[TowerTalk] concrete slump

[kr7x at attbi.com]

List readers

For a quick discussion of compressive strength of concrete and slump plus other 
esoteric information go to this url:
 
http://www.portcement.org/cb/concretebasics_faqs.asp

It is my favorite url for general questions about concrete.

By the way the slump test is done using a truncated cone of specific dimensions 
and a specific tamping rod. Concrete is place and rodded in 3 equal layers (as 
I recall) in the cone. Each "lift" being rodded a specific number of times. 
When the last layer is rodded and the cone is full the top is struck(scraped) 
true to the top of the cone and the cone is carefully lifted off. The cone is 
then placed next to the pile of concrete, which has sluffed or slumped. The rod 
is placed horizontal across the top of the cone opening and the distance from 
the bottom of the rod to the top of the slumped pile of concrete is measured. 
Isn't this more than you wanted to know !!! (spent many hours doing this test 
among others at a Corps of Engineers Dam Site in Idaho after I got out of the 
University).

73

Hank Lonberg, P.E.,S.E. / KR7X
Lonberg Design Group Ltd.

p.s. Normal ready mix is usually aroung 3500 to 3750 psi, which due to the 
statistical limits of concrete testing, puts it close to the range for 4000 psi.

5" slump is ok but at the limit I would consider, use a vibrator and lessen the 
slump.