[TowerTalk] Vibrating Concrete...

K8RI on Tower talk k8ri-tower at charter.net
Sun Jun 18 23:21:54 EDT 2006

> In reference to the message and website below, I want to point something
> out about "concrete vibrating".
> It is HIGHLY recommended that you do this!  But as with anything else,
> "too much of a good thing can be BAD!"  You can actually OVER VIBRATE
> your concrete!  Let me explain...

What are your recomendations for vibrating "high fiber" concrete. We pour 
the stuff so dry it takes a vibrator to get it down the chute.

A freind down in Kentucky (just north of Carrolton) did his entire basement 
with high fiber (high strength)  some years back. I didn't pay a lot of 
attention at the time, but what I did notice was basement walls that looked 
lilke they were ready to paint.  Not a mark on them even from the forms. 
OTOH my whole house including basement and main floor would fit in one 
corner of that basement.  I'd guess the basement alone was close to 4,000 sq 
ft.  He had a hugh back yard which ended in a cliff  and steps down to the 
Ohio River. (It was a longggg way down) Man, what a place for a ham station. 
He was a ham too, but inactive and I don't know if he ever got back on 
before passing.

Roger Halstead (K8RI and ARRL 40 year Life Member)
N833R - World's oldest Debonair CD-2
> When you vibrate concrete, you are percolating the air pockets out of
> it.  These air pockets (voids) weaken the base.  As you vibrate the
> pour, you are actually causing the aggregate (rock) to move inside the
> slurry.  Gravity, being what it is, will drop the aggregate down and
> bring the "cream" to the top.  If you vibrate the pour too long, the
> aggregate (STRENGTH) will drop to the bottom of the pour!  So much for
> a strong base especially since your anchor bolts are only 27" or so
> down!
> You want to run the vibrator in and out of the pour quickly and don't
> linger in one place too long!  Once you see no more bubble coming out,
> move along!  Its best to vibrate in "lifts" as the concrete is being
> added.  Once you have vibrated a lift, don't penetrate that lift again!
> Go 2' at a time and never penetrate deeper than 2' as you go up.  Don't
> try to make air bubbles work their way up 6'!  Again, a few jabs into
> the concrete and you should be good to go!  When it comes to vibrating,
> more is NOT better!  (Is anyone else getting a little excited here or is
> it just me? HA HA!)
> While pouring basement footings and walls, I've actually seen forms
> "blow out" from too much vibrating!  All the rock went to the bottom
> and the forms (which were probably not set up correctly anyway)
> couldn't hold back the water/slurry.  What a mess!
> I have no idea if the person in the link below did it right or wrong.
> This is NOT the point of this e-mail!  The point is, DON'T OVER VIBRATE
> YOUR BASE!!!  If you don't know what you are doing, pay a few more $$
> and get someone in there who does!
> As far as the re-bar cage looks, it looks good from my house!  Seriously
> though, if the person followed the instructions as far as bar size,
> placement, and nothing moves, then all is well.
> Dino  -  K6RIX
> dino at k6rix.com
>> -------- Original Message --------
>> E.g. http://bellsouthpwp.net/k/4/k4zzr/tower1.html
>> (although I don't like the look of his rebar cage)
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