[TowerTalk] Concrete "Slump"

K7LXC at aol.com K7LXC at aol.com
Thu May 29 13:54:14 EDT 2003

In a message dated 5/29/03 9:13:02 AM Pacific Daylight Time, k3bz at arrl.net 

> Following advice received here (thanks!), I had the concrete guy here today
>  to advise on my site for a 5' x 5' x 6' deep base pour. He asked if I 
>  "3000 Lb. concrete". And he asked if I wanted a "5 inch slump".  I told him
>  I'd get back to him.  What do these terms mean? What should I want?

    My non-technical answer is that slump has to do with how 'stiff' the 
concrete is. That is, if you put it in a pile, would it stand up by itself (stiff 
with little slump) or would it run down (not stiff with lots of slump). 

    This becomes important for the top of your pour, how long it'll take for 
it to cure and when you can work it to finish it. If there's lots of slump (a 
high slump number - i.e. 9, 10, or more), it might run under your forms. A 
stiff mix (i.e. a slump of 5 or even less) will stay put more but it's harder to 
push around.  

    The slump is changed by adding water to the mix. Generally the concrete 
truck driver will start pouring and ask you if you want more water (since you 
can't take water out once it's batched). 

    For a tower base, the slump isn't too important so you can't screw it up 
no matter which way you go. 

    And don't forget to rent a concrete vibrator at your local rental yard. 
It'll move the concrete in the hole easily. 

Cheers & GL,
Steve     K7LXC

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