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Re: Shotcrete Loading

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In a message dated 6/27/99 9:42:03 AM EST, 73527.1356(--nospam--at) writes:

<< It has been my understanding that shotcrete and Gunite are the same, 
 that Gunite is a trademarked name and shotcrete is the generic name.  Very 
 similar to specifying "framing hardware" or Simpson.
 Roger Turk, P.E.(Structural)
 Tucson, Arizona
 Laurence B. Oeth wrote:
 . > NOTE: Shotcrete and gunnite are not the same.  Shotcrete is a concrete
 . > mixture which is mixed and pumped and sprayed out the nozzle.  With
 . > gunnite, water and cementitious materials are mixed at the nozzle. 
 . > (...or did I get those two reversed?  Never can remember)  Anyway, both
 . > have advantages and disadvantes and are sensitive to the experience of
 . > the applicator.  Perhaps more for the gunnite.

They are both pneumatically placed concrete,  its just the way the components 
of the concrete (water, cementitious materials) are mixed together that are 
different.  As Mr. Oeth stated, shotcrete is premixed and then pumped through 
a hose while with gunite the components are actually mixed at the hose nozzle 
as the concrete comes out.  For concrete strength, shotcrete is more reliable 
since it is premixed.  

Shotcrete has been used extensively in many of the concrete shear wall 
seismic retrofits of older buildings in the Los Angeles area.  Getting 5000 
psi mixes for shotcrete does not appear to have been a problem either, but in 
most cases the design is often for 4000 psi.  Due to the high congestion of 
rebar in boundary elements, mockup wall panels are typically required which 
are sawcut afterwards to verify that the nozzleman can get the concrete 
placed around all the reinforcing (vertical bars, ties at 3" o.c. spacing, 
diagonal bars from coupling beam reinforcing) leaving no voids. 

I believe Gunite was developed before Shotcrete.

Note that Shotcrete is one of the papers being presented at the 1999 SEAOC 
convention at the end of September/beginning of October.

Michael Cochran