix.  Even the screed that you use will have
an i=
mpact.  I prefer the Copperhead laser screed.  I prefer the
polycarboxolate=
 high range water reducers=2C and I prefer a uniformly graded aggregate
(Ji=
m Shilstone lesson).  The polycarb high range mix is a bit different to
fin=
ish.  It is not hard=2C but there will not be the bleed water to which
most=
 finishers are accustomed. =20
=20
3.  Do a test pour with all of the entities and replicate the field
conditi=
ons. =20
=20
4.  Plan for the worst (break downs=2C traffic tie ups=2C etc.). =20

Regards=2C Harold Sprague


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