Max Fly Ash Specification Limit

[MJC6125]

Do you folks include a maximum allowable fly ash limit in your standard concrete specifications? I know Table 26.4.2.2(b) of ACI 318-19 has a limit of 25% for Exposure Class F3 concrete uses. I wasn't sure if anyone puts any other stricter limits than that? A few things I have come across is no fly-ash being allowed (due to discoloration of the concrete in architecturally exposed scenarios or based on the specs of a specific entity like a school district), a 15% limit, and a 20% limit. There's some older threads on this topic, but they were from 2011 and earlier, so I figured I'd ask to see if there's any new thoughts.

Fly Ash In Structural Concrete

what it is the reason for fly ash replacement limits?

Fly Ash in Floor Slab

 

[dauwerda]

When I worked for a power utility our spec required 20% fly ash. Other firms I worked at didn't typically address it.

It's interesting to me that some of those older posts mention better workability and finishing. Every concrete finisher I know hates fly ash because it makes the concrete "sticky". But, they hate the new 1L cement even more, basically can't finish that stuff without the use of finishing aides.