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Flyash tends to have a low early strength, but it should have about the same
ultimate strength (90 day strength) if it doesn't exceed  20% of the total
amount of cement.

I hope this helps.

Chris Towne

>Looking for information to a construction problem located in Northern 
>California regarding masonry walls... specifically grout.  I have designed 
>18' tall masonry walls.  Supported @ the top, f'm=1500 psi, special 
>inspections, 8" thick.  Temperatures have been cool but not cold.  Recent 
>grout tests are showing a low compressive break.   500 psi @ 7 days and 1400 
>psi @ 28 days.  1991 UBC code requires 2000 psi minimum.  After some 
>investigation, I found the mix design calls for 5,000 lbs. of type F 
>fly-ash.  Is this even possible???  The total numbers add up to 12 yds in a 
>9 yd truck.  Core samples have also been taken resulting in a 1750 psi 
>average strength.  Since this flyash has been noticed, different grout 
>supplier has been selected.  Using the same design without the flyash... his 
>7 day breaks have been around 1800 psi.
>        The only place I can find reference to masonry grout cores is title 
>24 of the UBC which is not in effect for this building.
>        Question.... What short-term/long-term effects will fly-ash have on 
>grout?  What other references are available regarding masonry grout cores?  
>Currently the building official is leaning towards tearing down 3,000 sq. 
>ft. of wall and maybe an additional 20,000 sq. ft. more.  Any suggestions or 
>help would be appreciated.
>        Thanks !!
>        Jeff Spence, PE
>        Spencej(--nospam--at)
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