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Re: Free Falling Concrete

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In a message dated 4/18/99 10:50:51 AM, Tarek(--nospam--at)deltanet.com writes:
>Can anybody direct me to information regarding the free falling of concrete
>inside formed walls,is segregation an issue?
>Tarek Mokhtar, SE
>
Tarek, if you have access to American Concrete Institute publication ACI-304 
"Guide for Measuring, Mixing, Transporting, and Placing Concrete" refer to 
two pages of drawings showing correct and incorrect methods of placing 
concrete, Fig. 5.4(a-h).  

At the top of this drawing is the statement:  "CONCRETE WILL SEPARATE 
SERIOUSLY UNLESS INTRODUCED INTO FORMS PROPERLY."  

On sketch a. PLACING CONCRETE IN TOP OF NARROW FORM are 2 paragraphs:  
"Discharge concrete into light hopper feeding into light flexible drop chute. 
Separation is avoided. Forms and steel are clean until concrete covers them." 
 And: "To permit concrete from chute or buggy to strike against form and 
richochet on bars and forms faces causing separation and honeycomb at the 
bottom."  

I assure you that if good concrete is just dumped into a tall reinforced wall 
form and allowed to rattle its way to the bottom much of the cement paste 
will coat the rebar and forms and the first few inches of concrete at the 
bottom will be nothing but rocks (large aggregate) and honeycomb.  

Ralph Hueston Kratz, S.E.
Richmond CA USA