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RE: Portlands vs. Blended Hydraulics

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Robert,
 
The classic blended hydraulic cements start with portland clinkers and have
blast furnace slag interground.  They are specified within ASTM C595.  There
is also a performance specification in ASTM C1157.  There is also an ASHTO
spec M240.  The traditional uses have been in large mat foundations and
dams.
 
There is a relatively newer generation of blended hydraulics that are using
interground flyash and/or calcined clays.  The advantages are lower cost and
better performance, but you have to specify the performance and check the
testing for confirmation to that performance.
 
You can get better sulfate resistance, lower heat of hydration, higher
strengths, better ASR, and lower permeability by specifying the proper
blended hydraulic cement.  Try getting anything other than a Type I or II
cement in today's market.  
It does requires more homework on the specifier's part.  
 
Most of the testing is for the concrete is in the hardened state.  The other
consideration is workability.  How does it place (bucket, tailgate, line
pump, or overhead pump), how does it screed (laser screeds can handle more
aggressive mixes), how does it handle in hot and cold weather, and how does
it finish (what is the finish window, what is the initial set time). This is
something that is not within the ASTM specs.  You may consider a test
placement.  Which is usually a good idea on any major concrete placement.
 
Work closely with the cement supplier and the concrete plant.  Make sure
that they are also coordinated with any admixtures.   Go outside of your
geographic area and see what is happening with cement suppliers in other
markets.  Ash Grove is doing some really interesting research in this area.
The Ash Grove Duracem http://www.duracem.com/ <http://www.duracem.com/>  is
a calcined clay cement that gets the low permeability of silica fume with a
lower cost, lower heat of hydration, and easier placement.  Check out there
tests and see how it compares with the suppliers in your market.
 
Contact the Portland Cement Association for the people who really know what
they are talking about.
 
I'll stop before I spin off into another Jimi Hendrix thread.
 
Regards,
Harold Sprague
The Neenan Company 
 

-----Original Message-----
From: Robert Rollo [mailto:rrollo(--nospam--at)TEAM-PSC.com]
Sent: Friday, June 04, 1999 10:48 AM
To: 'seaint(--nospam--at)seaint.org'
Subject: Portlands vs Blended Hydraulics



the more i look into it, the more questions i have . . . 
bottom line question is: 

What are the pros and cons of specifying one versus the other, or should i
be allowing either ? 
Costs, quality, permeability, etc 

any takers? 
harold? 

robert d. rollo, PE 
Corporate Associate 
Parkhill, Smith & Cooper, Inc. 
Lubbock, Texas 
rrollo(--nospam--at)team-psc.com 
rdrollo(--nospam--at)aol.com 
(806) 761-7539vox 
(806) 747-7146 fax